factor into workspace, improve features & deps

Cargo.lock

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+checksum = "c96395f0a926bc13b1c17622aaddda1ecb55d49c8f1bf9777e4d877800a43f8b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
 [[package]]
 name = "portable-atomic"
 version = "1.13.1"
@@ -172,6 +714,116 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand_core"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
+[[package]]
+name = "rustc_version"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
+dependencies = [
+ "semver 0.9.0",
+]
+
+[[package]]
+name = "rustc_version"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cfcb3a22ef46e85b45de6ee7e79d063319ebb6594faafcf1c225ea92ab6e9b92"
+dependencies = [
+ "semver 1.0.28",
+]
+
+[[package]]
+name = "rustversion"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
+
+[[package]]
+name = "scoped-tls"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1cf6437eb19a8f4a6cc0f7dca544973b0b78843adbfeb3683d1a94a0024a294"
+
+[[package]]
+name = "scopeguard"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
+
+[[package]]
+name = "semver"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
+dependencies = [
+ "semver-parser",
+]
+
+[[package]]
+name = "semver"
+version = "1.0.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a7852d02fc848982e0c167ef163aaff9cd91dc640ba85e263cb1ce46fae51cd"
+
+[[package]]
+name = "semver-parser"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+
+[[package]]
+name = "sharded-slab"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40ca3c46823713e0d4209592e8d6e826aa57e928f09752619fc696c499637f6"
+dependencies = [
+ "lazy_static",
+]
+
+[[package]]
+name = "shlex"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
+
+[[package]]
+name = "smallvec"
+version = "1.15.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67b1b7a3b5fe4f1376887184045fcf45c69e92af734b7aaddc05fb777b6fbd03"
+
+[[package]]
+name = "spin"
+version = "0.9.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
+dependencies = [
+ "lock_api",
+]
+
 [[package]]
 name = "stable_deref_trait"
 version = "1.2.1"
@@ -184,6 +836,15 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 
+[[package]]
+name = "static_cell"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0530892bb4fa575ee0da4b86f86c667132a94b74bb72160f58ee5a4afec74c23"
+dependencies = [
+ "portable-atomic",
+]
+
 [[package]]
 name = "syn"
 version = "2.0.117"
@@ -215,6 +876,82 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thread_local"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f60246a4944f24f6e018aa17cdeffb7818b76356965d03b07d6a9886e8962185"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "tracing"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63e71662fa4b2a2c3a26f570f037eb95bb1f85397f3cd8076caed2f026a6d100"
+dependencies = [
+ "pin-project-lite",
+ "tracing-attributes",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-attributes"
+version = "0.1.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7490cfa5ec963746568740651ac6781f701c9c5ea257c58e057f3ba8cf69e8da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tracing-core"
+version = "0.1.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
+dependencies = [
+ "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.3.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb7f578e5945fb242538965c2d0b04418d38ec25c79d160cd279bf0731c8d319"
+dependencies = [
+ "matchers",
+ "nu-ansi-term",
+ "once_cell",
+ "regex-automata",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
+ "tracing",
+ "tracing-core",
+ "tracing-log",
+]
+
+[[package]]
+name = "typenum"
+version = "1.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "40ce102ab67701b8526c123c1bab5cbe42d7040ccfd0f64af1a385808d2f43de"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"
@@ -228,7 +965,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "98816b1accafbb09085168b90f27e93d790b4bfa19d883466b5e53315b5f06a6"
 dependencies = [
  "defmt 0.3.100",
- "heapless",
+ "heapless 0.8.0",
  "portable-atomic",
 ]
 
@@ -237,9 +974,66 @@ name = "usbd-uac2"
 version = "0.1.0"
 dependencies = [
  "byteorder-embedded-io",
- "defmt 1.0.1",
+ "defmt 1.1.0",
  "embedded-io",
  "modular-bitfield",
  "num-traits",
  "usb-device",
 ]
+
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
+[[package]]
+name = "vcell"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77439c1b53d2303b20d9459b1ade71a83c716e3f9c34f3228c00e6f185d6c002"
+
+[[package]]
+name = "version_check"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
+
+[[package]]
+name = "void"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a02e4885ed3bc0f2de90ea6dd45ebcbb66dacffe03547fadbb0eeae2770887d"
+
+[[package]]
+name = "volatile-register"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "de437e2a6208b014ab52972a27e59b33fa2920d3e00fe05026167a1c509d19cc"
+dependencies = [
+ "vcell",
+]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-result"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7781fa89eaf60850ac3d2da7af8e5242a5ea78d1a11c49bf2910bb5a73853eb5"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]

Cargo.toml

@@ -1,10 +1,21 @@
+[workspace]
+members = [
+    "examples/lpc55s28-evk",
+    "examples/lpc55s28-evk-dma"
+]
+resolver = "2"
+
+[workspace.dependencies]
+usb-device = { version = "0.3", features = ["control-buffer-256"] }
+usbd-uac2 = { path = "." }
+
 [package]
 name = "usbd-uac2"
 description = "USB Audio Class 2.0 for usb-device"
 authors = ["Keenan Tims <ktims@gotroot.ca>"]
 version = "0.1.0"
 edition = "2024"
-keywords = ["no-std", "usb-device"]
+keywords = ["no-std", "usb-device", "audio"]
 
 [features]
 defmt = ["dep:defmt", "usb-device/defmt"]
@@ -15,4 +26,4 @@ defmt = { version = "1.0.1", optional = true }
 embedded-io = "0.7.1"
 modular-bitfield = "0.13.1"
 num-traits = { version = "0.2.19", default-features = false }
-usb-device = { version = "0.3", features = ["control-buffer-256"] }
+usb-device.workspace = true

examples/README.md

@@ -0,0 +1,48 @@
+# usbd-uac2 Examples
+
+This repository contains example implementations of a USB Audio Class 2 (UAC2) device.
+
+Two example backends are provided, both based on the LPCXpresso55S28 demo board, using the onboard WM8904 DAC:
+
+- **Interrupt-driven example** (`lpc55s28-evk`)
+- **DMA-based example** (`lpc55s28-evk-dma`)
+
+
+## Examples Overview
+
+### Interrupt-driven (`lpc55s28-evk`)
+
+Running at 32bit/48khz. It can't keep up at 96khz. Works on USBFS and USBHS.
+
+This is a minimal implementation intended to demonstrate the fundamental
+structure of the class driver. It fills a `bbqueue` as data comes in from USB,
+and drains it into the I2S FIFO in the I2S interrupt. This requires a lot of
+time-critical CPU work managing buffers. Particularly, the USB peripheral driver
+uses a lot of interrupt-free critical sections which can cause late interrupts
+and underruns.
+
+This is intended primarily as a learning/reference implementation
+
+### DMA-based (`lpc55s28-evk-dma`)
+
+Running at 32bit/96khz. Works on USBFS and USBHS.
+
+A more realistic and robust implementation using DMA. It fills a static ring
+buffer as data comes in from USB, while the DMA chases it around the ring,
+draining into the TX FIFO. This is efficient and decouples interrupt latency
+from data delivery. It uses the DMA interrupt to track consumed slots, but as
+long as the USB doesn't catch up to the read slot before this happens, there is
+a lot of slack for other things to be happening.
+
+This is a more useful demonstration, but is still lacking correct handling of
+edge cases, error conditions and so on you would want in a fully fleshed out
+implementation. Particularly, it behaves poorly in underrun, since the DMA will
+keep emitting from the ring regardless of whether the data is valid, which
+sounds terrible.
+
+## Running the Examples
+
+You can flash and run either example using `cargo embed`:
+
+```sh
+cargo embed --release --example lpc55s28-evk --features usbfs

examples/lpc55s28-evk-dma/Cargo.lock

@@ -313,6 +313,7 @@ dependencies = [
 [[package]]
 name = "lpc55-hal"
 version = "0.5.0"
+source = "git+https://github.com/ktims/lpc55-hal?branch=main#8dfefd62aff4abd2de535f23107812dda68437be"
 dependencies = [
  "block-buffer",
  "cipher",
@@ -353,7 +354,6 @@ dependencies = [
  "log-to-defmt",
  "lpc55-hal",
  "nb 1.1.0",
- "panic-halt",
  "panic-probe",
  "static_cell",
  "usb-device",
@@ -458,12 +458,6 @@ dependencies = [
  "autocfg",
 ]
 
-[[package]]
-name = "panic-halt"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a513e167849a384b7f9b746e517604398518590a9142f4846a32e3c2a4de7b11"
-
 [[package]]
 name = "panic-probe"
 version = "1.0.0"

examples/lpc55s28-evk-dma/Cargo.toml

@@ -2,6 +2,7 @@
 name = "lpc55s28-evk-dma"
 version = "0.1.0"
 edition = "2024"
+publish = false
 
 [features]
 default = ["usbhs"]
@@ -16,13 +17,13 @@ defmt-rtt = "1.1.0"
 embedded-hal = "1.0.0"
 embedded-io = "0.7.1"
 log-to-defmt = "0.1.0"
-lpc55-hal = { version = "0.5.0", path = "../lpc55-hal" }
 nb = "1.1.0"
-panic-halt = "1.0.0"
 panic-probe = { version = "1.0.0", features = ["print-defmt"] }
 static_cell = "2.1.1"
-usb-device = "0.3"
+# Includes update to usb-device 0.3, fix for isochronous and smaller critical sections
-usbd-uac2 = { version = "0.1.0", path = "../..", features = ["defmt"]}
+lpc55-hal = { git = "https://github.com/ktims/lpc55-hal", branch = "main" }
+usb-device.workspace = true
+usbd-uac2 = { workspace = true, features = ["defmt"] }
 
 [profile.release]
 opt-level = "z"

examples/lpc55s28-evk-dma/Embed.toml

@@ -0,0 +1,9 @@
+[default.general]
+chip = "LPC55S28JBD100"
+[default.rtt]
+enabled = true
+[default.gdb]
+enabled = true
+
+[debug.rtt]
+enabled = false

examples/lpc55s28-evk-dma/build.rs

@@ -0,0 +1,5 @@
+// Find the actual path of memory.x and add it to link search, required for building in workspace
+fn main() {
+    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+    println!("cargo:rustc-link-search={}", manifest_dir);
+}

examples/lpc55s28-evk-dma/src/dma.rs

@@ -233,13 +233,37 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize> DmaRing<N, MAX_SLOT_BYTES> {
     pub fn produced(&self) -> usize {
         self.produced.load(Ordering::Acquire)
     }
-
+    pub fn produced_bytes(&self) -> usize {
+        self.produced_bytes.load(Ordering::Acquire)
+    }
     pub fn consumed(&self) -> usize {
         self.consumed.load(Ordering::Acquire)
     }
     pub fn consumed_bytes(&self) -> usize {
-        self.consumed.load(Ordering::Acquire) * self.slot_bytes
+        loop {
-            + (self.dma.channel19.xfercfg.read().bits() as usize >> 16 & 0x3ff)
+            let consumed_start = self.consumed.load(Ordering::Acquire);
+
+            let reg_1 = self.dma.channel19.xfercfg.read().bits() as usize >> 16 & 0x3ff;
+            let reg_2 = self.dma.channel19.xfercfg.read().bits() as usize >> 16 & 0x3ff;
+
+            let consumed_end = self.consumed.load(Ordering::Acquire);
+
+            if consumed_start == consumed_end && reg_1 == reg_2 {
+                // 1. Map the hardware remaining countdown into a clean byte count
+                let remaining_bytes = if reg_1 == 0x3ff {
+                    0 // 0x3FF means all transfers completed, 0 bytes remaining
+                } else {
+                    // Formula from NXP manual: (XFERCOUNT + 1) * Data Width
+                    (reg_1 + 1) * self.word_bytes
+                };
+
+                // 2. Total bytes consumed in this specific active slot
+                let active_slot_consumed = self.slot_bytes - remaining_bytes;
+
+                // 3. Combine with your software index history accumulator
+                return consumed_start * self.slot_bytes + active_slot_consumed;
+            }
+        }
     }
 
     pub fn fill_slots(&self) -> usize {
@@ -319,7 +343,7 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize> DmaRing<N, MAX_SLOT_BYTES> {
         let slots = unsafe { &mut *self.slots.get() };
         let desc = unsafe { &mut *self.desc.get() };
         let chan_desc = unsafe { &mut *self.channel_desc.get() };
-        defmt::info!("slots base: &{:x}", self.slots.get());
+        defmt::debug!("slots base: &{:x}", self.slots.get());
 
