samd21,samd51,nrf52840: move usbcdc to machine/usb/cdc (#2972)

* samd21,samd51,nrf52840: move usbcdc to machine/usb/cdc

15 files changed, 662 insertions, 839 deletions

diff --git a/src/machine/machine_atsamd21_usb.go b/src/machine/machine_atsamd21_usb.go
index d79a52d5c..1a920100e 100644
--- a/src/machine/machine_atsamd21_usb.go
+++ b/src/machine/machine_atsamd21_usb.go
@@ -1,141 +1,14 @@
 //go:build sam && atsamd21
 // +build sam,atsamd21
 
-// Peripheral abstraction layer for the atsamd21.
-//
-// Datasheet:
-// http://ww1.microchip.com/downloads/en/DeviceDoc/SAMD21-Family-DataSheet-DS40001882D.pdf
-//
 package machine
 
 import (
 	"device/sam"
 	"runtime/interrupt"
-	"runtime/volatile"
 	"unsafe"
 )
 
-// USBCDC is the USB CDC aka serial over USB interface on the SAMD21.
-type USBCDC struct {
-	Buffer            *RingBuffer
-	TxIdx             volatile.Register8
-	waitTxc           bool
-	waitTxcRetryCount uint8
-	sent              bool
-}
-
-var (
-	USB        = &USBCDC{Buffer: NewRingBuffer()}
-	waitHidTxc bool
-)
-
-const (
-	usbcdcTxSizeMask          uint8 = 0x3F
-	usbcdcTxBankMask          uint8 = ^usbcdcTxSizeMask
-	usbcdcTxBank1st           uint8 = 0x00
-	usbcdcTxBank2nd           uint8 = usbcdcTxSizeMask + 1
-	usbcdcTxMaxRetriesAllowed uint8 = 5
-)
-
-// Flush flushes buffered data.
-func (usbcdc *USBCDC) Flush() error {
-	if usbLineInfo.lineState > 0 {
-		idx := usbcdc.TxIdx.Get()
-		sz := idx & usbcdcTxSizeMask
-		bk := idx & usbcdcTxBankMask
-		if 0 < sz {
-
-			if usbcdc.waitTxc {
-				// waiting for the next flush(), because the transmission is not complete
-				usbcdc.waitTxcRetryCount++
-				return nil
-			}
-			usbcdc.waitTxc = true
-			usbcdc.waitTxcRetryCount = 0
-
-			// set the data
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][bk]))))
-			if bk == usbcdcTxBank1st {
-				usbcdc.TxIdx.Set(usbcdcTxBank2nd)
-			} else {
-				usbcdc.TxIdx.Set(usbcdcTxBank1st)
-			}
-
-			// clean multi packet size of bytes already sent
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
-
-			// set count of bytes to be sent
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.SetBits((uint32(sz) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-
-			// clear transfer complete flag
-			setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
-
-			// send data by setting bank ready
-			setEPSTATUSSET(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPSTATUSSET_BK1RDY)
-			usbcdc.sent = true
-		}
-	}
-	return nil
-}
-
-// WriteByte writes a byte of data to the USB CDC interface.
-func (usbcdc *USBCDC) WriteByte(c byte) error {
-	// Supposedly to handle problem with Windows USB serial ports?
-	if usbLineInfo.lineState > 0 {
-		ok := false
-		for {
-			mask := interrupt.Disable()
-
-			idx := usbcdc.TxIdx.Get()
-			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
-				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				usbcdc.TxIdx.Set(idx + 1)
-				ok = true
-			}
-
-			interrupt.Restore(mask)
-
-			if ok {
-				break
-			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
-				mask := interrupt.Disable()
-				usbcdc.waitTxc = false
-				usbcdc.waitTxcRetryCount = 0
-				usbcdc.TxIdx.Set(0)
-				usbLineInfo.lineState = 0
-				interrupt.Restore(mask)
-				break
-			} else {
-				mask := interrupt.Disable()
-				if usbcdc.sent {
-					if usbcdc.waitTxc {
-						if (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_EPINTFLAG_TRCPT1) != 0 {
-							setEPSTATUSCLR(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPSTATUSCLR_BK1RDY)
-							setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
-							usbcdc.waitTxc = false
-							usbcdc.Flush()
-						}
-					} else {
-						usbcdc.Flush()
-					}
-				}
-				interrupt.Restore(mask)
-			}
-		}
-	}
-
-	return nil
-}
-
-func (usbcdc *USBCDC) DTR() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
-}
-
-func (usbcdc *USBCDC) RTS() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
-}
-
 const (
 	// these are SAMD21 specific.
 	usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos  = 0
@@ -193,10 +66,6 @@ func (dev *USBDevice) Configure(config UARTConfig) {
 	dev.initcomplete = true
 }
 
-func (usbcdc *USBCDC) Configure(config UARTConfig) {
-	// dummy
-}
-
 func handlePadCalibration() {
 	// Load Pad Calibration data from non-volatile memory
 	// This requires registers that are not included in the SVD file.
@@ -258,11 +127,7 @@ func handleUSBIRQ(intr interrupt.Interrupt) {
 
 	// Start of frame
 	if (flags & sam.USB_DEVICE_INTFLAG_SOF) > 0 {
-		USB.Flush()
 		// if you want to blink LED showing traffic, this would be the place...
-		if hidCallback != nil && !waitHidTxc {
-			hidCallback()
-		}
 	}
 
 	// Endpoint 0 Setup interrupt
@@ -283,11 +148,8 @@ func handleUSBIRQ(intr interrupt.Interrupt) {
 			ok = handleStandardSetup(setup)
 		} else {
 			// Class Interface Requests
-			if setup.WIndex == usb_CDC_ACM_INTERFACE {
-				ok = cdcSetup(setup)
-			} else if setup.BmRequestType == usb_SET_REPORT_TYPE && setup.BRequest == usb_SET_IDLE {
-				SendZlp()
-				ok = true
+			if setup.WIndex < uint16(len(usbSetupHandler)) && usbSetupHandler[setup.WIndex] != nil {
+				ok = usbSetupHandler[setup.WIndex](setup)
 			}
 		}
 
@@ -313,22 +175,16 @@ func handleUSBIRQ(intr interrupt.Interrupt) {
 	for i = 1; i < uint32(len(endPoints)); i++ {
 		// Check if endpoint has a pending interrupt
 		epFlags := getEPINTFLAG(i)
-		if (epFlags&sam.USB_DEVICE_EPINTFLAG_TRCPT0) > 0 ||
-			(epFlags&sam.USB_DEVICE_EPINTFLAG_TRCPT1) > 0 {
-			switch i {
-			case usb_CDC_ENDPOINT_OUT:
-				handleEndpoint(i)
-				setEPINTFLAG(i, epFlags)
-			case usb_CDC_ENDPOINT_IN, usb_CDC_ENDPOINT_ACM:
-				setEPSTATUSCLR(i, sam.USB_DEVICE_EPSTATUSCLR_BK1RDY)
-				setEPINTFLAG(i, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
-
-				if i == usb_CDC_ENDPOINT_IN {
-					USB.waitTxc = false
-				}
-			case usb_HID_ENDPOINT_IN:
-				setEPINTFLAG(i, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
-				waitHidTxc = false
+		setEPINTFLAG(i, epFlags)
+		if (epFlags & sam.USB_DEVICE_EPINTFLAG_TRCPT0) > 0 {
+			buf := handleEndpointRx(i)
+			if usbRxHandler[i] != nil {
+				usbRxHandler[i](buf)
+			}
+			handleEndpointRxComplete(i)
+		} else if (epFlags & sam.USB_DEVICE_EPINTFLAG_TRCPT1) > 0 {
+			if usbTxHandler[i] != nil {
+				usbTxHandler[i]()
 			}
 		}
 	}
@@ -448,66 +304,8 @@ func handleUSBSetAddress(setup USBSetup) bool {
 	return true
 }
 
