ak4490: add mute/unmute/proper volume implementation

firmware/src/dac/ak4490.rs

@@ -24,6 +24,7 @@ enum RegisterAddress {
 pub struct Ak4490Dac<T> {
     i2c: T,
     pins: CodecPins, // this dependency is unfortunate, but non trivial to generalize
+    volume: (u8, u8),
 }
 
 impl<T> Ak4490Dac<T>
@@ -43,6 +44,10 @@ where
             _ => 5,
         }
     }
+    fn set_volume_impl(&mut self, left: u8, right: u8) {
+        self.write_reg(RegisterAddress::LeftAtt, left);
+        self.write_reg(RegisterAddress::RightAtt, right);
+    }
 }
 
 impl<T> Dac<T> for Ak4490Dac<T>
@@ -50,7 +55,11 @@ where
     T: _embedded_hal_blocking_i2c_WriteRead + _embedded_hal_blocking_i2c_Write,
 {
     fn new(i2c: T, pins: CodecPins) -> Self {
-        Self { i2c, pins }
+        Self {
+            i2c,
+            pins,
+            volume: (0xff, 0xff),
+        }
     }
     fn init(&mut self) {
         // bring out of reset
@@ -66,7 +75,13 @@ where
         self.write_reg(RegisterAddress::Control4, (dfs & 0x4) >> 1);
     }
     fn set_volume(&mut self, left: u8, right: u8) {
-        self.write_reg(RegisterAddress::LeftAtt, left);
-        self.write_reg(RegisterAddress::RightAtt, right);
+        self.set_volume_impl(left, right);
+        self.volume = (left, right);
+    }
+    fn mute(&mut self) {
+        self.set_volume_impl(0, 0);
+    }
+    fn unmute(&mut self) {
+        self.set_volume_impl(self.volume.0, self.volume.1);
     }
 }