         // Pre-fill with silence so underrun replays silence.
         for i in 0..N {

examples/lpc55s28-evk-dma/src/hw.rs

@@ -1,22 +1,19 @@
 //! Contains hardware setup unrelated to Usb Audio Class implementation
 
-use crate::hal;
-use core::cell::{OnceCell, UnsafeCell};
-use core::mem::MaybeUninit;
-use core::ptr::null_mut;
-
 use crate::Syscon;
+use crate::hal;
 use crate::{MCLK_FREQ, SAMPLE_RATE, pac};
-use defmt::debug;
+
+use core::cell::UnsafeCell;
+use core::mem::MaybeUninit;
+use defmt::{debug, info};
 use hal::{
-    Iocon, Pin,
+    Enabled, Iocon, Pin,
     drivers::pins,
-    prelude::*,
     traits::wg::digital::v2::{OutputPin, ToggleableOutputPin},
     typestates::pin::{gpio::direction::Output, state::Gpio},
 };
-use lpc55_hal::Enabled;
+
-use static_cell::StaticCell;
 pub(crate) struct PllConstants {
     pub m: u16,   // 1-65535
     pub n: u8,    // 1-255
@@ -138,67 +135,12 @@ pub(crate) fn init_audio_pll() {
 
     pmc.pdruncfg0
         .modify(|_, w| w.pden_pll0().poweredon().pden_pll0_sscg().poweredon());
-    debug!("pll0 wait for lock");
+    info!("pll0 wait for lock");
     let mut i = 0usize;
     while syscon.pll0stat.read().lock().bit_is_clear() {
         i += 1;
     }
-    debug!("pll0 locked after {} tries", i);
+    info!("pll0 locked after {} loops", i);
-}
-
-const SYS_PLL: PllConstants = PllConstants::new(4, 75, 1); // 150MHz
-
-pub(crate) fn init_sys_pll1() {
-    let syscon = unsafe { &*pac::SYSCON::ptr() };
-    let pmc = unsafe { &*pac::PMC::ptr() };
-    let anactrl = unsafe { &*pac::ANACTRL::ptr() };
-
-    debug!("start clk_in");
-    pmc.pdruncfg0
-        .modify(|_, w| w.pden_xtal32m().poweredon().pden_ldoxo32m().poweredon());
-    syscon.clock_ctrl.modify(|_, w| w.clkin_ena().enable());
-    anactrl
-        .xo32m_ctrl
-        .modify(|_, w| w.enable_system_clk_out().enable());
-
-    debug!("init pll1: {}", SYS_PLL);
-    pmc.pdruncfg0.modify(|_, w| w.pden_pll1().poweredoff());
-    syscon.pll1clksel.write(|w| w.sel().enum_0x1()); // clk_in
-    syscon.pll1ctrl.write(|w| unsafe {
-        w.clken()
-            .enable()
-            .seli()
-            .bits(SYS_PLL.seli)
-            .selp()
-            .bits(SYS_PLL.selp)
-    });
-
-    syscon
-        .pll1ndec
-        .write(|w| unsafe { w.ndiv().bits(SYS_PLL.n) });
-    syscon.pll1ndec.write(|w| unsafe {
-        w.ndiv().bits(SYS_PLL.n).nreq().set_bit() // latch
-    });
-    syscon
-        .pll1mdec
-        .write(|w| unsafe { w.mdiv().bits(SYS_PLL.m) });
-    syscon
-        .pll1pdec
-        .write(|w| unsafe { w.pdiv().bits(SYS_PLL.p) });
-    syscon.pll1pdec.write(|w| unsafe {
-        w.pdiv().bits(SYS_PLL.p).preq().set_bit() // latch
-    });
-
-    pmc.pdruncfg0.modify(|_, w| w.pden_pll1().poweredon());
-    debug!("pll1 wait for lock");
-    let mut i = 0usize;
-    while syscon.pll1stat.read().lock().bit_is_clear() {
-        i += 1;
-    }
-    debug!("pll1 locked after {} tries", i);
-    // switch system clock to pll1
-    syscon.fmccr.modify(|_, w| w.flashtim().flashtim11());
-    syscon.mainclkselb.modify(|_, w| w.sel().enum_0x2()); // pll1
 }
 
 pub struct I2sTx {
@@ -207,7 +149,6 @@ pub struct I2sTx {
 
 pub fn init_i2s(mut fc7: pac::FLEXCOMM7, i2s7: pac::I2S7, syscon: &mut Syscon) -> I2sTx {
     defmt::debug!("init i2s");
-    // Enable BOTH
     syscon.reset(&mut fc7);
     syscon.enable_clock(&mut fc7);
 

examples/lpc55s28-evk-dma/src/main.rs

@@ -1,10 +1,15 @@
-//! Interrupt driven example for the LPCXpresso55S28 demo board
+//! DMA based audio output example for the LPCXpresso55S28 demo board
 //!
-//! Uses the onboard WM8904 DAC at 48KHz. Clock is generated by PLL0. Simple PI feedback
+//! Uses the onboard WM8904 DAC at 96KHz. Clock is generated by PLL0. Simple proportional feedback is implemented.
-//! is implemented.
 //!
-//! Packets from USB are placed a `heapless::spsc::Queue`. They are consumed
+//! USB walks around a static ring of slots, filling them as data comes in from
-//! by the I2S FIFO in the FLEXCOMM7 interrupt.
+//! the host. DMA chases it, filling the I2S FIFO as it drains to the DAC.
+//! Feedback ensures that the host doesn't overrun or underrun the ring.
+//!
+//! This implementation is more suitable for real use than the interrupt-based
+//! example, but it is still missing many niceties and behaves worse in
+//! anomalous situations since the DMA just keeps trucking over the ring
+//! regardless of the data validity.
 #![no_main]
 #![no_std]
 
@@ -34,13 +39,11 @@ use static_cell::StaticCell;
 use usb_device::{
     bus::{self},
     device::{StringDescriptors, UsbDeviceBuilder, UsbVidPid},
-    endpoint::IsochronousSynchronizationType,
 };
-use usbd_uac2::UsbIsochronousFeedback;
+use usbd_uac2::TerminalConfig;
 use usbd_uac2::{
-    self, AudioClassConfig, RangeEntry, TerminalConfig, UsbAudioClass, UsbAudioClockImpl, UsbSpeed,
+    self, AudioHandler, ClockSource, RangeEntry, UsbAudioClassConfig, UsbIsochronousFeedback,
-    constants::{FunctionCode, TerminalType},
+    UsbSpeed, constants::FunctionCode, descriptors::ClockType,
-    descriptors::{ChannelConfig, ClockType, FormatType1, LockDelay},
 };
 
 use crate::dma::DmaRing;
@@ -52,41 +55,27 @@ mod wm8904;
 
 const CODEC_I2C_ADDR: u8 = 0b0011010;
 const MCLK_FREQ: u32 = 12288000;
+
 const SAMPLE_RATE: u32 = 96000;
+const USB_FRAME_RATE: u32 = if cfg!(feature = "usbhs") { 8000 } else { 1000 };
+
 //latency ≈ (current_fill × FRAMES_PER_SLOT)
 //              + FRAMES_PER_SLOT/2 - average DMA transfer position
 //              + 8 - FIFO depth @ 32-bit samples
+// with example values, ~2.3ms
 const BYTES_PER_SAMPLE: usize = 4; // 32 bit samples
 const BYTES_PER_FRAME: usize = BYTES_PER_SAMPLE * 2; // 2 channels
 const FRAMES_PER_SLOT: usize = SAMPLE_RATE as usize / 2000; // run the DMA at 2khz
-const SLOT_SIZE_BYTES: usize = FRAMES_PER_SLOT * BYTES_PER_FRAME; // run the DMA at 2khz
+const BYTES_PER_SLOT: usize = FRAMES_PER_SLOT * BYTES_PER_FRAME;
-const N_SLOTS: usize = 32;
+const N_SLOTS: usize = 8;
-const FILL_TARGET: i32 = (FRAMES_PER_SLOT * N_SLOTS) as i32 / 2;
+const FILL_TARGET_BYTES: i32 = (BYTES_PER_SLOT * N_SLOTS) as i32 / 2;
 
-struct Clock {}
+const LOG_PERIOD: u32 = 1000;
-impl Clock {
-    const RATES: [RangeEntry<u32>; 1] = [RangeEntry::new_fixed(SAMPLE_RATE)];
-}
-impl UsbAudioClockImpl for Clock {
-    const CLOCK_TYPE: usbd_uac2::descriptors::ClockType = ClockType::InternalFixed;
-    const SOF_SYNC: bool = false;
-    fn get_sample_rate(&self) -> u32 {
-        Clock::RATES[0].min
-    }
-    fn get_rates(
-        &self,
-    ) -> core::result::Result<&[usbd_uac2::RangeEntry<u32>], usbd_uac2::UsbAudioClassError> {
-        Ok(&Clock::RATES)
-    }
-    fn get_clock_validity(&self) -> core::result::Result<bool, usbd_uac2::UsbAudioClassError> {
-        Ok(true)
-    }
-}
 
-static DMA_RING: StaticCell<DmaRing<N_SLOTS, SLOT_SIZE_BYTES>> = StaticCell::new();
+static DMA_RING: StaticCell<DmaRing<N_SLOTS, BYTES_PER_SLOT>> = StaticCell::new();
-static mut DMA_RING_REF: Option<&'static DmaRing<N_SLOTS, SLOT_SIZE_BYTES>> = None;
+static mut DMA_RING_REF: Option<&'static DmaRing<N_SLOTS, BYTES_PER_SLOT>> = None;
 #[inline]
-fn dma_ring() -> &'static DmaRing<N_SLOTS, SLOT_SIZE_BYTES> {
+fn dma_ring() -> &'static DmaRing<N_SLOTS, BYTES_PER_SLOT> {
     unsafe { DMA_RING_REF.unwrap() }
 }
 
@@ -125,13 +114,15 @@ struct Audio<'a, const N: usize, const MAX_SLOT_BYTES: usize> {
     running: AtomicBool,
     i2s: I2sTx,
     dma: &'a DmaRing<N, MAX_SLOT_BYTES>,
+    log_counter: u32,
 }
 impl<const N: usize, const MAX_SLOT_BYTES: usize> Audio<'_, N, MAX_SLOT_BYTES> {
-    fn start(&self) {
+    const RATES: [RangeEntry<u32>; 1] = [RangeEntry::new_fixed(SAMPLE_RATE)];
+    fn start(&mut self) {
         red_led().off(); // clear any dma error
         self.running.store(false, Ordering::Relaxed);
 