-func cdcSetup(setup USBSetup) bool {
-	if setup.BmRequestType == usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_GET_LINE_CODING {
-			var b [cdcLineInfoSize]byte
-			b[0] = byte(usbLineInfo.dwDTERate)
-			b[1] = byte(usbLineInfo.dwDTERate >> 8)
-			b[2] = byte(usbLineInfo.dwDTERate >> 16)
-			b[3] = byte(usbLineInfo.dwDTERate >> 24)
-			b[4] = byte(usbLineInfo.bCharFormat)
-			b[5] = byte(usbLineInfo.bParityType)
-			b[6] = byte(usbLineInfo.bDataBits)
-
-			sendUSBPacket(0, b[:], setup.WLength)
-			return true
-		}
-	}
-
-	if setup.BmRequestType == usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_SET_LINE_CODING {
-			b, err := receiveUSBControlPacket()
-			if err != nil {
-				return false
-			}
-
-			usbLineInfo.dwDTERate = uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
-			usbLineInfo.bCharFormat = b[4]
-			usbLineInfo.bParityType = b[5]
-			usbLineInfo.bDataBits = b[6]
-		}
-
-		if setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
-			usbLineInfo.lineState = setup.WValueL
-		}
-
-		if setup.BRequest == usb_CDC_SET_LINE_CODING || setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
-			// auto-reset into the bootloader
-			if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
-				EnterBootloader()
-			} else {
-				// TODO: cancel any reset
-			}
-			SendZlp()
-		}
-
-		if setup.BRequest == usb_CDC_SEND_BREAK {
-			// TODO: something with this value?
-			// breakValue = ((uint16_t)setup.wValueH << 8) | setup.wValueL;
-			// return false;
-			SendZlp()
-		}
-		return true
-	}
-	return false
-}
-
-// SendUSBHIDPacket sends a packet for USBHID (interrupt / in).
-func SendUSBHIDPacket(ep uint32, data []byte) bool {
-	if waitHidTxc {
-		return false
-	}
+// SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
+func SendUSBInPacket(ep uint32, data []byte) bool {
 	sendUSBPacket(ep, data, 0)
 
 	// clear transfer complete flag
@@ -516,8 +314,6 @@ func SendUSBHIDPacket(ep uint32, data []byte) bool {
 	// send data by setting bank ready
 	setEPSTATUSSET(ep, sam.USB_DEVICE_EPSTATUSSET_BK1RDY)
 
-	waitHidTxc = true
-
 	return true
 }
 
@@ -527,10 +323,15 @@ func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
 	if 0 < maxsize && maxsize < l {
 		l = maxsize
 	}
-	copy(udd_ep_in_cache_buffer[ep][:], data[:l])
 
 	// Set endpoint address for sending data
-	usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))
+	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]))))
+	}
 
 	// 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)
@@ -540,7 +341,7 @@ func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
 	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.SetBits((uint32(l) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 }
 
-func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
+func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	var b [cdcLineInfoSize]byte
 
 	// address
@@ -557,7 +358,7 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	for (getEPSTATUS(0) & sam.USB_DEVICE_EPSTATUS_BK0RDY) == 0 {
 		timeout--
 		if timeout == 0 {
-			return b, errUSBCDCReadTimeout
+			return b, ErrUSBReadTimeout
 		}
 	}
 
@@ -566,7 +367,7 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	for (getEPINTFLAG(0) & sam.USB_DEVICE_EPINTFLAG_TRCPT0) == 0 {
 		timeout--
 		if timeout == 0 {
-			return b, errUSBCDCReadTimeout
+			return b, ErrUSBReadTimeout
 		}
 	}
 
@@ -575,7 +376,7 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 		usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask)
 
 	if bytesread != cdcLineInfoSize {
-		return b, errUSBCDCBytesRead
+		return b, ErrUSBBytesRead
 	}
 
 	copy(b[:7], udd_ep_out_cache_buffer[0][:7])
@@ -583,16 +384,15 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	return b, nil
 }
 
-func handleEndpoint(ep uint32) {
+func handleEndpointRx(ep uint32) []byte {
 	// get data
 	count := int((usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.Get() >>
 		usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask)
 
-	// move to ring buffer
-	for i := 0; i < count; i++ {
-		USB.Receive(byte((udd_ep_out_cache_buffer[ep][i] & 0xFF)))
-	}
+	return udd_ep_out_cache_buffer[ep][:count]
+}
 
+func handleEndpointRxComplete(ep uint32) {
 	// set byte count to zero
 	usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 
@@ -601,6 +401,7 @@ func handleEndpoint(ep uint32) {
 
 	// set ready for next data
 	setEPSTATUSCLR(ep, sam.USB_DEVICE_EPSTATUSCLR_BK0RDY)
+
 }
 
 func SendZlp() {
diff --git a/src/machine/machine_atsamd51_usb.go b/src/machine/machine_atsamd51_usb.go
index a7d9e8910..2788fd0fd 100644
--- a/src/machine/machine_atsamd51_usb.go
+++ b/src/machine/machine_atsamd51_usb.go
@@ -1,142 +1,14 @@
 //go:build (sam && atsamd51) || (sam && atsame5x)
 // +build sam,atsamd51 sam,atsame5x
 
-// Peripheral abstraction layer for the atsamd51.
-//
-// Datasheet:
-// http://ww1.microchip.com/downloads/en/DeviceDoc/60001507C.pdf
-//
 package machine
 
 import (
 	"device/sam"
 	"runtime/interrupt"
-	"runtime/volatile"
 	"unsafe"
 )
 
