machine: fix usb truncation?

Remove the sendUSBPacket maxLen param because this greatly confused the compiler.
It also fixes a bug where the length provided to the hardware may not match the length of the packet.
sendUSBPacket now panics if the sent packet is too big.

I also fixed some of the string descriptor logic where we could create a packet without fully populating it.

RP2* systems might require some more work since they are implemented very differently?
I don't have any of those to test with yet, so maybe someone can deal with them in a seperate PR?

builder/sizes_test.go

@@ -44,7 +44,7 @@ func TestBinarySize(t *testing.T) {
 		// microcontrollers
 		{"hifive1b", "examples/echo", 3668, 280, 0, 2244},
 		{"microbit", "examples/serial", 2694, 342, 8, 2248},
-		{"wioterminal", "examples/pininterrupt", 7187, 1489, 116, 6888},
+		{"wioterminal", "examples/pininterrupt", 6833, 1491, 120, 6888},
 
 		// TODO: also check wasm. Right now this is difficult, because
 		// wasm binaries are run through wasm-opt and therefore the

src/machine/machine_atsamd21_usb.go

@@ -337,7 +337,7 @@ func handleUSBSetAddress(setup usb.Setup) bool {
 
 // SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
 func SendUSBInPacket(ep uint32, data []byte) bool {
-	sendUSBPacket(ep, data, 0)
+	sendUSBPacket(ep, data)
 
 	// clear transfer complete flag
 	setEPINTFLAG(ep, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
@@ -351,27 +351,28 @@ func SendUSBInPacket(ep uint32, data []byte) bool {
 // Prevent file size increases: https://github.com/tinygo-org/tinygo/pull/998
 //
 //go:noinline
-func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
-	l := uint16(len(data))
-	if 0 < maxsize && maxsize < l {
-		l = maxsize
+func sendUSBPacket(ep uint32, data []byte) {
+	// Select the corresponding buffer.
+	buffer := udd_ep_control_cache_buffer[:]
+	if ep != 0 {
+		buffer = udd_ep_in_cache_buffer[ep][:]
 	}
 
-	// Set endpoint address for sending data
-	if ep == 0 {
-		copy(udd_ep_control_cache_buffer[:], data[:l])
-		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_control_cache_buffer))))
-	} else {
-		copy(udd_ep_in_cache_buffer[ep][:], data[:l])
-		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))
-	}
+	// Copy the packet to the buffer.
+	copy(buffer[:len(data)], data)
+
+	// Select the corresponding endpoint descriptor.
+	endpoint := &usbEndpointDescriptors[ep].DeviceDescBank[1]
+
+	// Set the endpoint address.
+	endpoint.ADDR.Set(uint32(uintptr(unsafe.Pointer(unsafe.SliceData(buffer)))))
 
 	// clear multi-packet size which is total bytes already sent
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
+	endpoint.PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
 
 	// set byte count, which is total number of bytes to be sent
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.SetBits((uint32(l) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+	endpoint.PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+	endpoint.PCKSIZE.SetBits((uint32(len(data)) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 }
 
 func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {

src/machine/machine_atsamd51_usb.go

@@ -340,7 +340,7 @@ func handleUSBSetAddress(setup usb.Setup) bool {
 
 // SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
 func SendUSBInPacket(ep uint32, data []byte) bool {
-	sendUSBPacket(ep, data, 0)
+	sendUSBPacket(ep, data)
 
 	// clear transfer complete flag
 	setEPINTFLAG(ep, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
@@ -354,27 +354,28 @@ func SendUSBInPacket(ep uint32, data []byte) bool {
 // Prevent file size increases: https://github.com/tinygo-org/tinygo/pull/998
 //
 //go:noinline
-func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
-	l := uint16(len(data))
-	if 0 < maxsize && maxsize < l {
-		l = maxsize
+func sendUSBPacket(ep uint32, data []byte) {
+	// Select the corresponding buffer.
+	buffer := udd_ep_control_cache_buffer[:]
+	if ep != 0 {
+		buffer = udd_ep_in_cache_buffer[ep][:]
 	}
 