-        defmt::info!("playback starting (DMA)");
+        defmt::info!("playback armed (DMA)");
 
         let i2s = &self.i2s.i2s;
         i2s.fifotrig
@@ -150,15 +141,15 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize> Audio<'_, N, MAX_SLOT_BYTES> {
         // If we don't disable interrupts while stopped, we will underflow constantly and continuously refill the fifo with 0s
         // We could actually stop the I2S here, but sometimes that makes the DAC misbehave. The peripheral is configured to send
         // 0s when the FIFO is empty, so this is fine.
+        pac::NVIC::mask(pac::Interrupt::DMA0);
         self.running.store(false, Ordering::Relaxed);
         dma_ring().stop();
         defmt::info!("playback stopped");
-        pac::NVIC::mask(pac::Interrupt::DMA0);
         green_led().off();
         blue_led().off();
     }
 }
-impl<const N: usize, const MAX_SLOT_BYTES: usize, B: bus::UsbBus> UsbAudioClass<'_, B>
+impl<const N: usize, const MAX_SLOT_BYTES: usize, B: bus::UsbBus> AudioHandler<'_, B>
     for Audio<'_, N, MAX_SLOT_BYTES>
 {
     fn alternate_setting_changed(&mut self, _terminal: usb_device::UsbDirection, alt_setting: u8) {
@@ -174,7 +165,8 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize, B: bus::UsbBus> UsbAudioClass<
         ep: &usb_device::endpoint::Endpoint<'_, B, usb_device::endpoint::Out>,
     ) {
         // Buffer must fit 125us of audio data (based on how `usbd_uac2` sets up the descriptors).
-        let mut buf = [0; SAMPLE_RATE.div_ceil(8000) as usize * BYTES_PER_FRAME];
+        // Buffer must have room for one additional frame in case the host clock runs slower than the device.
+        let mut buf = [0; (SAMPLE_RATE.div_ceil(USB_FRAME_RATE) + 1) as usize * BYTES_PER_FRAME];
 
         let len = match ep.read(&mut buf) {
             Ok(len) => len,
@@ -199,8 +191,8 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize, B: bus::UsbBus> UsbAudioClass<
         }
         // If we're not running yet, wait until we reach 50% full then enable DMA requests
         if !self.running.load(Ordering::Relaxed) && self.dma.fill_slots() >= (N_SLOTS / 2) {
-            defmt::debug!(
+            defmt::info!(
-                "buffer has {} slots, start dma transfers",
+                "buffer warmed ({} slots) starting playback",
                 self.dma.fill_slots()
             );
             self.dma.run();
@@ -208,52 +200,76 @@ impl<const N: usize, const MAX_SLOT_BYTES: usize, B: bus::UsbBus> UsbAudioClass<
         }
     }
 
-    /// Provide rate feedback to the host, so that it doesn't over- or underflow
+    /// Provide rate feedback to the host. P-only is stable and works fine, with
-    /// the buffer. Proportional-only control is stable with normal hosts,
+    /// most hosts. The host can either filter it internally or treat it
-    /// adding an I term with proper tuning (quite weak) would stabilize the
+    /// instantaneously and send more data specifically when the error gets
-    /// rate reported to the host but is not necessary for basic playback.
+    /// large; we will absorb reasonable clock drifts with our ring buffer.
     fn feedback(&mut self, nominal_rate: UsbIsochronousFeedback) -> Option<UsbIsochronousFeedback> {
-        const MAX_CORRECTION: i32 = 1 << 10; // ~1.6%
+        // Don't want to signal an absurd rate when not consuming; let the
+        // buffer fill before starting feedback.
+        if !self.running.load(Ordering::Acquire) {
+            return Some(nominal_rate);
+        }
 
-        let produced_bytes = self.dma.produced_bytes.load(Ordering::Acquire);
+        let produced_bytes = self.dma.produced_bytes();
         let consumed_bytes = self.dma.consumed_bytes();
 
-        let valid = produced_bytes >= consumed_bytes; // else we are in underrun condition
+        if produced_bytes < consumed_bytes || produced_bytes == 0 {
+            defmt::error!("[fb] dma underrun detected!");
+            red_led().on();
+            return Some(nominal_rate);
+        }
 
-        let fill_frames = if valid {
+        let current_bytes = (produced_bytes - consumed_bytes) as i32;
-            (produced_bytes - consumed_bytes) as i32 / BYTES_PER_FRAME as i32
+        // normalize error wrt. frame size etc.
-        } else {
+        let error_permille = ((current_bytes - FILL_TARGET_BYTES) * 1000) / FILL_TARGET_BYTES;
-            // we will emit a canonical error in the DMA ISR
-            defmt::debug!("[fb] dma underrun detected");
-            0
-        };
-
-        let mut error = fill_frames - FILL_TARGET;
-        error = error.clamp(-32, 32); // avoid huge spikes
-
-        let p = error * 256;
-        let i = 0; // placeholder
-
-        let correction = -(p + i);
 
         let nominal_v = nominal_rate.to_u32_12_13() as i32;
 
-        let mut v = nominal_v + correction;
+        // 0.2% which is a huge clock error
+        let max_allowed_deviation = nominal_v / 500;
 
-        v = v.clamp(nominal_v - MAX_CORRECTION, nominal_v + MAX_CORRECTION);
+        let p_term = -(error_permille * nominal_v) / 256000; // this works reasonably well to keep the buffer 
+        let i_term = 0; // placeholder
 
-        defmt::debug!(
+        let mut v = nominal_v + p_term + i_term;
-            "valid:{} fill:{} err:{} fb:{=u32:x}",
+        v = v.clamp(
-            valid,
+            nominal_v - max_allowed_deviation,
-            fill_frames,
+            nominal_v + max_allowed_deviation,
-            error,
-            v as u32
         );
+        self.log_counter += 1;
+        if self.log_counter.is_multiple_of(LOG_PERIOD) {
+            defmt::info!(
+                "fill:{}% err_pm:{} p:{} i:{} fb_delta:{} fb:{=u32:x}",
+                (current_bytes * 100) / (N_SLOTS * BYTES_PER_SLOT) as i32,
+                error_permille,
+                p_term,
+                i_term,
+                v - nominal_v,
+                v as u32
+            );
+        }
 
         Some(UsbIsochronousFeedback::new(v as u32))
     }
 }
 
+impl<const N: usize, const MAX_SLOT_BYTES: usize> ClockSource for Audio<'_, N, MAX_SLOT_BYTES> {
+    const CLOCK_TYPE: usbd_uac2::descriptors::ClockType = ClockType::InternalFixed;
+    const SOF_SYNC: bool = false;
+    fn sample_rate(&self) -> u32 {
+        Self::RATES[0].min
+    }
+    fn sample_rates(
+        &self,
+    ) -> core::result::Result<&[usbd_uac2::RangeEntry<u32>], usbd_uac2::UsbAudioClassError> {
+        Ok(&Self::RATES)
+    }
+    fn clock_validity(&self) -> core::result::Result<bool, usbd_uac2::UsbAudioClassError> {
+        Ok(true)
+    }
+}
+
 #[entry]
 fn main() -> ! {
     let hal = hal::new();
@@ -277,7 +293,7 @@ fn main() -> ! {
         pins::Pio1_20::take().unwrap().into_i2c4_scl_pin(&mut iocon),
         pins::Pio1_21::take().unwrap().into_i2c4_sda_pin(&mut iocon),
     );
-    // We can initialize and iocon these, but there is no peripheral, so they do not get used
+    // We can initialize and iocon these, but there is no peripheral driver, so they do not get used
     let _codec_i2s_pins = (
         pins::Pio0_21::take().unwrap().into_spi7_sck_pin(&mut iocon),
         pins::Pio0_20::take().unwrap().into_i2s7_sda_pin(&mut iocon),
@@ -286,18 +302,16 @@ fn main() -> ! {
     );
 
     debug!("clocks");
-    // Run the system clock at 96MHz. The lpc55-hal will run it from the FRO. But we won't actually use these clocks, we just need the guards...
     let clocks = hal::ClockRequirements::default()
         .system_frequency(96.MHz())
         .configure(&mut anactrl, &mut pmc, &mut syscon)
         .unwrap();
-    let mut _delay_timer = Timer::new(
+    let mut usb_delay_timer = Timer::new(
         hal.ctimer
             .0
             .enabled(&mut syscon, clocks.support_1mhz_fro_token().unwrap()),
     );
-    // Start PLL1 at 150MHz as main system clock
+
-    hw::init_sys_pll1();
     // Start PLL0 at 24.576MHz as the audio clock. The FRO cannot evenly divide
     // any common audio frequencies and is not particularly stable anyway.
     hw::init_audio_pll();
@@ -326,7 +340,7 @@ fn main() -> ! {
             &mut anactrl,
             &mut pmc,
             &mut syscon,
-            &mut _delay_timer,
+            &mut usb_delay_timer,
             clocks.support_usbhs_token().unwrap(),
         ),
     );
@@ -348,34 +362,21 @@ fn main() -> ! {
 
     defmt::debug!("dma init");
     let i2s_dma_addr = &i2s_peripheral.i2s.fifowr as *const _ as *mut u32;
-    let dma = DmaRing::<32, SLOT_SIZE_BYTES>::new(hal.dma.release(), &mut syscon, i2s_dma_addr, 4)
+    let dma =
-        .unwrap();
+        DmaRing::<N_SLOTS, BYTES_PER_SLOT>::new(hal.dma.release(), &mut syscon, i2s_dma_addr, 4)
+            .unwrap();
     let dma_ref = DMA_RING.init(dma);
     unsafe { DMA_RING_REF = Some(dma_ref) };
 
-    let mut clock = Clock {};
     let mut audio = Audio {
         i2s: i2s_peripheral,
         dma: dma_ring(),
         running: AtomicBool::new(false),
+        log_counter: 0,
     };
     defmt::debug!("usb init");
-    let config = AudioClassConfig::new(usb_speed, FunctionCode::Other, &mut clock, &mut audio)
+    let config = UsbAudioClassConfig::new(usb_speed, FunctionCode::IoBox, &mut audio)
-        .with_output_config(TerminalConfig::new(
+        .with_output_config(TerminalConfig::builder().base_id(2).build());
-            4,
-            1,
-            2,
-            FormatType1 {
-                bit_resolution: 32,
-                bytes_per_sample: 4,
-            },
-            TerminalType::ExtLineConnector,
-            ChannelConfig::default_chans(2),
-            IsochronousSynchronizationType::Asynchronous,
-            LockDelay::Milliseconds(10),
-            None,
-        ));
-
     let mut uac2 = config.build(&usb_bus).unwrap();
 
     let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x1209, 0xcc1d))

examples/lpc55s28-evk/.cargo/config.toml

@@ -16,4 +16,4 @@ rustflags = [
 target = "thumbv8m.main-none-eabihf"
 
 [env]
-DEFMT_LOG = "info"
+DEFMT_LOG = "off"

examples/lpc55s28-evk/Cargo.lock

@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "atomic-polyfill"
 version = "1.0.3"
@@ -26,6 +35,17 @@ dependencies = [
  "rustc_version 0.2.3",
 ]
 
+[[package]]
+name = "bbqueue"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68917624e17aad88607cb5a5936f6da9b607c48c711e4e9ed101e7189aed28c2"
+dependencies = [
+ "const-init",
+ "critical-section",
+ "maitake-sync",
+]
+
 [[package]]
 name = "bitfield"
 version = "0.13.2"
@@ -63,6 +83,22 @@ dependencies = [
  "embedded-io",
 ]
 
+[[package]]
+name = "cc"
+version = "1.2.61"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d16d90359e986641506914ba71350897565610e87ce0ad9e6f28569db3dd5c6d"
+dependencies = [
+ "find-msvc-tools",
+ "shlex",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
 [[package]]
 name = "cipher"
 version = "0.4.4"
@@ -73,6 +109,22 @@ dependencies = [
  "inout",
 ]
 
+[[package]]
+name = "const-init"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4bd422bfb4f24a97243f60b6a4443e63d810c925d8da4bb2d8fde26a7c1d57ec"
+
+[[package]]
+name = "cordyceps"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "688d7fbb8092b8de775ef2536f36c8c31f2bc4006ece2e8d8ad2d17d00ce0a2a"
+dependencies = [
+ "loom",
+ "tracing",
+]
+
 [[package]]
 name = "cortex-m"
 version = "0.7.7"
@@ -214,6 +266,27 @@ dependencies = [
  "num",
 ]
 