-// USBCDC is the USB CDC aka serial over USB interface on the SAMD21.
-type USBCDC struct {
-	Buffer            *RingBuffer
-	TxIdx             volatile.Register8
-	waitTxc           bool
-	waitTxcRetryCount uint8
-	sent              bool
-}
-
-var (
-	// USB is a USB CDC interface.
-	USB        = &USBCDC{Buffer: NewRingBuffer()}
-	waitHidTxc bool
-)
-
-const (
-	usbcdcTxSizeMask          uint8 = 0x3F
-	usbcdcTxBankMask          uint8 = ^usbcdcTxSizeMask
-	usbcdcTxBank1st           uint8 = 0x00
-	usbcdcTxBank2nd           uint8 = usbcdcTxSizeMask + 1
-	usbcdcTxMaxRetriesAllowed uint8 = 5
-)
-
-// Flush flushes buffered data.
-func (usbcdc *USBCDC) Flush() error {
-	if usbLineInfo.lineState > 0 {
-		idx := usbcdc.TxIdx.Get()
-		sz := idx & usbcdcTxSizeMask
-		bk := idx & usbcdcTxBankMask
-		if 0 < sz {
-
-			if usbcdc.waitTxc {
-				// waiting for the next flush(), because the transmission is not complete
-				usbcdc.waitTxcRetryCount++
-				return nil
-			}
-			usbcdc.waitTxc = true
-			usbcdc.waitTxcRetryCount = 0
-
-			// set the data
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][bk]))))
-			if bk == usbcdcTxBank1st {
-				usbcdc.TxIdx.Set(usbcdcTxBank2nd)
-			} else {
-				usbcdc.TxIdx.Set(usbcdcTxBank1st)
-			}
-
-			// clean multi packet size of bytes already sent
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Mask << usb_DEVICE_PCKSIZE_MULTI_PACKET_SIZE_Pos)
-
-			// set count of bytes to be sent
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-			usbEndpointDescriptors[usb_CDC_ENDPOINT_IN].DeviceDescBank[1].PCKSIZE.SetBits((uint32(sz) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
-
-			// clear transfer complete flag
-			setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
-
-			// send data by setting bank ready
-			setEPSTATUSSET(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPSTATUSSET_BK1RDY)
-			usbcdc.sent = true
-		}
-	}
-	return nil
-}
-
-// WriteByte writes a byte of data to the USB CDC interface.
-func (usbcdc *USBCDC) WriteByte(c byte) error {
-	// Supposedly to handle problem with Windows USB serial ports?
-	if usbLineInfo.lineState > 0 {
-		ok := false
-		for {
-			mask := interrupt.Disable()
-
-			idx := usbcdc.TxIdx.Get()
-			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
-				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				usbcdc.TxIdx.Set(idx + 1)
-				ok = true
-			}
-
-			interrupt.Restore(mask)
-
-			if ok {
-				break
-			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
-				mask := interrupt.Disable()
-				usbcdc.waitTxc = false
-				usbcdc.waitTxcRetryCount = 0
-				usbcdc.TxIdx.Set(0)
-				usbLineInfo.lineState = 0
-				interrupt.Restore(mask)
-				break
-			} else {
-				mask := interrupt.Disable()
-				if usbcdc.sent {
-					if usbcdc.waitTxc {
-						if (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) != 0 {
-							setEPSTATUSCLR(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPSTATUSCLR_BK1RDY)
-							setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
-							usbcdc.waitTxc = false
-							usbcdc.Flush()
-						}
-					} else {
-						usbcdc.Flush()
-					}
-				}
-				interrupt.Restore(mask)
-			}
-		}
-	}
-
-	return nil
-}
-
-func (usbcdc *USBCDC) DTR() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
-}
-
-func (usbcdc *USBCDC) RTS() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
-}
-
 const (
 	// these are SAMD51 specific.
 	usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos  = 0
@@ -188,7 +60,7 @@ func (dev *USBDevice) Configure(config UARTConfig) {
 	// enable USB
 	sam.USB_DEVICE.CTRLA.SetBits(sam.USB_DEVICE_CTRLA_ENABLE)
 
-	// enable IRQ at highest priority
+	// enable IRQ
 	interrupt.New(sam.IRQ_USB_OTHER, handleUSBIRQ).Enable()
 	interrupt.New(sam.IRQ_USB_SOF_HSOF, handleUSBIRQ).Enable()
 	interrupt.New(sam.IRQ_USB_TRCPT0, handleUSBIRQ).Enable()
@@ -197,10 +69,6 @@ func (dev *USBDevice) Configure(config UARTConfig) {
 	dev.initcomplete = true
 }
 
-func (usbcdc *USBCDC) Configure(config UARTConfig) {
-	// dummy
-}
-
 func handlePadCalibration() {
 	// Load Pad Calibration data from non-volatile memory
 	// This requires registers that are not included in the SVD file.
@@ -244,7 +112,7 @@ func handlePadCalibration() {
 	sam.USB_DEVICE.PADCAL.SetBits(calibTrim << sam.USB_DEVICE_PADCAL_TRIM_Pos)
 }
 
-func handleUSBIRQ(interrupt.Interrupt) {
+func handleUSBIRQ(intr interrupt.Interrupt) {
 	// reset all interrupt flags
 	flags := sam.USB_DEVICE.INTFLAG.Get()
 	sam.USB_DEVICE.INTFLAG.Set(flags)
@@ -262,10 +130,6 @@ func handleUSBIRQ(interrupt.Interrupt) {
 
 	// Start of frame
 	if (flags & sam.USB_DEVICE_INTFLAG_SOF) > 0 {
-		USB.Flush()
-		if hidCallback != nil && !waitHidTxc {
-			hidCallback()
-		}
 		// if you want to blink LED showing traffic, this would be the place...
 	}
 
@@ -287,11 +151,8 @@ func handleUSBIRQ(interrupt.Interrupt) {
 			ok = handleStandardSetup(setup)
 		} else {
 			// Class Interface Requests
-			if setup.WIndex == usb_CDC_ACM_INTERFACE {
-				ok = cdcSetup(setup)
-			} else if setup.BmRequestType == usb_SET_REPORT_TYPE && setup.BRequest == usb_SET_IDLE {
-				SendZlp()
-				ok = true
+			if setup.WIndex < uint16(len(usbSetupHandler)) && usbSetupHandler[setup.WIndex] != nil {
+				ok = usbSetupHandler[setup.WIndex](setup)
 			}
 		}
 
@@ -317,22 +178,16 @@ func handleUSBIRQ(interrupt.Interrupt) {
 	for i = 1; i < uint32(len(endPoints)); i++ {
 		// Check if endpoint has a pending interrupt
 		epFlags := getEPINTFLAG(i)
-		if (epFlags&sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT0) > 0 ||
-			(epFlags&sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) > 0 {
-			switch i {
-			case usb_CDC_ENDPOINT_OUT:
-				handleEndpoint(i)
-				setEPINTFLAG(i, epFlags)
-			case usb_CDC_ENDPOINT_IN, usb_CDC_ENDPOINT_ACM:
-				setEPSTATUSCLR(i, sam.USB_DEVICE_ENDPOINT_EPSTATUSCLR_BK1RDY)
-				setEPINTFLAG(i, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
-
-				if i == usb_CDC_ENDPOINT_IN {
-					USB.waitTxc = false
-				}
-			case usb_HID_ENDPOINT_IN:
-				setEPINTFLAG(i, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
-				waitHidTxc = false
+		setEPINTFLAG(i, epFlags)
+		if (epFlags & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT0) > 0 {
+			buf := handleEndpointRx(i)
+			if usbRxHandler[i] != nil {
+				usbRxHandler[i](buf)
+			}
+			handleEndpointRxComplete(i)
+		} else if (epFlags & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) > 0 {
+			if usbTxHandler[i] != nil {
+				usbTxHandler[i]()
 			}
 		}
 	}
@@ -452,67 +307,8 @@ func handleUSBSetAddress(setup USBSetup) bool {
 	return true
 }
 
-func cdcSetup(setup USBSetup) bool {
-	if setup.BmRequestType == usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_GET_LINE_CODING {
-			var b [cdcLineInfoSize]byte
-			b[0] = byte(usbLineInfo.dwDTERate)
-			b[1] = byte(usbLineInfo.dwDTERate >> 8)
-			b[2] = byte(usbLineInfo.dwDTERate >> 16)
-			b[3] = byte(usbLineInfo.dwDTERate >> 24)
-			b[4] = byte(usbLineInfo.bCharFormat)
-			b[5] = byte(usbLineInfo.bParityType)
-			b[6] = byte(usbLineInfo.bDataBits)
-
-			sendUSBPacket(0, b[:], setup.WLength)
-			return true
-		}
-	}
-
-	if setup.BmRequestType == usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_SET_LINE_CODING {
-			b, err := receiveUSBControlPacket()
-			if err != nil {
-				return false
-			}
-
-			usbLineInfo.dwDTERate = uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
-			usbLineInfo.bCharFormat = b[4]
-			usbLineInfo.bParityType = b[5]
-			usbLineInfo.bDataBits = b[6]
-		}
-
-		if setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
-			usbLineInfo.lineState = setup.WValueL
-		}
-
-		if setup.BRequest == usb_CDC_SET_LINE_CODING || setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
-			// auto-reset into the bootloader
-			if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
-				EnterBootloader()
-			} else {
-				// TODO: cancel any reset
-			}
-			SendZlp()
-		}
-
-		if setup.BRequest == usb_CDC_SEND_BREAK {
-			// TODO: something with this value?
-			// breakValue = ((uint16_t)setup.wValueH << 8) | setup.wValueL;
-			// return false;
-			SendZlp()
-		}
-		return true
-	}
-	return false
-}
-
-// SendUSBHIDPacket sends a packet for USBHID (interrupt / in).
-func SendUSBHIDPacket(ep uint32, data []byte) bool {
-	if waitHidTxc {
-		return false
-	}
-
+// SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
+func SendUSBInPacket(ep uint32, data []byte) bool {
 	sendUSBPacket(ep, data, 0)
 