-	// Set endpoint address for sending data
-	if ep == 0 {
-		copy(udd_ep_control_cache_buffer[:], data[:l])
-		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_control_cache_buffer))))
-	} else {
-		copy(udd_ep_in_cache_buffer[ep][:], data[:l])
-		usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))
-	}
+	// Copy the packet to the buffer.
+	copy(buffer[:len(data)], data)
+
+	// Select the corresponding endpoint descriptor.
+	endpoint := &usbEndpointDescriptors[ep].DeviceDescBank[1]
+
+	// Set the endpoint address.
+	endpoint.ADDR.Set(uint32(uintptr(unsafe.Pointer(unsafe.SliceData(buffer)))))
 
 	// clear multi-packet size which is total bytes already sent
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
+	endpoint.PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
 
 	// set byte count, which is total number of bytes to be sent
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.SetBits((uint32(l) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+	endpoint.PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
+	endpoint.PCKSIZE.SetBits((uint32(len(data)) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 }
 
 func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {

src/machine/machine_nrf52840_usb.go

@@ -256,7 +256,7 @@ func initEndpoint(ep, config uint32) {
 
 // SendUSBInPacket sends a packet for USBHID (interrupt in / bulk in).
 func SendUSBInPacket(ep uint32, data []byte) bool {
-	sendUSBPacket(ep, data, 0)
+	sendUSBPacket(ep, data)
 
 	// clear transfer complete flag
 	nrf.USBD.INTENCLR.Set(nrf.USBD_INTENCLR_ENDEPOUT0 << 4)
@@ -267,33 +267,32 @@ func SendUSBInPacket(ep uint32, data []byte) bool {
 // Prevent file size increases: https://github.com/tinygo-org/tinygo/pull/998
 //
 //go:noinline
-func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
+func sendUSBPacket(ep uint32, data []byte) {
+	// Select the corresponding buffer.
 	count := len(data)
-	if 0 < int(maxsize) && int(maxsize) < count {
-		count = int(maxsize)
-	}
-
+	var buffer []byte
 	if ep == 0 {
-		copy(udd_ep_control_cache_buffer[:], data[:count])
+		buffer = udd_ep_control_cache_buffer[:]
 		if count > usb.EndpointPacketSize {
+			// The packet must be sent in chunks.
 			sendOnEP0DATADONE.offset = usb.EndpointPacketSize
-			sendOnEP0DATADONE.ptr = &udd_ep_control_cache_buffer[sendOnEP0DATADONE.offset]
+			sendOnEP0DATADONE.ptr = &udd_ep_control_cache_buffer[usb.EndpointPacketSize]
 			sendOnEP0DATADONE.count = count - usb.EndpointPacketSize
 			count = usb.EndpointPacketSize
 		}
-		sendViaEPIn(
-			ep,
-			&udd_ep_control_cache_buffer[0],
-			count,
-		)
 	} else {
-		copy(udd_ep_in_cache_buffer[ep][:], data[:count])
-		sendViaEPIn(
-			ep,
-			&udd_ep_in_cache_buffer[ep][0],
-			count,
-		)
+		buffer = udd_ep_in_cache_buffer[ep][:]
 	}
+
+	// Copy the packet to the buffer.
+	copy(buffer[:len(data)], data)
+
+	// Send the first chunk of the packet.
+	sendViaEPIn(
+		ep,
+		&buffer[0],
+		count,
+	)
 }
 
 func handleEndpointRx(ep uint32) []byte {

src/machine/machine_rp2040_usb.go

@@ -128,7 +128,7 @@ func handleUSBSetAddress(setup usb.Setup) bool {
 	const ackTimeout = 570
 
 	rp.USBCTRL_REGS.SIE_STATUS.Set(rp.USBCTRL_REGS_SIE_STATUS_ACK_REC)
-	sendUSBPacket(0, []byte{}, 0)
+	sendUSBPacket(0, []byte{})
 
 	// Wait for transfer to complete with a timeout.
 	t := timer.timeElapsed()

src/machine/machine_rp2350_usb.go

@@ -131,7 +131,7 @@ func handleUSBSetAddress(setup usb.Setup) bool {
 	const ackTimeout = 570
 
 	rp.USB.SIE_STATUS.Set(rp.USB_SIE_STATUS_ACK_REC)
-	sendUSBPacket(0, []byte{}, 0)
+	sendUSBPacket(0, []byte{})
 