+[[package]]
+name = "find-msvc-tools"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5baebc0774151f905a1a2cc41989300b1e6fbb29aff0ceffa1064fdd3088d582"
+
+[[package]]
+name = "generator"
+version = "0.8.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "52f04ae4152da20c76fe800fa48659201d5cf627c5149ca0b707b69d7eef6cf9"
+dependencies = [
+ "cc",
+ "cfg-if",
+ "libc",
+ "log",
+ "rustversion",
+ "windows-link",
+ "windows-result",
+]
+
 [[package]]
 name = "generic-array"
 version = "0.14.7"
@@ -275,16 +348,6 @@ dependencies = [
  "stable_deref_trait",
 ]
 
-[[package]]
-name = "heapless"
-version = "0.9.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "25ba4bd83f9415b58b4ed8dc5714c76e626a105be4646c02630ad730ad3b5aa4"
-dependencies = [
- "hash32 0.3.1",
- "stable_deref_trait",
-]
-
 [[package]]
 name = "inout"
 version = "0.1.4"
@@ -294,6 +357,18 @@ dependencies = [
  "generic-array 0.14.7",
 ]
 
+[[package]]
+name = "lazy_static"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
+
+[[package]]
+name = "libc"
+version = "0.2.186"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68ab91017fe16c622486840e4c83c9a37afeff978bd239b5293d61ece587de66"
+
 [[package]]
 name = "lock_api"
 version = "0.4.14"
@@ -320,9 +395,23 @@ dependencies = [
  "log",
 ]
 
+[[package]]
+name = "loom"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "419e0dc8046cb947daa77eb95ae174acfbddb7673b4151f56d1eed8e93fbfaca"
+dependencies = [
+ "cfg-if",
+ "generator",
+ "scoped-tls",
+ "tracing",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "lpc55-hal"
 version = "0.5.0"
+source = "git+https://github.com/ktims/lpc55-hal?branch=main#8dfefd62aff4abd2de535f23107812dda68437be"
 dependencies = [
  "block-buffer",
  "cipher",
@@ -354,23 +443,51 @@ dependencies = [
 name = "lpc55s28-evk"
 version = "0.1.0"
 dependencies = [
+ "bbqueue",
  "cortex-m",
  "cortex-m-rt",
  "defmt 1.0.1",
  "defmt-rtt",
  "embedded-hal 1.0.0",
  "embedded-io",
- "heapless 0.9.3",
  "log-to-defmt",
  "lpc55-hal",
- "nb 1.1.0",
- "panic-halt",
  "panic-probe",
- "static_cell",
  "usb-device",
  "usbd-uac2",
 ]
 
+[[package]]
+name = "maitake-sync"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d77c365d697828821727b9bc09e6bc3c518b8c63804e79e1be5a5ae091a7c5f"
+dependencies = [
+ "cordyceps",
+ "critical-section",
+ "loom",
+ "mutex-traits",
+ "mycelium-bitfield",
+ "pin-project",
+ "portable-atomic",
+ "tracing",
+]
+
+[[package]]
+name = "matchers"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d1525a2a28c7f4fa0fc98bb91ae755d1e2d1505079e05539e35bc876b5d65ae9"
+dependencies = [
+ "regex-automata",
+]
+
+[[package]]
+name = "memchr"
+version = "2.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8ca58f447f06ed17d5fc4043ce1b10dd205e060fb3ce5b979b8ed8e59ff3f79"
+
 [[package]]
 name = "modular-bitfield"
 version = "0.13.1"
@@ -392,6 +509,18 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "mutex-traits"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3929f2b5633d29cf7b6624992e5f3c1e9334f1193423e12d17be4faf678cde3f"
+
+[[package]]
+name = "mycelium-bitfield"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24e0cc5e2c585acbd15c5ce911dff71e1f4d5313f43345873311c4f5efd741cc"
+
 [[package]]
 name = "nb"
 version = "0.1.3"
@@ -407,6 +536,15 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8d5439c4ad607c3c23abf66de8c8bf57ba8adcd1f129e699851a6e43935d339d"
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys",
+]
+
 [[package]]
 name = "num"
 version = "0.3.1"
@@ -470,10 +608,10 @@ dependencies = [
 ]
 
 [[package]]
-name = "panic-halt"
+name = "once_cell"
-version = "1.0.0"
+version = "1.21.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a513e167849a384b7f9b746e517604398518590a9142f4846a32e3c2a4de7b11"
+checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
 
 [[package]]
 name = "panic-probe"
@@ -485,6 +623,32 @@ dependencies = [
  "defmt 1.0.1",
 ]
 
+[[package]]
+name = "pin-project"
+version = "1.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cbf0d9e68100b3a7989b4901972f265cd542e560a3a8a724e1e20322f4d06ce9"
+dependencies = [
+ "pin-project-internal",
+]
+
+[[package]]
+name = "pin-project-internal"
+version = "1.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a990e22f43e84855daf260dded30524ef4a9021cc7541c26540500a50b624389"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
 [[package]]
 name = "portable-atomic"
 version = "1.13.1"
@@ -537,6 +701,23 @@ version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
 
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
 [[package]]
 name = "rustc_version"
 version = "0.2.3"
@@ -561,6 +742,12 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
+[[package]]
+name = "scoped-tls"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1cf6437eb19a8f4a6cc0f7dca544973b0b78843adbfeb3683d1a94a0024a294"
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -588,6 +775,27 @@ version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
 
+[[package]]
+name = "sharded-slab"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40ca3c46823713e0d4209592e8d6e826aa57e928f09752619fc696c499637f6"
+dependencies = [
+ "lazy_static",
+]
+
+[[package]]
+name = "shlex"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
+
+[[package]]
+name = "smallvec"
+version = "1.15.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "67b1b7a3b5fe4f1376887184045fcf45c69e92af734b7aaddc05fb777b6fbd03"
+
 [[package]]
 name = "spin"
 version = "0.9.8"
@@ -609,15 +817,6 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 
-[[package]]
-name = "static_cell"
-version = "2.1.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0530892bb4fa575ee0da4b86f86c667132a94b74bb72160f58ee5a4afec74c23"
-dependencies = [
- "portable-atomic",
-]
-
 [[package]]
 name = "syn"
 version = "2.0.117"
@@ -649,6 +848,76 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thread_local"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f60246a4944f24f6e018aa17cdeffb7818b76356965d03b07d6a9886e8962185"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "tracing"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63e71662fa4b2a2c3a26f570f037eb95bb1f85397f3cd8076caed2f026a6d100"
+dependencies = [
+ "pin-project-lite",
+ "tracing-attributes",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-attributes"
+version = "0.1.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7490cfa5ec963746568740651ac6781f701c9c5ea257c58e057f3ba8cf69e8da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tracing-core"
+version = "0.1.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
+dependencies = [
+ "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.3.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb7f578e5945fb242538965c2d0b04418d38ec25c79d160cd279bf0731c8d319"
+dependencies = [
+ "matchers",
+ "nu-ansi-term",
+ "once_cell",
+ "regex-automata",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
+ "tracing",
+ "tracing-core",
+ "tracing-log",
+]
+
 [[package]]
 name = "typenum"
 version = "1.20.0"
@@ -684,6 +953,12 @@ dependencies = [
  "usb-device",
 ]
 
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
 [[package]]
 name = "vcell"
 version = "0.1.3"
@@ -710,3 +985,27 @@ checksum = "de437e2a6208b014ab52972a27e59b33fa2920d3e00fe05026167a1c509d19cc"
 dependencies = [
  "vcell",
 ]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-result"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7781fa89eaf60850ac3d2da7af8e5242a5ea78d1a11c49bf2910bb5a73853eb5"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]

examples/lpc55s28-evk/Cargo.toml

@@ -2,6 +2,7 @@
 name = "lpc55s28-evk"
 version = "0.1.0"
 edition = "2024"
+publish = false
 
 [features]
 default = ["usbhs"]
@@ -9,21 +10,19 @@ usbfs = []
 usbhs = []
 
 [dependencies]
+bbqueue = "0.7.0"
 cortex-m = { version = "0.7.7", features = ["critical-section-single-core"] }
 cortex-m-rt = "0.7.5"
 defmt = "1.0.1"
 defmt-rtt = "1.1.0"
 embedded-hal = "1.0.0"
 embedded-io = "0.7.1"
-heapless = "0.9.3"
 log-to-defmt = "0.1.0"
-lpc55-hal = { version = "0.5.0", path = "../lpc55-hal" }
-nb = "1.1.0"
-panic-halt = "1.0.0"
 panic-probe = { version = "1.0.0", features = ["print-defmt"] }
-static_cell = "2.1.1"
+# Includes update to usb-device 0.3, fix for isochronous and smaller critical sections
-usb-device = "0.3"
+lpc55-hal = { git = "https://github.com/ktims/lpc55-hal", branch = "main" }
-usbd-uac2 = { version = "0.1.0", path = "../..", features = ["defmt"]}
+usb-device.workspace = true
+usbd-uac2 = { workspace = true, features = ["defmt"] }
 
 [profile.release]
 opt-level = "z"

examples/lpc55s28-evk/build.rs

@@ -0,0 +1,5 @@
+// Find the actual path of memory.x and add it to link search, required for building in workspace
+fn main() {
+    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+    println!("cargo:rustc-link-search={}", manifest_dir);
+}

examples/lpc55s28-evk/src/hw.rs

@@ -1,8 +1,19 @@
 //! Contains hardware setup unrelated to Usb Audio Class implementation
 
 use crate::Syscon;
+use crate::hal;
 use crate::{MCLK_FREQ, SAMPLE_RATE, pac};
+
+use core::cell::UnsafeCell;
+use core::mem::MaybeUninit;
 use defmt::debug;
+use hal::{
+    Enabled, Iocon, Pin,
+    drivers::pins,
+    traits::wg::digital::v2::{OutputPin, ToggleableOutputPin},
+    typestates::pin::{gpio::direction::Output, state::Gpio},
+};
+
 pub(crate) struct PllConstants {
     pub m: u16,   // 1-65535
     pub n: u8,    // 1-255
@@ -79,7 +90,7 @@ pub(crate) fn init_audio_pll() {
         .xo32m_ctrl
         .modify(|_, w| w.enable_system_clk_out().enable());
 
-    debug!("init pll: {}", AUDIO_PLL);
+    debug!("init pll0: {}", AUDIO_PLL);
     pmc.pdruncfg0
         .modify(|_, w| w.pden_pll0().poweredoff().pden_pll0_sscg().poweredoff());
     syscon.pll0clksel.write(|w| w.sel().enum_0x1()); // clk_in
@@ -224,3 +235,74 @@ pub fn init_i2s(mut fc7: pac::FLEXCOMM7, i2s7: pac::I2S7, syscon: &mut Syscon) -
 
