machine/esp32c3: implement USB_SERIAL for USBCDC communication

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

src/machine/machine_esp32c3.go

@@ -504,3 +504,95 @@ func (uart *UART) writeByte(b byte) error {
 }
 
 func (uart *UART) flush() {}
+
+type Serialer interface {
+	WriteByte(c byte) error
+	Write(data []byte) (n int, err error)
+	Configure(config UARTConfig) error
+	Buffered() int
+	ReadByte() (byte, error)
+	DTR() bool
+	RTS() bool
+}
+
+// USB Serial/JTAG Controller
+// See esp32-c3_technical_reference_manual_en.pdf
+// pg. 736
+type USB_DEVICE struct {
+	Bus *esp.USB_DEVICE_Type
+}
+
+var (
+	_USBCDC = &USB_DEVICE{
+		Bus: esp.USB_DEVICE,
+	}
+
+	USBCDC Serialer = _USBCDC
+)
+
+var (
+	errUSBWrongSize            = errors.New("USB: invalid write size")
+	errUSBCouldNotWriteAllData = errors.New("USB: could not write all data")
+	errUSBBufferEmpty          = errors.New("USB: read buffer empty")
+)
+
+func (usbdev *USB_DEVICE) Configure(config UARTConfig) error {
+	return nil
+}
+
+func (usbdev *USB_DEVICE) WriteByte(c byte) error {
+	if usbdev.Bus.GetEP1_CONF_SERIAL_IN_EP_DATA_FREE() == 0 {
+		return errUSBCouldNotWriteAllData
+	}
+
+	usbdev.Bus.SetEP1_RDWR_BYTE(uint32(c))
+	usbdev.flush()
+
+	return nil
+}
+
+func (usbdev *USB_DEVICE) Write(data []byte) (n int, err error) {
+	if len(data) == 0 || len(data) > 64 {
+		return 0, errUSBWrongSize
+	}
+
+	for i, c := range data {
+		if usbdev.Bus.GetEP1_CONF_SERIAL_IN_EP_DATA_FREE() == 0 {
+			if i > 0 {
+				usbdev.flush()
+			}
+
+			return i, errUSBCouldNotWriteAllData
+		}
+		usbdev.Bus.SetEP1_RDWR_BYTE(uint32(c))
+	}
+
+	usbdev.flush()
+	return len(data), nil
+}
+
+func (usbdev *USB_DEVICE) Buffered() int {
+	return int(usbdev.Bus.GetEP1_CONF_SERIAL_OUT_EP_DATA_AVAIL())
+}
+
+func (usbdev *USB_DEVICE) ReadByte() (byte, error) {
+	if usbdev.Bus.GetEP1_CONF_SERIAL_OUT_EP_DATA_AVAIL() != 0 {
+		return byte(usbdev.Bus.GetEP1_RDWR_BYTE()), nil
+	}
+
+	return 0, nil
+}
+
+func (usbdev *USB_DEVICE) DTR() bool {
+	return false
+}
+
+func (usbdev *USB_DEVICE) RTS() bool {
+	return false
+}
+
+func (usbdev *USB_DEVICE) flush() {
+	usbdev.Bus.SetEP1_CONF_WR_DONE(1)
+	for usbdev.Bus.GetEP1_CONF_SERIAL_IN_EP_DATA_FREE() == 0 {
+	}
+}

src/machine/usb.go

@@ -90,6 +90,7 @@ const cdcLineInfoSize = 7
 var (
 	ErrUSBReadTimeout  = errors.New("USB read timeout")
 	ErrUSBBytesRead    = errors.New("USB invalid number of bytes read")
+	ErrUSBBytesWritten = errors.New("USB invalid number of bytes written")
 )
 
 var (

src/runtime/runtime_esp32c3.go

@@ -5,6 +5,7 @@ package runtime
 import (
 	"device/esp"
 	"device/riscv"
+	"machine"
 	"runtime/volatile"
 	"unsafe"
 )
@@ -53,6 +54,10 @@ func main() {
 	// Configure interrupt handler
 	interruptInit()
 
+	// Initialize UART.
+	machine.USBCDC.Configure(machine.UARTConfig{})
+	machine.InitSerial()
+
 	// Initialize main system timer used for time.Now.
 	initTimer()
 

src/runtime/runtime_esp32xx.go

@@ -10,22 +10,6 @@ import (
 
 type timeUnit int64
 
-func putchar(c byte) {
-	machine.Serial.WriteByte(c)
-}
-
-func getchar() byte {
-	for machine.Serial.Buffered() == 0 {
-		Gosched()
-	}
-	v, _ := machine.Serial.ReadByte()
-	return v
-}
-
-func buffered() int {
-	return machine.Serial.Buffered()
-}
-
 // Initialize .bss: zero-initialized global variables.
 // The .data section has already been loaded by the ROM bootloader.
 func clearbss() {
@@ -84,3 +68,19 @@ func sleepTicks(d timeUnit) {
 func exit(code int) {
 	abort()
 }
+
+func putchar(c byte) {
+	machine.Serial.WriteByte(c)
+}
+
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}

targets/esp32c3.json

@@ -2,7 +2,7 @@
 	"inherits": ["riscv32"],
 	"features": "+32bit,+c,+m,-64bit,-a,-d,-e,-experimental-zawrs,-experimental-zca,-experimental-zcd,-experimental-zcf,-experimental-zihintntl,-experimental-ztso,-experimental-zvfh,-f,-h,-relax,-save-restore,-svinval,-svnapot,-svpbmt,-v,-xtheadvdot,-xventanacondops,-zba,-zbb,-zbc,-zbkb,-zbkc,-zbkx,-zbs,-zdinx,-zfh,-zfhmin,-zfinx,-zhinx,-zhinxmin,-zicbom,-zicbop,-zicboz,-zihintpause,-zk,-zkn,-zknd,-zkne,-zknh,-zkr,-zks,-zksed,-zksh,-zkt,-zmmul,-zve32f,-zve32x,-zve64d,-zve64f,-zve64x,-zvl1024b,-zvl128b,-zvl16384b,-zvl2048b,-zvl256b,-zvl32768b,-zvl32b,-zvl4096b,-zvl512b,-zvl64b,-zvl65536b,-zvl8192b",
 	"build-tags": ["esp32c3", "esp"],
-	"serial": "uart",
+	"serial": "usb",
 	"rtlib": "compiler-rt",
 	"libc": "picolibc",
 	"cflags": [