 	// clear transfer complete flag
@@ -521,8 +317,6 @@ func SendUSBHIDPacket(ep uint32, data []byte) bool {
 	// send data by setting bank ready
 	setEPSTATUSSET(ep, sam.USB_DEVICE_ENDPOINT_EPSTATUSSET_BK1RDY)
 
-	waitHidTxc = true
-
 	return true
 }
 
@@ -532,10 +326,15 @@ func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
 	if 0 < maxsize && maxsize < l {
 		l = maxsize
 	}
-	copy(udd_ep_in_cache_buffer[ep][:], data[:l])
 
 	// Set endpoint address for sending data
-	usbEndpointDescriptors[ep].DeviceDescBank[1].ADDR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_in_cache_buffer[ep]))))
+	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]))))
+	}
 
 	// 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)
@@ -545,7 +344,7 @@ func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
 	usbEndpointDescriptors[ep].DeviceDescBank[1].PCKSIZE.SetBits((uint32(l) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask) << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 }
 
-func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
+func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	var b [cdcLineInfoSize]byte
 
 	// address
@@ -562,16 +361,16 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	for (getEPSTATUS(0) & sam.USB_DEVICE_ENDPOINT_EPSTATUS_BK0RDY) == 0 {
 		timeout--
 		if timeout == 0 {
-			return b, errUSBCDCReadTimeout
+			return b, ErrUSBReadTimeout
 		}
 	}
 
 	// Wait until OUT transfer is completed.
 	timeout = 300000
-	for (getEPINTFLAG(0) & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) == 0 {
+	for (getEPINTFLAG(0) & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT0) == 0 {
 		timeout--
 		if timeout == 0 {
-			return b, errUSBCDCReadTimeout
+			return b, ErrUSBReadTimeout
 		}
 	}
 
@@ -580,7 +379,7 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 		usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask)
 
 	if bytesread != cdcLineInfoSize {
-		return b, errUSBCDCBytesRead
+		return b, ErrUSBBytesRead
 	}
 
 	copy(b[:7], udd_ep_out_cache_buffer[0][:7])
@@ -588,16 +387,15 @@ func receiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
 	return b, nil
 }
 
-func handleEndpoint(ep uint32) {
+func handleEndpointRx(ep uint32) []byte {
 	// get data
 	count := int((usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.Get() >>
 		usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos) & usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask)
 
-	// move to ring buffer
-	for i := 0; i < count; i++ {
-		USB.Receive(byte((udd_ep_out_cache_buffer[ep][i] & 0xFF)))
-	}
+	return udd_ep_out_cache_buffer[ep][:count]
+}
 
+func handleEndpointRxComplete(ep uint32) {
 	// set byte count to zero
 	usbEndpointDescriptors[ep].DeviceDescBank[0].PCKSIZE.ClearBits(usb_DEVICE_PCKSIZE_BYTE_COUNT_Mask << usb_DEVICE_PCKSIZE_BYTE_COUNT_Pos)
 
diff --git a/src/machine/machine_nrf52840_usb.go b/src/machine/machine_nrf52840_usb.go
index 2193e1430..28378fb48 100644
--- a/src/machine/machine_nrf52840_usb.go
+++ b/src/machine/machine_nrf52840_usb.go
@@ -11,127 +11,15 @@ import (
 	"unsafe"
 )
 
-// USBCDC is the USB CDC aka serial over USB interface on the nRF52840
-type USBCDC struct {
-	Buffer            *RingBuffer
-	TxIdx             volatile.Register8
-	waitTxc           bool
-	waitTxcRetryCount uint8
-	sent              bool
-}
-
-const (
-	usbcdcTxSizeMask          uint8 = 0x3F
-	usbcdcTxBankMask          uint8 = ^usbcdcTxSizeMask
-	usbcdcTxBank1st           uint8 = 0x00
-	usbcdcTxBank2nd           uint8 = usbcdcTxSizeMask + 1
-	usbcdcTxMaxRetriesAllowed uint8 = 5
-)
-
-// Flush flushes buffered data.
-func (usbcdc *USBCDC) Flush() error {
-	if usbLineInfo.lineState > 0 {
-		idx := usbcdc.TxIdx.Get()
-		sz := idx & usbcdcTxSizeMask
-		bk := idx & usbcdcTxBankMask
-		if 0 < sz {
-
-			if usbcdc.waitTxc {
-				// waiting for the next flush(), because the transmission is not complete
-				usbcdc.waitTxcRetryCount++
-				return nil
-			}
-			usbcdc.waitTxc = true
-			usbcdc.waitTxcRetryCount = 0
-
-			// set the data
-			enterCriticalSection()
-			sendViaEPIn(
-				usb_CDC_ENDPOINT_IN,
-				&udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][bk],
-				int(sz),
-			)
-			if bk == usbcdcTxBank1st {
-				usbcdc.TxIdx.Set(usbcdcTxBank2nd)
-			} else {
-				usbcdc.TxIdx.Set(usbcdcTxBank1st)
-			}
-
-			usbcdc.sent = true
-		}
-	}
-	return nil
-}
-
-// WriteByte writes a byte of data to the USB CDC interface.
-func (usbcdc *USBCDC) WriteByte(c byte) error {
-	// Supposedly to handle problem with Windows USB serial ports?
-	if usbLineInfo.lineState > 0 {
-		ok := false
-		for {
-			mask := interrupt.Disable()
-
-			idx := usbcdc.TxIdx.Get()
-			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
-				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				usbcdc.TxIdx.Set(idx + 1)
-				ok = true
-			}
-
-			interrupt.Restore(mask)
-
-			if ok {
-				break
-			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
-				mask := interrupt.Disable()
-				usbcdc.waitTxc = false
-				usbcdc.waitTxcRetryCount = 0
-				usbcdc.TxIdx.Set(0)
-				usbLineInfo.lineState = 0
-				interrupt.Restore(mask)
-				break
-			} else {
-				mask := interrupt.Disable()
-				if usbcdc.sent {
-					if usbcdc.waitTxc {
-						if !easyDMABusy.HasBits(1) {
-							usbcdc.waitTxc = false
-							usbcdc.Flush()
-						}
-					} else {
-						usbcdc.Flush()
-					}
-				}
-				interrupt.Restore(mask)
-			}
-		}
-	}
-
-	return nil
-}
-
-func (usbcdc *USBCDC) DTR() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
-}
-
-func (usbcdc *USBCDC) RTS() bool {
-	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
-}
-
 var (
-	USB        = &_USB
-	_USB       = USBCDC{Buffer: NewRingBuffer()}
-	waitHidTxc bool
-
 	sendOnEP0DATADONE struct {
-		ptr   *byte
-		count int
+		ptr    *byte
+		count  int
+		offset int
 	}
-
-	epinen                   uint32
-	epouten                  uint32
-	easyDMABusy              volatile.Register8
-	epout0data_setlinecoding bool
+	epinen      uint32
+	epouten     uint32
+	easyDMABusy volatile.Register8
 )
 