     I2sTx { i2s: regs }
 }
+
+pub struct SharedLed<T: OutputPin> {
+    inner: UnsafeCell<T>,
+}
+unsafe impl<T: OutputPin> Sync for SharedLed<T> {}
+impl<T: OutputPin> SharedLed<T> {
+    pub fn new(inner: T) -> Self {
+        Self {
+            inner: UnsafeCell::new(inner),
+        }
+    }
+    pub fn on(&self) {
+        unsafe {
+            (*self.inner.get()).set_low().ok();
+        }
+    }
+    pub fn off(&self) {
+        unsafe {
+            (*self.inner.get()).set_high().ok();
+        }
+    }
+}
+impl<T: OutputPin + ToggleableOutputPin> SharedLed<T> {
+    pub fn toggle(&self) {
+        unsafe {
+            (*self.inner.get()).toggle().ok();
+        }
+    }
+}
+
+type RedLed = Pin<pins::Pio1_6, Gpio<Output>>;
+type GreenLed = Pin<pins::Pio1_7, Gpio<Output>>;
+type BlueLed = Pin<pins::Pio1_4, Gpio<Output>>;
+pub static RED_LED: MaybeUninit<SharedLed<RedLed>> = MaybeUninit::uninit();
+pub static GREEN_LED: MaybeUninit<SharedLed<GreenLed>> = MaybeUninit::uninit();
+pub static BLUE_LED: MaybeUninit<SharedLed<BlueLed>> = MaybeUninit::uninit();
+
+pub fn init_leds(iocon: &mut Iocon<Enabled>, gpio: &mut hal::Gpio<Enabled>) {
+    let red_led = SharedLed::new(
+        pins::Pio1_6::take()
+            .unwrap()
+            .into_gpio_pin(iocon, gpio)
+            .into_output_low(),
+    );
+    let green_led = SharedLed::new(
+        pins::Pio1_7::take()
+            .unwrap()
+            .into_gpio_pin(iocon, gpio)
+            .into_output_low(),
+    );
+    let blue_led = SharedLed::new(
+        pins::Pio1_4::take()
+            .unwrap()
+            .into_gpio_pin(iocon, gpio)
+            .into_output_low(),
+    );
+    unsafe {
+        core::ptr::write(RED_LED.as_ptr() as *mut SharedLed<RedLed>, red_led);
+        core::ptr::write(GREEN_LED.as_ptr() as *mut SharedLed<GreenLed>, green_led);
+        core::ptr::write(BLUE_LED.as_ptr() as *mut SharedLed<BlueLed>, blue_led);
+    }
+}
+pub fn red_led() -> &'static SharedLed<RedLed> {
+    unsafe { &*RED_LED.as_ptr() }
+}
+pub fn green_led() -> &'static SharedLed<GreenLed> {
+    unsafe { &*GREEN_LED.as_ptr() }
+}
+pub fn blue_led() -> &'static SharedLed<BlueLed> {
+    unsafe { &*BLUE_LED.as_ptr() }
+}

examples/lpc55s28-evk/src/main.rs

@@ -1,10 +1,14 @@
-//! Interrupt driven example for the LPCXpresso55S28 demo board
+//! Interrupt driven example for the LPCXpresso55S28 demo board.
 //!
-//! Uses the onboard WM8904 DAC at 48KHz. Clock is generated by PLL0. Simple PI feedback
+//! This is a minimal implementation intended to demonstrate only the minimum
-//! is implemented.
+//! essential implementation, to clarify usage of the class driver.
 //!
-//! Packets from USB are placed a `heapless::spsc::Queue`. They are consumed
+//! Uses the EVK's WM8904 DAC at 48KHz. Clock is generated by PLL0. Simple
-//! by the I2S FIFO in the FLEXCOMM7 interrupt.
+//! proportional feedback is implemented.
+//!
+//! Packets from USB are placed in a `bbqueue`. They are consumed by the I2S
+//! FIFO in the FLEXCOMM7 interrupt. This makes the implementation very sensitive
+//! to interrupt::free critical sections (which are widely used in the USB bus driver)
 #![no_main]
 #![no_std]
 
@@ -17,8 +21,12 @@ fn panic() -> ! {
     panic_probe::hard_fault()
 }
 
-use core::ptr::null_mut;
+use bbqueue::{
-use core::sync::atomic::{AtomicBool, AtomicI32, Ordering};
+    nicknames::Churrasco,
+    prod_cons::stream::{StreamConsumer, StreamProducer},
+    traits::bbqhdl::BbqHandle,
+};
+use core::sync::atomic::{AtomicBool, AtomicU32, Ordering};
 use cortex_m_rt::entry;
 use defmt::debug;
 use defmt_rtt as _;
@@ -29,23 +37,18 @@ use hal::{
     prelude::*,
     time::Hertz,
 };
-use heapless::spsc::{Consumer, Producer, Queue};
+use lpc55_hal as hal;
-use lpc55_hal::{self as hal};
 use pac::interrupt;
-use static_cell::StaticCell;
 use usb_device::{
     bus::{self},
     device::{StringDescriptors, UsbDeviceBuilder, UsbVidPid},
-    endpoint::IsochronousSynchronizationType,
 };
-use usbd_uac2::UsbIsochronousFeedback;
 use usbd_uac2::{
-    self, AudioClassConfig, RangeEntry, TerminalConfig, UsbAudioClass, UsbAudioClockImpl, UsbSpeed,
+    self, AudioHandler, ClockSource, RangeEntry, TerminalConfig, UsbAudioClassConfig,
-    constants::{FunctionCode, TerminalType},
+    UsbIsochronousFeedback, UsbSpeed, constants::FunctionCode, descriptors::ClockType,
-    descriptors::{ChannelConfig, ClockType, FormatType1, LockDelay},
 };
 
-use crate::hw::I2sTx;
+use crate::hw::{I2sTx, blue_led, green_led, red_led};
 
 mod hw;
 mod wm8904;
@@ -53,58 +56,71 @@ mod wm8904;
 const CODEC_I2C_ADDR: u8 = 0b0011010;
 const FIFO_LENGTH: usize = 256; // frames
 const MCLK_FREQ: u32 = 12288000;
-const SAMPLE_RATE: u32 = 48000; // example implementation runs okay at 48k but not 96k
+const SAMPLE_RATE: u32 = 48000;
+// USB microframe rate
+#[cfg(feature = "usbhs")]
+const USB_FRAME_RATE: usize = 8000;
+#[cfg(feature = "usbfs")]
+const USB_FRAME_RATE: usize = 1000;
 type SampleType = (i32, i32);
 
-struct Clock {}
+const BYTES_PER_FRAME: usize = 8;
-impl Clock {
+const QUEUE_BYTES: usize = FIFO_LENGTH * BYTES_PER_FRAME;
-    const RATES: [RangeEntry<u32>; 1] = [RangeEntry::new_fixed(SAMPLE_RATE)];
+// We use bbqueue here for performance in the USB driver that runs almost entirely in interrupt free critical section.
-}
+static QUEUE: Churrasco<QUEUE_BYTES> = Churrasco::new();
-impl UsbAudioClockImpl for Clock {
+// Used for feedback calculation of current fifo state
-    const CLOCK_TYPE: usbd_uac2::descriptors::ClockType = ClockType::InternalFixed;
+static PRODUCED: AtomicU32 = AtomicU32::new(0);
-    const SOF_SYNC: bool = false;
+static CONSUMED: AtomicU32 = AtomicU32::new(0);
-    fn get_sample_rate(&self) -> core::result::Result<u32, usbd_uac2::UsbAudioClassError> {
-        Ok(Clock::RATES[0].min)
-    }
-    fn get_rates(
-        &self,
-    ) -> core::result::Result<&[usbd_uac2::RangeEntry<u32>], usbd_uac2::UsbAudioClassError> {
-        Ok(&Clock::RATES)
-    }
-    fn get_clock_validity(&self) -> core::result::Result<bool, usbd_uac2::UsbAudioClassError> {
-        Ok(true)
-    }
-}
 
-static FIFO_CONSUMER_STORE: StaticCell<Consumer<SampleType>> = StaticCell::new();
+#[inline]
-static mut FIFO_CONSUMER: *mut Consumer<SampleType> = null_mut();
+fn try_write_one_frame<T: BbqHandle>(
+    cons: &mut StreamConsumer<T>,
+    i2s: &pac::i2s7::RegisterBlock,
+) -> bool {
+    if let Ok(rgr) = cons.read() {
+        if rgr.len() >= BYTES_PER_FRAME {
+            let l = u32::from_le_bytes(rgr[0..4].try_into().unwrap());
+            let r = u32::from_le_bytes(rgr[4..8].try_into().unwrap());
+
+            i2s.fifowr.write(|w| unsafe { w.bits(l) });
+            i2s.fifowr.write(|w| unsafe { w.bits(r) });
+
+            // consume exactly one frame (8 bytes)
+            rgr.release(BYTES_PER_FRAME);
+            CONSUMED.fetch_add(BYTES_PER_FRAME as u32, Ordering::Relaxed);
+            return true;
+        } else {
+            // Not enough bytes for a full frame: leave it in the queue.
+            return false;
+        }
+    }
+    false
+}
 
 #[interrupt]
 fn FLEXCOMM7() {
     let i2s = unsafe { &*pac::I2S7::ptr() };
-
+    // refill until fifo has >6 words
-    // refil the buffer to 4 frames / 8 samples
+    let mut cons = QUEUE.stream_consumer();
-    let fifo = unsafe { &mut *FIFO_CONSUMER };
     while i2s.fifostat.read().txlvl().bits() <= 6 {
-        if let Some((l, r)) = fifo.dequeue() {
+        if !try_write_one_frame(&mut cons, i2s) {
-            i2s.fifowr.write(|w| unsafe { w.bits(l as u32) });
+            // No complete frame available: write silence to keep FIFO above threshold
-            i2s.fifowr.write(|w| unsafe { w.bits(r as u32) });
+            defmt::error!("underflow");
-        } else {
+            red_led().toggle();
-            // Queue underflow
-            defmt::error!("queue underflow");
             i2s.fifowr.write(|w| unsafe { w.bits(0) });
             i2s.fifowr.write(|w| unsafe { w.bits(0) });
+            break;
         }
     }
 }
 
-struct Audio<'a> {
+struct Audio<T: BbqHandle> {
     running: AtomicBool,
     i2s: I2sTx,
-    producer: Producer<'a, SampleType>,
+    producer: StreamProducer<T>,
-    integrator: AtomicI32,
 }
-impl<'a> Audio<'a> {
+impl<T: BbqHandle> Audio<T> {
+    const RATES: [RangeEntry<u32>; 1] = [RangeEntry::new_fixed(SAMPLE_RATE)];
     fn start(&self) {
         self.running.store(true, Ordering::Relaxed);
         defmt::info!("playback starting, enabling interrupts");
@@ -117,6 +133,7 @@ impl<'a> Audio<'a> {
         // FIFO level interrupt enable
         self.i2s.i2s.fifointenset.modify(|_, w| w.txlvl().enabled());
         unsafe { pac::NVIC::unmask(pac::Interrupt::FLEXCOMM7) };
+        green_led().on();
     }
     fn stop(&self) {
         // If we don't disable interrupts while stopped, we will underflow constantly and continuously refill the fifo with 0s
@@ -125,9 +142,26 @@ impl<'a> Audio<'a> {
         self.running.store(true, Ordering::Relaxed);
         defmt::info!("playback stopped");
         pac::NVIC::mask(pac::Interrupt::FLEXCOMM7);
+        green_led().off();
     }
 }
-impl<'a, B: bus::UsbBus> UsbAudioClass<'a, B> for Audio<'_> {
+
+impl<T: BbqHandle> ClockSource for Audio<T> {
+    const CLOCK_TYPE: usbd_uac2::descriptors::ClockType = ClockType::InternalFixed;
+    const SOF_SYNC: bool = false;
+    fn sample_rate(&self) -> u32 {
+        Self::RATES[0].min
+    }
+    fn sample_rates(
+        &self,
+    ) -> core::result::Result<&[usbd_uac2::RangeEntry<u32>], usbd_uac2::UsbAudioClassError> {
+        Ok(&Self::RATES)
+    }
+    fn clock_validity(&self) -> core::result::Result<bool, usbd_uac2::UsbAudioClassError> {
+        Ok(true)
+    }
+}
+impl<T: BbqHandle, B: bus::UsbBus> AudioHandler<'_, B> for Audio<T> {
     fn alternate_setting_changed(&mut self, _terminal: usb_device::UsbDirection, alt_setting: u8) {
         // alt setting 0 means stopped
         match alt_setting {
@@ -138,10 +172,13 @@ impl<'a, B: bus::UsbBus> UsbAudioClass<'a, B> for Audio<'_> {
     }
     fn audio_data_rx(
         &mut self,
-        ep: &usb_device::endpoint::Endpoint<'a, B, usb_device::endpoint::Out>,
+        ep: &usb_device::endpoint::Endpoint<'_, B, usb_device::endpoint::Out>,
     ) {
-        // Buffer must fit 1ms of audio data (based on how `usbd_uac2` sets up the descriptors), calculate that size here.
+        // Buffer must fit one microframe's (125us @ HS, 1ms @ FS) of audio data
-        let mut buf = [0; SAMPLE_RATE as usize / 1000 * core::mem::size_of::<SampleType>()];
+        // (based on how `usbd_uac2` sets up the descriptors), calculate that
+        // size here.
+        let mut buf =
+            [0; (SAMPLE_RATE as usize / USB_FRAME_RATE + 1) * core::mem::size_of::<SampleType>()];
         let len = match ep.read(&mut buf) {
             Ok(len) => len,
             Err(_) => {
@@ -150,65 +187,44 @@ impl<'a, B: bus::UsbBus> UsbAudioClass<'a, B> for Audio<'_> {
             }
         };
         let buf = &buf[..len];
-        // Translate the raw USB data into audio frames
+
-        for sample in buf
+        if let Ok(mut wg) = self.producer.grant_exact(buf.len()) {
-            .chunks_exact(core::mem::size_of::<SampleType>())
+            wg.copy_from_slice(buf);
-            .map(|b| {
+            wg.commit(buf.len());
-                // TODO: implement SampleType::from
+            PRODUCED.fetch_add(buf.len() as u32, Ordering::Relaxed);
-                (
+        } else {
-                    i32::from_le_bytes(b[..4].try_into().unwrap()),
+            blue_led().on();
-                    i32::from_le_bytes(b[4..].try_into().unwrap()),
+            defmt::error!("overflowed bbq, asked {}", buf.len());
-                )
-            })
-        {
-            if self.producer.enqueue(sample).is_err() {
-                defmt::error!("overflowed fifo, len: {}", self.producer.len());
-            }
         }
     }
 
