feature: modify i2s interface/implementation to better match specification

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/i2s.go

@@ -1,4 +1,4 @@
-//go:build sam
+//go:build sam && atsamd21
 
 // This is the definition for I2S bus functions.
 // Actual implementations if available for any given hardware
@@ -9,6 +9,22 @@
 
 package machine
 
+import "errors"
+
+// If you are getting a compile error on this line please check to see you've
+// correctly implemented the methods on the I2S type. They must match
+// the interface method signatures type to type perfectly.
+// If not implementing the I2S type please remove your target from the build tags
+// at the top of this file.
+var _ interface {
+	SetSampleFrequency(freq uint32) error
+	ReadMono(b []uint16) (int, error)
+	ReadStereo(b []uint32) (int, error)
+	WriteMono(b []uint16) (int, error)
+	WriteStereo(b []uint32) (int, error)
+	Enable(enabled bool)
+} = (*I2S)(nil)
+
 type I2SMode uint8
 type I2SStandard uint8
 type I2SClockSource uint8
@@ -18,6 +34,7 @@ const (
 	I2SModeSource I2SMode = iota
 	I2SModeReceiver
 	I2SModePDM
+	I2SModeSourceReceiver
 )
 
 const (
@@ -39,11 +56,20 @@ const (
 	I2SDataFormat32bit                 = 32
 )
 
+var (
+	ErrInvalidSampleFrequency = errors.New("i2s: invalid sample frequency")
+)
+
 // All fields are optional and may not be required or used on a particular platform.
 type I2SConfig struct {
-	SCK             Pin
-	WS              Pin
-	SD              Pin
+	// clock
+	SCK Pin
+	// word select
+	WS Pin
+	// data out
+	SDO Pin
+	// data in
+	SDI             Pin
 	Mode            I2SMode
 	Standard        I2SStandard
 	ClockSource     I2SClockSource