 // enterCriticalSection is used to protect access to easyDMA - only one thing
@@ -171,7 +59,7 @@ func (dev *USBDevice) Configure(config UARTConfig) {
 	intr.Enable()
 
 	// enable interrupt for end of reset and start of frame
-	nrf.USBD.INTEN.Set(nrf.USBD_INTENSET_USBEVENT | nrf.USBD_INTENSET_SOF)
+	nrf.USBD.INTEN.Set(nrf.USBD_INTENSET_USBEVENT)
 
 	// errata 187
 	// https://infocenter.nordicsemi.com/topic/errata_nRF52840_EngB/ERR/nRF52840/EngineeringB/latest/anomaly_840_187.html
@@ -199,17 +87,10 @@ func (dev *USBDevice) Configure(config UARTConfig) {
 	dev.initcomplete = true
 }
 
-func (usbcdc *USBCDC) Configure(config UARTConfig) {
-	// dummy
-}
-
 func handleUSBIRQ(interrupt.Interrupt) {
 	if nrf.USBD.EVENTS_SOF.Get() == 1 {
 		nrf.USBD.EVENTS_SOF.Set(0)
-		USB.Flush()
-		if hidCallback != nil && !waitHidTxc {
-			hidCallback()
-		}
+
 		// if you want to blink LED showing traffic, this would be the place...
 	}
 
@@ -230,22 +111,27 @@ func handleUSBIRQ(interrupt.Interrupt) {
 	if nrf.USBD.EVENTS_EP0DATADONE.Get() == 1 {
 		// done sending packet - either need to send another or enter status stage
 		nrf.USBD.EVENTS_EP0DATADONE.Set(0)
-		if epout0data_setlinecoding {
-			nrf.USBD.EPOUT[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_out_cache_buffer[0]))))
-			nrf.USBD.EPOUT[0].MAXCNT.Set(64)
-			nrf.USBD.TASKS_STARTEPOUT[0].Set(1)
-			return
-		}
 		if sendOnEP0DATADONE.ptr != nil {
 			// previous data was too big for one packet, so send a second
+			ptr := sendOnEP0DATADONE.ptr
+			count := sendOnEP0DATADONE.count
+			if count > usbEndpointPacketSize {
+				sendOnEP0DATADONE.offset += usbEndpointPacketSize
+				sendOnEP0DATADONE.ptr = &udd_ep_control_cache_buffer[sendOnEP0DATADONE.offset]
+				count = usbEndpointPacketSize
+			}
+			sendOnEP0DATADONE.count -= count
 			sendViaEPIn(
 				0,
-				sendOnEP0DATADONE.ptr,
-				sendOnEP0DATADONE.count,
+				ptr,
+				count,
 			)
 
 			// clear, so we know we're done
-			sendOnEP0DATADONE.ptr = nil
+			if sendOnEP0DATADONE.count == 0 {
+				sendOnEP0DATADONE.ptr = nil
+				sendOnEP0DATADONE.offset = 0
+			}
 		} else {
 			// no more data, so set status stage
 			SendZlp() // nrf.USBD.TASKS_EP0STATUS.Set(1)
@@ -266,11 +152,9 @@ func handleUSBIRQ(interrupt.Interrupt) {
 			// Standard Requests
 			ok = handleStandardSetup(setup)
 		} else {
-			if setup.WIndex == usb_CDC_ACM_INTERFACE {
-				ok = cdcSetup(setup)
-			} else if setup.BmRequestType == usb_SET_REPORT_TYPE && setup.BRequest == usb_SET_IDLE {
-				SendZlp()
-				ok = true
+			// Class Interface Requests
+			if setup.WIndex < uint16(len(usbSetupHandler)) && usbSetupHandler[setup.WIndex] != nil {
+				ok = usbSetupHandler[setup.WIndex](setup)
 			}
 		}
 
@@ -290,25 +174,16 @@ func handleUSBIRQ(interrupt.Interrupt) {
 			// Check if endpoint has a pending interrupt
 			inDataDone := epDataStatus&(nrf.USBD_EPDATASTATUS_EPIN1<<(i-1)) > 0
 			outDataDone := epDataStatus&(nrf.USBD_EPDATASTATUS_EPOUT1<<(i-1)) > 0
-			if inDataDone || outDataDone {
-				switch i {
-				case usb_CDC_ENDPOINT_OUT:
-					// setup buffer to receive from host
-					if outDataDone {
-						enterCriticalSection()
-						nrf.USBD.EPOUT[i].PTR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_out_cache_buffer[i]))))
-						count := nrf.USBD.SIZE.EPOUT[i].Get()
-						nrf.USBD.EPOUT[i].MAXCNT.Set(count)
-						nrf.USBD.TASKS_STARTEPOUT[i].Set(1)
-					}
-				case usb_CDC_ENDPOINT_IN: //, usb_CDC_ENDPOINT_ACM:
-					if inDataDone {
-						USB.waitTxc = false
-						exitCriticalSection()
-					}
-				case usb_HID_ENDPOINT_IN:
-					waitHidTxc = false
+			if inDataDone {
+				if usbTxHandler[i] != nil {
+					usbTxHandler[i]()
 				}
+			} else if outDataDone {
+				enterCriticalSection()
+				nrf.USBD.EPOUT[i].PTR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_out_cache_buffer[i]))))
+				count := nrf.USBD.SIZE.EPOUT[i].Get()
+				nrf.USBD.EPOUT[i].MAXCNT.Set(count)
+				nrf.USBD.TASKS_STARTEPOUT[i].Set(1)
 			}
 		}
 	}
@@ -317,32 +192,16 @@ func handleUSBIRQ(interrupt.Interrupt) {
 	for i := 0; i < len(endPoints); i++ {
 		if nrf.USBD.EVENTS_ENDEPOUT[i].Get() > 0 {
 			nrf.USBD.EVENTS_ENDEPOUT[i].Set(0)
-			if i == 0 && epout0data_setlinecoding {
-				epout0data_setlinecoding = false
-				count := int(nrf.USBD.SIZE.EPOUT[0].Get())
-				if count >= 7 {
-					parseUSBLineInfo(udd_ep_out_cache_buffer[0][:count])
-					if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
-						EnterBootloader()
-					}
-				}
-				nrf.USBD.TASKS_EP0STATUS.Set(1)
-			}
-			if i == usb_CDC_ENDPOINT_OUT {
-				USB.handleEndpoint(uint32(i))
+			buf := handleEndpointRx(uint32(i))
+			if usbRxHandler[i] != nil {
+				usbRxHandler[i](buf)
 			}
+			handleEndpointRxComplete(uint32(i))
 			exitCriticalSection()
 		}
 	}
 }
 
-func parseUSBLineInfo(b []byte) {
-	usbLineInfo.dwDTERate = uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
-	usbLineInfo.bCharFormat = b[4]
-	usbLineInfo.bParityType = b[5]
-	usbLineInfo.bDataBits = b[6]
-}
-
 func parseUSBSetupRegisters() USBSetup {
 	return USBSetup{
 		BmRequestType: uint8(nrf.USBD.BMREQUESTTYPE.Get()),
@@ -383,59 +242,13 @@ func initEndpoint(ep, config uint32) {
 	}
 }
 