     /// Provide rate feedback to the host, so that it doesn't over- or underflow
-    /// our queue.
+    /// our queue. This implementation is not tuned.
-    fn feedback(&mut self) -> Option<UsbIsochronousFeedback> {
+    fn feedback(&mut self, nominal_rate: UsbIsochronousFeedback) -> Option<UsbIsochronousFeedback> {
-        // Samples per USB interval (1ms)
+        let target = FIFO_LENGTH as i32 / 2;
-        const FRAME_SAMPLES: i32 = SAMPLE_RATE as i32 / 1000;
 
-        // Keep FIFO around half full, minus one USB packet worth
+        let fill = PRODUCED
-        const TARGET: i32 = FIFO_LENGTH as i32 / 2 - FRAME_SAMPLES;
+            .load(Ordering::Acquire)
+            .wrapping_sub(CONSUMED.load(Ordering::Acquire)) as i32
+            / BYTES_PER_FRAME as i32;
 
-        // 16.16 fixed-point nominal feedback value
+        let error = fill - target;
-        const NOMINAL: i32 = FRAME_SAMPLES << 16;
+        // Clamp excursions.
-        const MAX_ERROR: i32 = FRAME_SAMPLES / 2;
+        let (i, _f) = nominal_rate.parts();
+        let error = error.clamp(-(i as i32 * 4), i as i32 * 4);
 
-        let queuelen = self.producer.len() as i32;
+        let p = error << 8;
 
-        let error = (queuelen - TARGET).clamp(-MAX_ERROR, MAX_ERROR);
+        let correction = -p;
+        let nominal_v = nominal_rate.to_u32_12_13() as i32;
 
-        // slow down accumulation of I
+        let mut v = nominal_v + correction;
-        const I_ACCUM_DIV: i32 = 8;
-        let i_delta = error / I_ACCUM_DIV;
-        let integrator = self.integrator.fetch_add(i_delta, Ordering::Relaxed) + i_delta;
 
-        // Integrator saturates at 1024xFRAME_SAMPLES
+        // Clamp corrections
-        let i_limit = FRAME_SAMPLES << 10;
+        v = v.clamp(nominal_v - (1 << 14), nominal_v + (1 << 14));
-        let integrator = integrator.clamp(-i_limit, i_limit);
 
-        // Gains
+        // Note: this log will cause continuous underflows
-        let p = error << 7;
+        defmt::debug!("fill:{} err:{} fb:{=u32:x}", fill, error, v as u32);
-        let i = integrator << 3;
-
-        // Total correction in 16.16 space
-        let correction = -(p + i);
-
-        let v = NOMINAL + correction;
-
-        defmt::debug!(
-            "q:{} err:{} i:{} fb:{}",
-            queuelen,
-            error,
-            integrator,
-            v >> 16
-        );
 
         Some(UsbIsochronousFeedback::new(v as u32))
     }
@@ -227,10 +243,7 @@ fn main() -> ! {
 
     debug!("start");
 
-    let mut red_led = pins::Pio1_6::take()
+    hw::init_leds(&mut iocon, &mut gpio);
-        .unwrap()
-        .into_gpio_pin(&mut iocon, &mut gpio)
-        .into_output_low(); // start turned off
 
     debug!("iocon");
     let usb0_vbus_pin = pins::Pio0_22::take()
@@ -249,7 +262,6 @@ fn main() -> ! {
     );
 
     debug!("clocks");
-    // Run the system clock at 96MHz. The lpc55-hal will run it from the FRO.
     let clocks = hal::ClockRequirements::default()
         .system_frequency(96.MHz())
         .configure(&mut anactrl, &mut pmc, &mut syscon)
@@ -280,58 +292,43 @@ fn main() -> ! {
     };
 
     #[cfg(feature = "usbhs")]
-    let usb_peripheral = hal.usbhs.enabled_as_device(
+    let (usb_speed, usb_peripheral) = (
-        &mut anactrl,
+        UsbSpeed::High,
-        &mut pmc,
+        hal.usbhs.enabled_as_device(
-        &mut syscon,
+            &mut anactrl,
-        &mut _delay_timer,
+            &mut pmc,
-        clocks.support_usbhs_token().unwrap(),
+            &mut syscon,
+            &mut _delay_timer,
+            clocks.support_usbhs_token().unwrap(),
+        ),
     );
     #[cfg(feature = "usbfs")]
-    let usb_peripheral = hal.usbfs.enabled_as_device(
+    let (usb_speed, usb_peripheral) = (
-        &mut anactrl,
+        UsbSpeed::Full,
-        &mut pmc,
+        hal.usbfs.enabled_as_device(
-        &mut syscon,
+            &mut anactrl,
-        clocks.support_usbfs_token().unwrap(),
+            &mut pmc,
+            &mut syscon,
+            clocks.support_usbfs_token().unwrap(),
+        ),
     );
 
     let usb_bus = UsbBus::new(usb_peripheral, usb0_vbus_pin);
 
     defmt::debug!("codec init");
     wm8904::init_codec(&mut i2c_bus);
-    let queue = cortex_m::singleton!(
-        : Queue<SampleType, FIFO_LENGTH>
-        = Queue::new()
-    )
-    .unwrap();
-    let (producer, consumer) = queue.split();
 
-    let consumer_ref = FIFO_CONSUMER_STORE.init(consumer);
+    // let consumer_ref = FIFO_CONSUMER_STORE.init(consumer);
-    unsafe { FIFO_CONSUMER = consumer_ref as *mut _ };
+    // unsafe { FIFO_CONSUMER = consumer_ref as *mut _ };
 
-    let mut clock = Clock {};
     let mut audio = Audio {
         i2s: i2s_peripheral,
-        producer,
+        producer: QUEUE.stream_producer(),
         running: AtomicBool::new(false),
-        integrator: AtomicI32::new(0),
     };
 
-    let config = AudioClassConfig::new(UsbSpeed::High, FunctionCode::Other, &mut clock, &mut audio)
+    let config = UsbAudioClassConfig::new(usb_speed, FunctionCode::IoBox, &mut audio)
-        .with_output_config(TerminalConfig::new(
+        .with_output_config(TerminalConfig::builder().base_id(2).build());
-            4,
-            1,
-            2,
-            FormatType1 {
-                bit_resolution: 32,
-                bytes_per_sample: 4,
-            },
-            TerminalType::ExtLineConnector,
-            ChannelConfig::default_chans(2),
-            IsochronousSynchronizationType::Asynchronous,
-            LockDelay::Milliseconds(10),
-            None,
-        ));
 
     let mut uac2 = config.build(&usb_bus).unwrap();
 
@@ -353,6 +350,5 @@ fn main() -> ! {
 
     loop {
         usb_dev.poll(&mut [&mut uac2]);
-        red_led.set_high().ok(); // Turn off
     }
 }

src/lib.rs

@@ -8,24 +8,18 @@ mod log;
 
 use core::cmp::Ordering;
 use core::marker::PhantomData;
-use core::sync::atomic::AtomicUsize;
 
 use byteorder_embedded_io::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use constants::*;
 use descriptors::*;
 use log::*;
 
-use num_traits::ConstZero;
+use num_traits::{ConstZero, ToPrimitive};
 use usb_device::control::{Recipient, Request, RequestType};
 use usb_device::device::DEFAULT_ALTERNATE_SETTING;
 use usb_device::endpoint::{self, Endpoint, EndpointDirection, In, Out};
 use usb_device::{UsbDirection, class_prelude::*};
 
-pub use constants::USB_CLASS_AUDIO;
-
-#[cfg(feature = "defmt")]
-use defmt;
-
 mod sealed {
     pub trait Sealed {}
 }
@@ -66,6 +60,9 @@ impl RangeType for u8 {}
 impl RangeType for u16 {}
 impl RangeType for u32 {}
 
+/// Represent a range request/response.
+///
+/// ref: UAC2 5.2.2
 #[derive(PartialEq, Eq, Ord)]
 pub struct RangeEntry<T: RangeType> {
     pub min: T,
@@ -85,10 +82,7 @@ impl<T: RangeType> RangeEntry<T> {
         }
     }
 
-    pub fn write<W: embedded_io::Write>(
+    fn write<W: embedded_io::Write>(&self, mut buf: W) -> core::result::Result<usize, W::Error> {
-        &self,
-        mut buf: W,
-    ) -> core::result::Result<usize, W::Error> {
         buf.write_all(self.min.to_le_bytes().as_ref())?;
         buf.write_all(self.max.to_le_bytes().as_ref())?;
         buf.write_all(self.res.to_le_bytes().as_ref())?;
@@ -96,48 +90,42 @@ impl<T: RangeType> RangeEntry<T> {
     }
 }
 
-/// The spec guarantees that ranges do not overlap, so compare by min is correct.
+// The spec guarantees that ranges do not overlap, so compare by min is correct.
 impl<T: RangeType + PartialOrd> PartialOrd for RangeEntry<T> {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         self.min.partial_cmp(&other.min)
     }
 }
 