 	// Wait for transfer to complete with a timeout.
 	t := timer.timeElapsed()

src/machine/machine_rp2_usb.go

@@ -72,19 +72,15 @@ func initEndpoint(ep, config uint32) {
 
 // SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
 func SendUSBInPacket(ep uint32, data []byte) bool {
-	sendUSBPacket(ep, data, 0)
+	sendUSBPacket(ep, data)
 	return true
 }
 
 // Prevent file size increases: https://github.com/tinygo-org/tinygo/pull/998
 //
 //go:noinline
-func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
+func sendUSBPacket(ep uint32, data []byte) {
 	count := len(data)
-	if 0 < int(maxsize) && int(maxsize) < count {
-		count = int(maxsize)
-	}
-
 	if ep == 0 {
 		if count > usb.EndpointPacketSize {
 			count = usb.EndpointPacketSize
@@ -145,7 +141,7 @@ func setEPDataPID(ep uint32, dataOne bool) {
 }
 
 func SendZlp() {
-	sendUSBPacket(0, []byte{}, 0)
+	sendUSBPacket(0, []byte{})
 }
 
 func sendViaEPIn(ep uint32, data []byte, count int) {

src/machine/usb.go

@@ -81,21 +81,6 @@ func usbSerial() string {
 	return ""
 }
 
-// strToUTF16LEDescriptor converts a utf8 string into a string descriptor
-// note: the following code only converts ascii characters to UTF16LE. In order
-// to do a "proper" conversion, we would need to pull in the 'unicode/utf16'
-// package, which at the time this was written added 512 bytes to the compiled
-// binary.
-func strToUTF16LEDescriptor(in string, out []byte) {
-	out[0] = byte(len(out))
-	out[1] = descriptor.TypeString
-	for i, rune := range in {
-		out[(i<<1)+2] = byte(rune)
-		out[(i<<1)+3] = 0
-	}
-	return
-}
-
 const cdcLineInfoSize = 7
 
 var (
@@ -137,51 +122,53 @@ var (
 	usbStallHandler [NumberOfUSBEndpoints]func(usb.Setup) bool
 )
 
+var usbLangInfo = [4]byte{
+	// length = 4 bytes
+	0x04,
+	// descriptor type = string
+	0x03,
+	// language codes
+	// 0x0409 = English (United States)
+	0x09, 0x04,
+}
+
 // sendDescriptor creates and sends the various USB descriptor types that
 // can be requested by the host.
 func sendDescriptor(setup usb.Setup) {
 	switch setup.WValueH {
 	case descriptor.TypeConfiguration:
-		sendUSBPacket(0, usbDescriptor.Configuration, setup.WLength)
+		sendDescriptorData(usbDescriptor.Configuration, setup.WLength)
 		return
+
 	case descriptor.TypeDevice:
 		usbDescriptor.Configure(usbVendorID(), usbProductID())
-		sendUSBPacket(0, usbDescriptor.Device, setup.WLength)
+		sendDescriptorData(usbDescriptor.Device, setup.WLength)
 		return
 
 	case descriptor.TypeString:
 		switch setup.WValueL {
 		case 0:
-			usb_trans_buffer[0] = 0x04
-			usb_trans_buffer[1] = 0x03
-			usb_trans_buffer[2] = 0x09
-			usb_trans_buffer[3] = 0x04
-			sendUSBPacket(0, usb_trans_buffer[:4], setup.WLength)
+			sendDescriptorData(usbLangInfo[:], setup.WLength)
 
 		case usb.IPRODUCT:
-			b := usb_trans_buffer[:(len(usbProduct())<<1)+2]
-			strToUTF16LEDescriptor(usbProduct(), b)
-			sendUSBPacket(0, b, setup.WLength)
+			sendDescriptorString(usbProduct(), setup.WLength)
 
 		case usb.IMANUFACTURER:
-			b := usb_trans_buffer[:(len(usbManufacturer())<<1)+2]
-			strToUTF16LEDescriptor(usbManufacturer(), b)
-			sendUSBPacket(0, b, setup.WLength)
+			sendDescriptorString(usbManufacturer(), setup.WLength)
 