-func cdcSetup(setup USBSetup) bool {
-	if setup.BmRequestType == usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_GET_LINE_CODING {
-			var b [cdcLineInfoSize]byte
-			b[0] = byte(usbLineInfo.dwDTERate)
-			b[1] = byte(usbLineInfo.dwDTERate >> 8)
-			b[2] = byte(usbLineInfo.dwDTERate >> 16)
-			b[3] = byte(usbLineInfo.dwDTERate >> 24)
-			b[4] = byte(usbLineInfo.bCharFormat)
-			b[5] = byte(usbLineInfo.bParityType)
-			b[6] = byte(usbLineInfo.bDataBits)
-
-			sendUSBPacket(0, b[:], setup.WLength)
-			return true
-		}
-	}
-
-	if setup.BmRequestType == usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE {
-		if setup.BRequest == usb_CDC_SET_LINE_CODING {
-			epout0data_setlinecoding = true
-			nrf.USBD.TASKS_EP0RCVOUT.Set(1)
-			return true
-		}
-
-		if setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
-			usbLineInfo.lineState = setup.WValueL
-			if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
-				EnterBootloader()
-			}
-			nrf.USBD.TASKS_EP0STATUS.Set(1)
-		}
-
-		if setup.BRequest == usb_CDC_SEND_BREAK {
-			nrf.USBD.TASKS_EP0STATUS.Set(1)
-		}
-		return true
-	}
-	return false
-}
-
-// SendUSBHIDPacket sends a packet for USBHID (interrupt / in).
-func SendUSBHIDPacket(ep uint32, data []byte) bool {
-	if waitHidTxc {
-		return false
-	}
-
+// SendUSBInPacket sends a packet for USBHID (interrupt in / bulk in).
+func SendUSBInPacket(ep uint32, data []byte) bool {
 	sendUSBPacket(ep, data, 0)
 
 	// clear transfer complete flag
 	nrf.USBD.INTENCLR.Set(nrf.USBD_INTENCLR_ENDEPOUT0 << 4)
 
-	waitHidTxc = true
-
 	return true
 }
 
@@ -445,28 +258,38 @@ func sendUSBPacket(ep uint32, data []byte, maxsize uint16) {
 	if 0 < int(maxsize) && int(maxsize) < count {
 		count = int(maxsize)
 	}
-	copy(udd_ep_in_cache_buffer[ep][:], data[:count])
-	if ep == 0 && count > usbEndpointPacketSize {
-		sendOnEP0DATADONE.ptr = &udd_ep_in_cache_buffer[ep][usbEndpointPacketSize]
-		sendOnEP0DATADONE.count = count - usbEndpointPacketSize
-		count = usbEndpointPacketSize
+
+	if ep == 0 {
+		copy(udd_ep_control_cache_buffer[:], data[:count])
+		if count > usbEndpointPacketSize {
+			sendOnEP0DATADONE.offset = usbEndpointPacketSize
+			sendOnEP0DATADONE.ptr = &udd_ep_control_cache_buffer[sendOnEP0DATADONE.offset]
+			sendOnEP0DATADONE.count = count - usbEndpointPacketSize
+			count = usbEndpointPacketSize
+		}
+		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,
+		)
 	}
-	sendViaEPIn(
-		ep,
-		&udd_ep_in_cache_buffer[ep][0],
-		count,
-	)
 }
 
-func (usbcdc *USBCDC) handleEndpoint(ep uint32) {
+func handleEndpointRx(ep uint32) []byte {
 	// get data
 	count := int(nrf.USBD.EPOUT[ep].AMOUNT.Get())
 
-	// move to ring buffer
-	for i := 0; i < count; i++ {
-		usbcdc.Receive(byte(udd_ep_out_cache_buffer[ep][i]))
-	}
+	return udd_ep_out_cache_buffer[ep][:count]
+}
 
+func handleEndpointRxComplete(ep uint32) {
 	// set ready for next data
 	nrf.USBD.SIZE.EPOUT[ep].Set(0)
 }
@@ -497,3 +320,47 @@ func handleUSBSetAddress(setup USBSetup) bool {
 	// nrf USBD handles this
 	return true
 }
+
+func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
+	var b [cdcLineInfoSize]byte
+
+	nrf.USBD.TASKS_EP0RCVOUT.Set(1)
+
+	nrf.USBD.EPOUT[0].PTR.Set(uint32(uintptr(unsafe.Pointer(&udd_ep_out_cache_buffer[0]))))
+	nrf.USBD.EPOUT[0].MAXCNT.Set(64)
+
+	timeout := 300000
+	count := 0
+	for {
+		if nrf.USBD.EVENTS_EP0DATADONE.Get() == 1 {
+			nrf.USBD.EVENTS_EP0DATADONE.Set(0)
+			count = int(nrf.USBD.SIZE.EPOUT[0].Get())
+			nrf.USBD.TASKS_STARTEPOUT[0].Set(1)
+			break
+		}
+		timeout--
+		if timeout == 0 {
+			return b, ErrUSBReadTimeout
+		}
+	}
+
+	timeout = 300000
+	for {
+		if nrf.USBD.EVENTS_ENDEPOUT[0].Get() == 1 {
+			nrf.USBD.EVENTS_ENDEPOUT[0].Set(0)
+			break
+		}
+
+		timeout--
+		if timeout == 0 {
+			return b, ErrUSBReadTimeout
+		}
+	}
+
+	nrf.USBD.TASKS_EP0STATUS.Set(1)
+	nrf.USBD.TASKS_EP0RCVOUT.Set(0)
+
+	copy(b[:7], udd_ep_out_cache_buffer[0][:count])
+
+	return b, nil
+}
diff --git a/src/machine/serial-usb.go b/src/machine/serial-usb.go
index 0bec8e297..702cab1ee 100644
--- a/src/machine/serial-usb.go
+++ b/src/machine/serial-usb.go
@@ -4,7 +4,8 @@
 package machine
 
 // Serial is implemented via USB (USB-CDC).
-var Serial = USB
+var Serial Serialer
 
 func InitSerial() {
+	Serial = USBCDC
 }
diff --git a/src/machine/usb.go b/src/machine/usb.go
index ebdacfdaf..3656edc7b 100644
--- a/src/machine/usb.go
+++ b/src/machine/usb.go
@@ -14,25 +14,25 @@ type USBDevice struct {
 
 var (
 	USBDev = &USBDevice{}
+	USBCDC Serialer
 )
+
+type Serialer interface {
+	WriteByte(c byte) error
+	Write(data []byte) (n int, err error)
+	Configure(config UARTConfig) error
+	Buffered() int
+	ReadByte() (byte, error)
+}
+
 var usbDescriptor = descriptorCDC
 
-var (
-	errUSBCDCBufferEmpty      = errors.New("USB-CDC buffer empty")
-	errUSBCDCWriteByteTimeout = errors.New("USB-CDC write byte timeout")
-	errUSBCDCReadTimeout      = errors.New("USB-CDC read timeout")
-	errUSBCDCBytesRead        = errors.New("USB-CDC invalid number of bytes read")
+const (
+	usbDescriptorConfigCDC = 1 << iota
+	usbDescriptorConfigHID
 )
 
-const cdcLineInfoSize = 7
-
-type cdcLineInfo struct {
-	dwDTERate   uint32
-	bCharFormat uint8
-	bParityType uint8
-	bDataBits   uint8
-	lineState   uint8
-}
+var usbDescriptorConfig uint8 = usbDescriptorConfigCDC
 
 // strToUTF16LEDescriptor converts a utf8 string into a string descriptor
 // note: the following code only converts ascii characters to UTF16LE. In order
@@ -54,22 +54,25 @@ var (
 	usb_STRING_LANGUAGE = [2]uint16{(3 << 8) | (2 + 2), 0x0409} // English
 )
 