-/// Fixed point 10.14, packed to the least significant 3-bytes of a 4-byte USB feedback endpoint response
+/// Represent Isochronous feedback as integer and fractional parts, internally as 16.16.
+///
+/// Provides conversions to and from the different USB formats.
 #[derive(Copy, Clone)]
-pub struct UsbIsochronousFeedback {
+pub struct UsbIsochronousFeedback(u32);
-    pub int: u16,
-    pub frac: u16,
-}
 
 impl UsbIsochronousFeedback {
+    pub fn new(v: u32) -> Self {
+        Self(v)
+    }
     /// Accepts all u16 values, saturating the output depending on format
     pub fn new_frac(int: u16, frac: u16) -> Self {
-        Self { int, frac }
+        Self(((int as u32) << 16) | frac as u32)
     }
-    /// Assumed 16.16, not either of the USB formats
+    /// Convert float to fixed point
-    pub fn new(value: u32) -> Self {
+    pub fn new_float(rate: f32) -> Self {
-        Self {
+        let fb = (rate * 65536.0 + 0.5) as u32;
-            int: (value >> 16) as u16,
+        Self(fb)
-            frac: (value & 0xffff) as u16,
+    }
-        }
+    pub fn parts(&self) -> (u16, u16) {
+        ((self.0 >> 16) as u16, (self.0 & 0xffff) as u16)
     }
     /// Serialize into a u32 in 16.16 representation for USB HS
     pub fn to_u32_12_13(&self) -> u32 {
-        let int = (self.int as u32) << 16;
+        self.0
-        // ostensibly 13 bits, so should require << 3, but USB allows us to use
-        // these bits for 'extra precision'. So we may as well just treat it as
-        // 16.16. The application can << 3 if it wants to for some reason.
-        let frac = (self.frac as u32) & 0xffff;
-
-        int | frac
     }
-    /// Serialize into a u32 in 10.14 representation for USB FS (take the 3 LSB)
+    /// Serialize into a u32 in 10.14 representation for USB FS
     pub fn to_u32_10_14(&self) -> u32 {
-        let int = (self.int as u32) << 14;
+        (self.0 + 2) >> 2
-        let frac = (self.frac as u32) & 0x3fff;
-
-        int | frac
     }
     /// Serialize into 16.16 little endian byte array for USB HS
     pub fn to_bytes_12_13(&self) -> [u8; 4] {
@@ -152,16 +140,11 @@ impl UsbIsochronousFeedback {
 
 /// A trait for implementing USB Audio Class 2 devices
 ///
-/// Contains callback methods which will be called by the class driver. All
+/// Contains callback methods which will be called by the class driver.
-/// callbacks are optional, which may be useful for a tight-loop polling implementation
+pub trait AudioHandler<'a, B: UsbBus> {
-/// but most implementations will want to implement at least `audio_data_rx`.
-///
-/// Unimplemented callbacks should return `Ok(())` if a result is required.
-
-pub trait UsbAudioClass<'a, B: UsbBus> {
     /// Called when audio data is received from the host. `ep` is ready for
     /// `ep.read()`.
-    fn audio_data_rx(&mut self, ep: &Endpoint<'a, B, endpoint::Out>) {}
+    fn audio_data_rx(&mut self, ep: &Endpoint<'a, B, endpoint::Out>);
 
     /// Called when it's time to send an isochronous feedback update. Should
     /// return the correct feedback payload. Feedback always runs at 1ms (in
@@ -169,14 +152,15 @@ pub trait UsbAudioClass<'a, B: UsbBus> {
     ///
     /// Required for isochronous asynchronous mode to work properly. If None is
     /// returned, no IN packet will be emitted at feedback time.
-    fn feedback(&mut self, nominal_rate: UsbIsochronousFeedback) -> Option<UsbIsochronousFeedback> {
+    fn feedback(&mut self, nominal: UsbIsochronousFeedback) -> Option<UsbIsochronousFeedback>;
-        None
-    }
 
     /// Called when the alternate setting of `terminal`'s interface is changed,
-    /// before the `AudioStream` is updated. Currently not very useful since we
+    /// before the `AudioStream` is updated. This is how the host signals start/stop
-    /// don't implement alternate settings.
+    /// of audio streaming. We do not expect audio frames when alt setting is 0.
-    fn alternate_setting_changed(&mut self, terminal: UsbDirection, alt_setting: u8) {}
+    ///
+    /// The implementation will also call `alternate_setting_changed(_, 0)` when
+    /// the host disconnects / resets.
+    fn alternate_setting_changed(&mut self, terminal: UsbDirection, alt_setting: u8);
 }
 
 /// A trait for implementing Sampling Frequency Control for USB Audio Clock Sources
@@ -187,7 +171,7 @@ pub trait UsbAudioClass<'a, B: UsbBus> {
 /// Unimplemented callbacks should return `Err(UsbAudioClassError::NotImplemented)`. Other
 /// errors will panic (the underlying callbacks are not fallible). If you need to handle errors,
 /// you should use the callback to infalliably signal another task.
-pub trait UsbAudioClockImpl {
+pub trait ClockSource {
     const CLOCK_TYPE: ClockType;
     const SOF_SYNC: bool;
     /// Called when the host or class needs the current sample rate. Returns the
@@ -196,7 +180,7 @@ pub trait UsbAudioClockImpl {
     ///
     /// Should never return 0 as it may be used in divides in the feedback loop
     /// and that would cause a hard fault.
-    fn get_sample_rate(&self) -> u32;
+    fn sample_rate(&self) -> u32;
     /// Called when the host requests to set the sample rate. Not necessarily called at all startups,
     /// so alt_setting should start/stop the clock. Not required for 'fixed' clocks.
     fn set_sample_rate(
@@ -207,14 +191,14 @@ pub trait UsbAudioClockImpl {
     }
     /// Called when the host requests to get the clock validity. Returns `true`
     /// if the clock is stable and on frequency.
-    fn get_clock_validity(&self) -> core::result::Result<bool, UsbAudioClassError> {
+    fn clock_validity(&self) -> core::result::Result<bool, UsbAudioClassError> {
         Err(UsbAudioClassError::NotImplemented)
     }
     /// Called during descriptor construction to describe if the clock validity can be read (write is not valid).
     ///
     /// By default will call `get_clock_validity` to determine if the clock validity can be read.
-    fn get_validity_access(&self) -> core::result::Result<bool, UsbAudioClassError> {
+    fn clock_validity_access(&self) -> core::result::Result<bool, UsbAudioClassError> {
-        match self.get_clock_validity() {
+        match self.clock_validity() {
             Ok(_) => Ok(true),
             Err(UsbAudioClassError::NotImplemented) => Ok(false),
             Err(err) => Err(err),
@@ -232,35 +216,29 @@ pub trait UsbAudioClockImpl {
     ///     its MIN and MAX subattribute and the RES subattribute must be set to zero
     ///
     /// ref: USB Audio Class Specification 2.0 5.2.1 & 5.2.3.3
-    fn get_rates(&self) -> core::result::Result<&[RangeEntry<u32>], UsbAudioClassError>;
+    fn sample_rates(&self) -> core::result::Result<&[RangeEntry<u32>], UsbAudioClassError>;
 
-    /// Called when the audio device's AltSetting is changed. Usually 0 signals shutdown of the
+    /// Build the ClockSource descriptor. It is not intended to override this
-    /// streaming audio and 1 signals start of streaming. This should be used to start the clock
+    /// method, but provided so you can.
-    /// (and stop it if desired). If unimplemented, does nothing - keep the clock running at all times.
-    fn alt_setting(&mut self, alt_setting: u8) -> core::result::Result<(), UsbAudioClassError> {
-        Ok(())
-    }
-
-    /// Build the ClockSource descriptor. It is not intended to override this method.
     ///
     /// Assumes access control based on clock type. Internal fixed/variable are read only,
     /// external and internal programmable are programmable.
-    fn get_configuration_descriptor(
+    fn clock_configuration_descriptor(
         &self,
         id: u8,
         string: Option<StringIndex>,
-    ) -> usb_device::Result<ClockSource> {
+    ) -> usb_device::Result<descriptors::ClockSource> {
         let frequency_access = match Self::CLOCK_TYPE {
             ClockType::InternalFixed | ClockType::InternalVariable => AccessControl::ReadOnly,
             ClockType::External | ClockType::InternalProgrammable => AccessControl::Programmable,
         };
-        let validity_access = match self.get_validity_access() {
+        let validity_access = match self.clock_validity_access() {
             Ok(true) => AccessControl::ReadOnly,
             Ok(false) | Err(UsbAudioClassError::NotImplemented) => AccessControl::NotPresent,
             _ => return Err(UsbError::Unsupported),
         };
 
-        let cs = ClockSource {
+        let cs = descriptors::ClockSource {
             id: id,
             clock_type: Self::CLOCK_TYPE,
             sof_sync: Self::SOF_SYNC,
@@ -278,6 +256,102 @@ trait TerminalConfigurationDescriptors {
     fn get_configuration_descriptors(&self) -> (InputTerminal, OutputTerminal);
 }
 
+pub struct TerminalConfigBuilder<D: EndpointDirection> {
+    base_id: Option<u8>,
+    clock_source_id: Option<u8>,
+    num_channels: Option<u8>,
+    format: Option<FormatType1>,
+    terminal_type: Option<TerminalType>,
+    channel_config: Option<ChannelConfig>,
+    sync_type: Option<IsochronousSynchronizationType>,
+    lock_delay: Option<LockDelay>,
+    string: Option<StringIndex>,
+    _direction: PhantomData<D>,
+}
+
+// Global builder initialization defaults
+impl<D: EndpointDirection> TerminalConfigBuilder<D> {
+    fn new() -> Self {
+        Self {
+            base_id: None,
+            clock_source_id: None,
+            num_channels: None,
+            format: None,
+            terminal_type: None,
+            channel_config: None,
+            sync_type: None,
+            lock_delay: None,
+            string: None,
+            _direction: PhantomData,
+        }
+    }
+
+    pub fn base_id(mut self, id: u8) -> Self {
+        self.base_id = Some(id);
+        self
+    }
+
+    pub fn clock_source_id(mut self, id: u8) -> Self {
+        self.clock_source_id = Some(id);
+        self
+    }
+
+    pub fn num_channels(mut self, channels: u8) -> Self {
+        self.num_channels = Some(channels);
+        self
+    }
+
+    pub fn format(mut self, format: FormatType1) -> Self {
+        self.format = Some(format);
+        self
+    }
+
+    pub fn terminal_type(mut self, t: TerminalType) -> Self {
+        self.terminal_type = Some(t);
+        self
+    }
+
+    pub fn channel_config(mut self, config: ChannelConfig) -> Self {
+        self.channel_config = Some(config);
+        self
+    }
+
+    pub fn sync_type(mut self, sync: IsochronousSynchronizationType) -> Self {
+        self.sync_type = Some(sync);
+        self
+    }
+
+    pub fn lock_delay(mut self, delay: LockDelay) -> Self {
+        self.lock_delay = Some(delay);
+        self
+    }
+
+    pub fn string(mut self, index: StringIndex) -> Self {
+        self.string = Some(index);
+        self
+    }
+
+    pub fn build(self) -> TerminalConfig<D> {
+        TerminalConfig {
+            base_id: self.base_id.expect("base_id is required"),
+            clock_source_id: self.clock_source_id.unwrap_or(1),
+            num_channels: self.num_channels.unwrap_or(2),
+            format: self.format.unwrap_or(FormatType1 {
+                bytes_per_sample: 4,
+                bit_resolution: 32,
+            }),
+            terminal_type: self.terminal_type.unwrap_or(TerminalType::ExtUndefined),
+            channel_config: self
+                .channel_config
+                .unwrap_or(ChannelConfig::default_chans(self.num_channels.unwrap_or(2))),
+            sync_type: IsochronousSynchronizationType::Asynchronous,
+            lock_delay: LockDelay::Undefined(0),
+            string: self.string, // Implicitly handles None or Option mapping
+            _direction: PhantomData,
+        }
+    }
+}
+
 pub struct TerminalConfig<D: EndpointDirection> {
     /// USB terminal in the D direction will have this id, audio terminal will have this id + 1
     base_id: u8,
@@ -292,9 +366,8 @@ pub struct TerminalConfig<D: EndpointDirection> {
     _direction: PhantomData<D>,
 }
 