 		case usb.ISERIAL:
-			sz := len(usbSerial())
-			if sz == 0 {
+			serial := usbSerial()
+			if len(serial) == 0 {
 				SendZlp()
 			} else {
-				b := usb_trans_buffer[:(sz<<1)+2]
-				strToUTF16LEDescriptor(usbSerial(), b)
-				sendUSBPacket(0, b, setup.WLength)
+				sendDescriptorString(serial, setup.WLength)
 			}
 		}
+		// TODO: why do we do this when WValueL is unknown?
 		return
 	case descriptor.TypeHIDReport:
 		if h, ok := usbDescriptor.HID[setup.WIndex]; ok {
-			sendUSBPacket(0, h, setup.WLength)
+			sendDescriptorData(h, setup.WLength)
 			return
 		}
 	case descriptor.TypeDeviceQualifier:
@@ -194,6 +181,39 @@ func sendDescriptor(setup usb.Setup) {
 	return
 }
 
+// sendDescriptorString sends a string descriptor, truncating it to fit maxLen or the buffer size.
+// note: the following code only converts ascii characters to UTF16LE. In order
+// to do a "proper" conversion, we would need to pull in the 'unicode/utf16'
+// package, which at the time this was written added 512 bytes to the compiled
+// binary.
+// TODO: old comment, re-evaluate
+func sendDescriptorString(data string, maxLen uint16) {
+	if maxLen < 2 {
+		// Something has gone horribly wrong.
+		SendZlp()
+		return
+	}
+
+	// Clamp the length.
+	maxEncBytes := min(len(usb_trans_buffer), len(udd_ep_control_cache_buffer), int(maxLen))
+	data = data[:min(len(data), (maxEncBytes-2)/2)]
+
+	// Write the header.
+	buf := usb_trans_buffer[:2*len(data)+2]
+	hdr, body := buf[:2], buf[2:]
+	hdr[0] = byte(len(buf))
+	hdr[1] = descriptor.TypeString
+
+	// Convert the string to UTF16.
+	// NOTE: Using range here would cause the length to disagree when multibyte codepoints are present.
+	for i := 0; i < len(data); i++ {
+		body[2*i] = byte(data[i])
+		body[2*i+1] = 0
+	}
+
+	sendUSBPacket(0, buf)
+}
+
 func handleStandardSetup(setup usb.Setup) bool {
 	switch setup.BRequest {
 	case usb.GET_STATUS:
@@ -206,7 +226,7 @@ func handleStandardSetup(setup usb.Setup) bool {
 			}
 		}
 
-		sendUSBPacket(0, usb_trans_buffer[:2], setup.WLength)
+		sendDescriptorData(usb_trans_buffer[:2], setup.WLength)
 		return true
 
 	case usb.CLEAR_FEATURE:
@@ -251,7 +271,7 @@ func handleStandardSetup(setup usb.Setup) bool {
 
 	case usb.GET_CONFIGURATION:
 		usb_trans_buffer[0] = usbConfiguration
-		sendUSBPacket(0, usb_trans_buffer[:1], setup.WLength)
+		sendDescriptorData(usb_trans_buffer[:1], setup.WLength)
 		return true
 
 	case usb.SET_CONFIGURATION:
@@ -271,7 +291,7 @@ func handleStandardSetup(setup usb.Setup) bool {
 
 	case usb.GET_INTERFACE:
 		usb_trans_buffer[0] = usbSetInterface
-		sendUSBPacket(0, usb_trans_buffer[:1], setup.WLength)
+		sendDescriptorData(usb_trans_buffer[:1], setup.WLength)
 		return true
 
 	case usb.SET_INTERFACE:
@@ -285,6 +305,21 @@ func handleStandardSetup(setup usb.Setup) bool {
 	}
 }
 
+// sendDescriptorData sends a descriptor, truncating it to fit maxLen or the buffer size.
+func sendDescriptorData(data []byte, maxLen uint16) {
+	data = lenToCap(data)
+	data = data[:min(len(data), len(udd_ep_control_cache_buffer), int(maxLen))]
+	sendUSBPacket(0, data)
+}
+
+// Set the cap of the slice to the length.
+// This is safe, but cannot be proven by the compiler.
+//
+//go:nobounds
+func lenToCap(b []byte) []byte {
+	return b[:len(b):len(b)]
+}
+
 func EnableCDC(txHandler func(), rxHandler func([]byte), setupHandler func(usb.Setup) bool) {
 	if len(usbDescriptor.Device) == 0 {
 		usbDescriptor = descriptor.CDC