+const cdcLineInfoSize = 7
+
+var (
+	ErrUSBReadTimeout = errors.New("USB read timeout")
+	ErrUSBBytesRead   = errors.New("USB invalid number of bytes read")
+)
+
 var (
-	usbEndpointDescriptors [8]usbDeviceDescriptor
+	usbEndpointDescriptors [numberOfEndpoints]usbDeviceDescriptor
 
-	udd_ep_in_cache_buffer  [7][128]uint8
-	udd_ep_out_cache_buffer [7][128]uint8
+	udd_ep_control_cache_buffer [256]uint8
+	udd_ep_in_cache_buffer      [7][64]uint8
+	udd_ep_out_cache_buffer     [7][64]uint8
 
 	isEndpointHalt        = false
 	isRemoteWakeUpEnabled = false
-	endPoints             = []uint32{usb_ENDPOINT_TYPE_CONTROL,
-		(usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn),
-		(usb_ENDPOINT_TYPE_BULK | usbEndpointOut),
-		(usb_ENDPOINT_TYPE_BULK | usbEndpointIn)}
 
 	usbConfiguration uint8
 	usbSetInterface  uint8
-	usbLineInfo      = cdcLineInfo{115200, 0x00, 0x00, 0x08, 0x00}
 )
 
 const (
@@ -77,6 +80,7 @@ const (
 	usb_IPRODUCT      = 2
 	usb_ISERIAL       = 3
 
+	usb_ENDPOINT_TYPE_DISABLE     = 0xFF
 	usb_ENDPOINT_TYPE_CONTROL     = 0x00
 	usb_ENDPOINT_TYPE_ISOCHRONOUS = 0x01
 	usb_ENDPOINT_TYPE_BULK        = 0x02
@@ -95,8 +99,8 @@ const (
 	usbEndpointOut = 0x00
 	usbEndpointIn  = 0x80
 
+	numberOfEndpoints     = 8
 	usbEndpointPacketSize = 64 // 64 for Full Speed, EPT size max is 1024
-	usb_EPT_NUM           = 7
 
 	// standard requests
 	usb_GET_STATUS        = 0
@@ -123,12 +127,15 @@ const (
 	usb_CONFIG_SELF_POWERED  = 0xC0
 	usb_CONFIG_REMOTE_WAKEUP = 0x20
 
-	// CDC
+	// Interface
+	numberOfInterfaces     = 3
 	usb_CDC_ACM_INTERFACE  = 0 // CDC ACM
 	usb_CDC_DATA_INTERFACE = 1 // CDC Data
 	usb_CDC_FIRST_ENDPOINT = 1
+	usb_HID_INTERFACE      = 2 // HID
 
 	// Endpoint
+	usb_CONTROL_ENDPOINT = 0
 	usb_CDC_ENDPOINT_ACM = 1
 	usb_CDC_ENDPOINT_OUT = 2
 	usb_CDC_ENDPOINT_IN  = 3
@@ -153,27 +160,20 @@ const (
 	usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE    = (usb_REQUEST_DEVICETOHOST | usb_REQUEST_CLASS | usb_REQUEST_INTERFACE)
 	usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE    = (usb_REQUEST_HOSTTODEVICE | usb_REQUEST_CLASS | usb_REQUEST_INTERFACE)
 	usb_REQUEST_DEVICETOHOST_STANDARD_INTERFACE = (usb_REQUEST_DEVICETOHOST | usb_REQUEST_STANDARD | usb_REQUEST_INTERFACE)
+)
 
-	// CDC Class requests
-	usb_CDC_SET_LINE_CODING        = 0x20
-	usb_CDC_GET_LINE_CODING        = 0x21
-	usb_CDC_SET_CONTROL_LINE_STATE = 0x22
-	usb_CDC_SEND_BREAK             = 0x23
-
-	usb_CDC_V1_10                         = 0x0110
-	usb_CDC_COMMUNICATION_INTERFACE_CLASS = 0x02
-
-	usb_CDC_CALL_MANAGEMENT             = 0x01
-	usb_CDC_ABSTRACT_CONTROL_MODEL      = 0x02
-	usb_CDC_HEADER                      = 0x00
-	usb_CDC_ABSTRACT_CONTROL_MANAGEMENT = 0x02
-	usb_CDC_UNION                       = 0x06
-	usb_CDC_CS_INTERFACE                = 0x24
-	usb_CDC_CS_ENDPOINT                 = 0x25
-	usb_CDC_DATA_INTERFACE_CLASS        = 0x0A
-
-	usb_CDC_LINESTATE_DTR = 0x01
-	usb_CDC_LINESTATE_RTS = 0x02
+var (
+	usbTxHandler    [numberOfEndpoints]func()
+	usbRxHandler    [numberOfEndpoints]func([]byte)
+	usbSetupHandler [numberOfInterfaces]func(USBSetup) bool
+
+	endPoints = []uint32{
+		usb_CONTROL_ENDPOINT: usb_ENDPOINT_TYPE_CONTROL,
+		usb_CDC_ENDPOINT_ACM: (usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn),
+		usb_CDC_ENDPOINT_OUT: (usb_ENDPOINT_TYPE_BULK | usbEndpointOut),
+		usb_CDC_ENDPOINT_IN:  (usb_ENDPOINT_TYPE_BULK | usbEndpointIn),
+		usb_HID_ENDPOINT_IN:  (usb_ENDPOINT_TYPE_DISABLE), // Interrupt In
+	}
 )
 
 // usbDeviceDescBank is the USB device endpoint descriptor.
@@ -209,73 +209,6 @@ func newUSBSetup(data []byte) USBSetup {
 	return u
 }
 
-// USBCDC is the serial interface that works over the USB port.
-// To implement the USBCDC interface for a board, you must declare a concrete type as follows:
-//
-// 		type USBCDC struct {
-// 			Buffer *RingBuffer
-// 		}
-//
-// You can also add additional members to this struct depending on your implementation,
-// but the *RingBuffer is required.
-// When you are declaring the USBCDC for your board, make sure that you also declare the
-// RingBuffer using the NewRingBuffer() function:
-//
-//		USBCDC{Buffer: NewRingBuffer()}
-//
-
-// Read from the RX buffer.
-func (usbcdc *USBCDC) Read(data []byte) (n int, err error) {
-	// check if RX buffer is empty
-	size := usbcdc.Buffered()
-	if size == 0 {
-		return 0, nil
-	}
-
-	// Make sure we do not read more from buffer than the data slice can hold.
-	if len(data) < size {
-		size = len(data)
-	}
-
-	// only read number of bytes used from buffer
-	for i := 0; i < size; i++ {
-		v, _ := usbcdc.ReadByte()
-		data[i] = v
-	}
-
-	return size, nil
-}
-
-// Write data to the USBCDC.
-func (usbcdc *USBCDC) Write(data []byte) (n int, err error) {
-	for _, v := range data {
-		usbcdc.WriteByte(v)
-	}
-	return len(data), nil
-}
-
-// ReadByte reads a single byte from the RX buffer.
-// If there is no data in the buffer, returns an error.
-func (usbcdc *USBCDC) ReadByte() (byte, error) {
-	// check if RX buffer is empty
-	buf, ok := usbcdc.Buffer.Get()
-	if !ok {
-		return 0, errUSBCDCBufferEmpty
-	}
-	return buf, nil
-}
-
-// Buffered returns the number of bytes currently stored in the RX buffer.
-func (usbcdc *USBCDC) Buffered() int {
-	return int(usbcdc.Buffer.Used())
-}
-
-// Receive handles adding data to the UART's data buffer.
-// Usually called by the IRQ handler for a machine.
-func (usbcdc *USBCDC) Receive(data byte) {
-	usbcdc.Buffer.Put(data)
-}
-
 // sendDescriptor creates and sends the various USB descriptor types that
 // can be requested by the host.
 func sendDescriptor(setup USBSetup) {
@@ -285,6 +218,11 @@ func sendDescriptor(setup USBSetup) {
 		return
 	case usb_DEVICE_DESCRIPTOR_TYPE:
 		// composite descriptor
+		if (usbDescriptorConfig & usbDescriptorConfigHID) > 0 {
+			usbDescriptor = descriptorCDCHID
+		} else {
+			usbDescriptor = descriptorCDC
+		}
 		usbDescriptor.Configure(usb_VID, usb_PID)
 		sendUSBPacket(0, usbDescriptor.Device, setup.WLength)
 		return
@@ -402,17 +340,21 @@ func handleStandardSetup(setup USBSetup) bool {
 	}
 }
 