-// TODO: builder pattern
 impl<D: EndpointDirection> TerminalConfig<D> {
-    pub fn new(
+    fn new(
         base_id: u8,
         clock_source_id: u8,
         num_channels: u8,
@@ -322,6 +395,10 @@ impl<D: EndpointDirection> TerminalConfig<D> {
     pub fn bytes_per_frame(&self) -> u32 {
         self.format.bytes_per_sample as u32 * self.num_channels as u32
     }
+
+    pub fn builder() -> TerminalConfigBuilder<D> {
+        TerminalConfigBuilder::new()
+    }
 }
 impl<'a> TerminalConfigurationDescriptors for TerminalConfig<Out> {
     fn get_configuration_descriptors(&self) -> (InputTerminal, OutputTerminal) {
@@ -422,10 +499,9 @@ pub enum UsbSpeed {
 /// A single Clock Source is always required, but a fully custom descriptor set can be built by only providing
 /// the Clock Source and additional descriptors, if the Terminal descriptors are inappropriate.
 ///
-pub struct AudioClassConfig<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> {
+pub struct UsbAudioClassConfig<'a, B: UsbBus, AU: AudioHandler<'a, B> + ClockSource> {
     pub speed: UsbSpeed,
     pub device_category: FunctionCode,
-    pub clock_impl: &'a mut CS,
     pub audio_impl: &'a mut AU,
     pub input_config: Option<TerminalConfig<In>>,
     pub output_config: Option<TerminalConfig<Out>>,
@@ -433,19 +509,11 @@ pub struct AudioClassConfig<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioCl
     _bus: PhantomData<B>,
 }
 
-impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
+impl<'a, B: UsbBus, AU: AudioHandler<'a, B> + ClockSource> UsbAudioClassConfig<'a, B, AU> {
-    AudioClassConfig<'a, B, CS, AU>
+    pub fn new(speed: UsbSpeed, device_category: FunctionCode, audio_impl: &'a mut AU) -> Self {
-{
-    pub fn new(
-        speed: UsbSpeed,
-        device_category: FunctionCode,
-        clock_impl: &'a mut CS,
-        audio_impl: &'a mut AU,
-    ) -> Self {
         Self {
             speed,
             device_category,
-            clock_impl,
             audio_impl,
             input_config: None,
             output_config: None,
@@ -470,7 +538,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
     }
 
     /// Allocate the various USB IDs, and build the class implementation
-    pub fn build(self, alloc: &'a UsbBusAllocator<B>) -> Result<AudioClass<'a, B, CS, AU>> {
+    pub fn build(self, alloc: &'a UsbBusAllocator<B>) -> Result<UsbAudioClass<'a, B, AU>> {
         let speed = self.speed;
         let (interval, fb_interval, audio_rate) = match speed {
             UsbSpeed::Full => (1, 1, 1000),
@@ -478,8 +546,8 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
             UsbSpeed::Low => return Err(Error::InvalidSpeed),
         };
         let max_rate = self
-            .clock_impl
+            .audio_impl
-            .get_rates()
+            .sample_rates()
             .unwrap()
             .iter()
             .max()
@@ -487,9 +555,12 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
             .max;
         let control_iface = alloc.interface();
 
-        let mut ac = AudioClass {
+        let nominal_fb = UsbIsochronousFeedback::new_float(
+            self.audio_impl.sample_rate().to_f32().unwrap() / audio_rate.to_f32().unwrap(),
+        );
+
+        let mut ac = UsbAudioClass {
             control_iface,
-            clock_impl: self.clock_impl,
             audio_impl: self.audio_impl,
             output: None,
             input: None,
@@ -502,6 +573,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
             out_ep: 0,
             fb_ep: 0,
             speed,
+            nominal_fb,
             audio_rate,
         };
 
@@ -510,7 +582,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
             let endpoint = alloc.isochronous(
                 config.sync_type,
                 IsochronousUsageType::Data,
-                (max_rate.div_ceil(audio_rate) * config.bytes_per_frame()) as u16,
+                ((max_rate.div_ceil(audio_rate) + 1) * config.bytes_per_frame()) as u16, // headroom of 1 sample for rate control
                 interval,
             );
             let feedback_ep = alloc.isochronous(
@@ -537,7 +609,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>>
             let endpoint = alloc.isochronous(
                 config.sync_type,
                 IsochronousUsageType::Data,
-                (max_rate.div_ceil(audio_rate) * config.bytes_per_frame()) as u16,
+                ((max_rate.div_ceil(audio_rate) + 1) * config.bytes_per_frame()) as u16, // headroom of 1 sample for rate control
                 interval,
             );
             let alt_setting = DEFAULT_ALTERNATE_SETTING;
@@ -654,9 +726,8 @@ impl<'a, B: UsbBus, D: EndpointDirection> AudioStream<'a, B, D> {
     }
 }
 
-pub struct AudioClass<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> {
+pub struct UsbAudioClass<'a, B: UsbBus, AU: AudioHandler<'a, B> + ClockSource> {
     control_iface: InterfaceNumber,
-    clock_impl: &'a mut CS,
     audio_impl: &'a mut AU,
     output: Option<AudioStream<'a, B, Out>>,
     input: Option<AudioStream<'a, B, In>>,
@@ -669,11 +740,12 @@ pub struct AudioClass<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a
     out_ep: usize,
     fb_ep: usize,
     speed: UsbSpeed,
+    nominal_fb: UsbIsochronousFeedback,
     audio_rate: u32, // audio packet rate in hz
 }
 
-impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> UsbClass<B>
+impl<'a, B: UsbBus, AU: AudioHandler<'a, B> + ClockSource> UsbClass<B>
-    for AudioClass<'a, B, CS, AU>
+    for UsbAudioClass<'a, B, AU>
 {
     fn get_configuration_descriptors(
         &self,
@@ -705,7 +777,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> UsbClass<B>
 
         // BUILD CONFIGURATION DESCRIPTORS //
         let mut total_length: u16 = 9; // HEADER
-        let clock_desc = self.clock_impl.get_configuration_descriptor(1, None)?;
+        let clock_desc = self.audio_impl.clock_configuration_descriptor(1, None)?;
         total_length += clock_desc.size() as u16;
         let output_descs = match &self.output {
             Some(stream) => {
@@ -811,39 +883,25 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> UsbClass<B>
     }
     fn endpoint_out(&mut self, addr: EndpointAddress) {
         debug!("EP {} out data", addr);
-        static COUNTER: AtomicUsize = AtomicUsize::new(0);
         if addr.index() == self.out_ep {
             self.audio_impl
                 .audio_data_rx(&self.output.as_ref().unwrap().endpoint);
-            let new_count = COUNTER.fetch_add(1, core::sync::atomic::Ordering::Relaxed);
-
-            if let Some(fb_ep) = self.feedback.as_ref() {
-                if new_count.is_multiple_of(1 << (fb_ep.interval() - 1) as usize) {
-                    let cur_rate = self.clock_impl.get_sample_rate();
-                    let numerator = (cur_rate as u64) << 16;
-                    let raw = (numerator + self.audio_rate as u64 / 2) / (self.audio_rate as u64);
-                    let nominal_rate = UsbIsochronousFeedback {
-                        int: (raw >> 16) as u16,
-                        frac: (raw & 0xffff) as u16,
-                    };
-
-                    if let Some(fb) = self.audio_impl.feedback(nominal_rate) {
-                        debug!("  emitting feedback IN {:08x}", fb.to_u32_12_13());
-                        let r = match self.speed {
-                            UsbSpeed::Low | UsbSpeed::Full => fb_ep.write(&fb.to_bytes_10_14()),
-                            UsbSpeed::High | UsbSpeed::Super => fb_ep.write(&fb.to_bytes_12_13()),
-                        };
-                        if let Err(e) = r {
-                            warn!("  feedback IN failed {:?}", e);
-                        }
-                    }
-                }
-            }
         } else {
             debug!("  unexpected OUT on {}", addr);
         }
     }
 
+    fn endpoint_in_complete(&mut self, addr: EndpointAddress) {
+        debug!("EP {} IN complete", addr);
+        if let Some(fb_ep) = self.feedback.as_ref()
+            && addr.index() == self.fb_ep
+        {
+            self.emit_feedback();
+        } else {
+            debug!("  unexpected IN on {}", addr);
+        }
+    }
+
     fn poll(&mut self) {
         debug!("poll");
         // no streaming in alt 0
@@ -871,9 +929,33 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> UsbClass<B>
             }
         }
     }
+
+    fn reset(&mut self) {
+        info!("usb reset");
+        self.audio_impl
+            .alternate_setting_changed(UsbDirection::In, 0);
+        self.audio_impl
+            .alternate_setting_changed(UsbDirection::Out, 0);
+    }
 }
 
-impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<'a, B, CS, AU> {
+impl<'a, B: UsbBus, AU: AudioHandler<'a, B> + ClockSource> UsbAudioClass<'a, B, AU> {
+    fn emit_feedback(&mut self) {
+        if let Some(fb_ep) = self.feedback.as_ref() {
+            if let Some(fb) = self.audio_impl.feedback(self.nominal_fb) {
+                debug!("  emitting feedback IN {:08x}", fb.to_u32_12_13());
+                let r = match self.speed {
+                    UsbSpeed::Low | UsbSpeed::Full => fb_ep.write(&fb.to_bytes_10_14()),
+                    UsbSpeed::High | UsbSpeed::Super => fb_ep.write(&fb.to_bytes_12_13()),
+                };
+                if let Err(e) = r {
+                    warn!("  feedback IN failed {:?}", e);
+                }
+            } else {
+                debug!("  feedback callback returned None");
+            }
+        }
+    }
     fn standard_request_out(&mut self, xfer: ControlOut<B>) {
         let req = xfer.request();
         match (req.recipient, req.request) {
@@ -933,7 +1015,6 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
         if self.input.is_some() && iface == self.in_iface {
             let old_alt = self.input.as_ref().unwrap().alt_setting;
             if old_alt != alt_setting {
-                self.clock_impl.alt_setting(alt_setting).ok();
                 self.audio_impl
                     .alternate_setting_changed(UsbDirection::In, alt_setting);
                 self.input.as_mut().unwrap().alt_setting = alt_setting;
@@ -942,9 +1023,10 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
         } else if self.output.is_some() && iface == self.out_iface {
             let old_alt = self.output.as_ref().unwrap().alt_setting;
             if old_alt != alt_setting {
-                self.clock_impl.alt_setting(alt_setting).ok();
                 self.audio_impl
                     .alternate_setting_changed(UsbDirection::Out, alt_setting);
+                // Start the IN cycle running
+                self.emit_feedback();
                 self.output.as_mut().unwrap().alt_setting = alt_setting;
                 xfer.accept().ok();
             }
@@ -1131,7 +1213,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
                     );
                 }
                 xfer.accept(|mut buf| {
-                    let rate = self.clock_impl.get_sample_rate();
+                    let rate = self.audio_impl.sample_rate();
 
                     debug!("    {}", rate);
                     buf.write_u32::<LittleEndian>(rate)
@@ -1148,7 +1230,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
                         channel
                     );
                 }
-                xfer.accept(|mut buf| match self.clock_impl.get_clock_validity() {
+                xfer.accept(|mut buf| match self.audio_impl.clock_validity() {
                     Ok(valid) => {
                         debug!("    {}", valid);
                         buf.write_u8(valid as u8)
@@ -1178,7 +1260,10 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
                 match xfer.data().read_u32::<LittleEndian>() {
                     Ok(rate) => {
                         debug!("   SET SamplingFreqControl CUR {}", rate);
-                        self.clock_impl.set_sample_rate(rate).ok();
+                        self.audio_impl.set_sample_rate(rate).ok();
+                        self.nominal_fb = UsbIsochronousFeedback::new_float(
+                            rate.to_f32().unwrap() / self.audio_rate.to_f32().unwrap(),
+                        );
                         xfer.accept().ok();
                     }
                     Err(e) => {
@@ -1201,7 +1286,7 @@ impl<'a, B: UsbBus, CS: UsbAudioClockImpl, AU: UsbAudioClass<'a, B>> AudioClass<
                         channel
                     );
                 }
-                xfer.accept(|mut buf| match self.clock_impl.get_rates() {
+                xfer.accept(|mut buf| match self.audio_impl.sample_rates() {
                     Ok(rates) => {
                         buf.write_u16::<LittleEndian>(rates.len() as u16)
                             .map_err(|_e| UsbError::BufferOverflow)?;