-// EnableHID enables HID. This function must be executed from the init().
-func EnableHID(callback func()) {
-	usbDescriptor = descriptorCDCHID
-	endPoints = []uint32{usb_ENDPOINT_TYPE_CONTROL,
-		(usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn),
-		(usb_ENDPOINT_TYPE_BULK | usbEndpointOut),
-		(usb_ENDPOINT_TYPE_BULK | usbEndpointIn),
-		(usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn)}
-
-	hidCallback = callback
+func EnableCDC(txHandler func(), rxHandler func([]byte), setupHandler func(USBSetup) bool) {
+	usbDescriptorConfig |= usbDescriptorConfigCDC
+	endPoints[usb_CDC_ENDPOINT_ACM] = (usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn)
+	endPoints[usb_CDC_ENDPOINT_OUT] = (usb_ENDPOINT_TYPE_BULK | usbEndpointOut)
+	endPoints[usb_CDC_ENDPOINT_IN] = (usb_ENDPOINT_TYPE_BULK | usbEndpointIn)
+	usbRxHandler[usb_CDC_ENDPOINT_OUT] = rxHandler
+	usbTxHandler[usb_CDC_ENDPOINT_IN] = txHandler
+	usbSetupHandler[usb_CDC_ACM_INTERFACE] = setupHandler // 0x02 (Communications and CDC Control)
+	usbSetupHandler[usb_CDC_DATA_INTERFACE] = nil         // 0x0A (CDC-Data)
 }
 
-// hidCallback is a variable that holds the callback when using HID.
-var hidCallback func()
+// EnableHID enables HID. This function must be executed from the init().
+func EnableHID(txHandler func(), rxHandler func([]byte), setupHandler func(USBSetup) bool) {
+	usbDescriptorConfig |= usbDescriptorConfigHID
+	endPoints[usb_HID_ENDPOINT_IN] = (usb_ENDPOINT_TYPE_INTERRUPT | usbEndpointIn)
+	usbTxHandler[usb_HID_ENDPOINT_IN] = txHandler
+	usbSetupHandler[usb_HID_INTERFACE] = setupHandler // 0x03 (HID - Human Interface Device)
+}
diff --git a/src/machine/usb/cdc/buffer.go b/src/machine/usb/cdc/buffer.go
new file mode 100644
index 000000000..ad5eb3645
--- /dev/null
+++ b/src/machine/usb/cdc/buffer.go
@@ -0,0 +1,119 @@
+package cdc
+
+import (
+	"runtime/volatile"
+)
+
+const rxRingBufferSize = 128
+
+// rxRingBuffer is ring buffer implementation inspired by post at
+// https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
+type rxRingBuffer struct {
+	buffer [rxRingBufferSize]volatile.Register8
+	head   volatile.Register8
+	tail   volatile.Register8
+}
+
+// NewRxRingBuffer returns a new ring buffer.
+func NewRxRingBuffer() *rxRingBuffer {
+	return &rxRingBuffer{}
+}
+
+// Used returns how many bytes in buffer have been used.
+func (rb *rxRingBuffer) Used() uint8 {
+	return uint8(rb.head.Get() - rb.tail.Get())
+}
+
+// Put stores a byte in the buffer. If the buffer is already
+// full, the method will return false.
+func (rb *rxRingBuffer) Put(val byte) bool {
+	if rb.Used() != rxRingBufferSize {
+		rb.head.Set(rb.head.Get() + 1)
+		rb.buffer[rb.head.Get()%rxRingBufferSize].Set(val)
+		return true
+	}
+	return false
+}
+
+// Get returns a byte from the buffer. If the buffer is empty,
+// the method will return a false as the second value.
+func (rb *rxRingBuffer) Get() (byte, bool) {
+	if rb.Used() != 0 {
+		rb.tail.Set(rb.tail.Get() + 1)
+		return rb.buffer[rb.tail.Get()%rxRingBufferSize].Get(), true
+	}
+	return 0, false
+}
+
+// Clear resets the head and tail pointer to zero.
+func (rb *rxRingBuffer) Clear() {
+	rb.head.Set(0)
+	rb.tail.Set(0)
+}
+
+const txRingBufferSize = 8
+
+// txRingBuffer is ring buffer implementation inspired by post at
+// https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
+type txRingBuffer struct {
+	buffer [txRingBufferSize]struct {
+		buf  [64]byte
+		size int
+	}
+	head volatile.Register8
+	tail volatile.Register8
+}
+
+// NewTxRingBuffer returns a new ring buffer.
+func NewTxRingBuffer() *txRingBuffer {
+	return &txRingBuffer{}
+}
+
+// Used returns how many bytes in buffer have been used.
+func (rb *txRingBuffer) Used() uint8 {
+	return uint8(rb.head.Get() - rb.tail.Get())
+}
+
+// Put stores a byte in the buffer. If the buffer is already
+// full, the method will return false.
+func (rb *txRingBuffer) Put(val []byte) bool {
+	if rb.Used() == txRingBufferSize {
+		return false
+	}
+
+	if rb.Used() == 0 {
+		rb.head.Set(rb.head.Get() + 1)
+		rb.buffer[rb.head.Get()%txRingBufferSize].size = 0
+	}
+	buf := &rb.buffer[rb.head.Get()%txRingBufferSize]
+
+	for i := 0; i < len(val); i++ {
+		if buf.size == 64 {
+			// next
+			// TODO: Make sure that data is not corrupted even when the buffer is full
+			rb.head.Set(rb.head.Get() + 1)
+			buf = &rb.buffer[rb.head.Get()%txRingBufferSize]
+			rb.buffer[rb.head.Get()%txRingBufferSize].size = 0
+		}
+		buf.buf[buf.size] = val[i]
+		buf.size++
+	}
+	return true
+}
+
+// Get returns a byte from the buffer. If the buffer is empty,
+// the method will return a false as the second value.
+func (rb *txRingBuffer) Get() ([]byte, bool) {
+	if rb.Used() != 0 {
+		rb.tail.Set(rb.tail.Get() + 1)
+		size := rb.buffer[rb.tail.Get()%txRingBufferSize].size
+		return rb.buffer[rb.tail.Get()%txRingBufferSize].buf[:size], true
+	}
+	return nil, false
+}
+
+// Clear resets the head and tail pointer to zero.
+func (rb *txRingBuffer) Clear() {
+	rb.head.Set(0)
+	rb.tail.Set(0)
+}
diff --git a/src/machine/usb/cdc/cdc.go b/src/machine/usb/cdc/cdc.go
new file mode 100644
index 000000000..f180535df
--- /dev/null
+++ b/src/machine/usb/cdc/cdc.go
@@ -0,0 +1,61 @@
+package cdc
+
+const (
+	cdcEndpointACM = 1
+	cdcEndpointOut = 2
+	cdcEndpointIn  = 3
+)
+
+// New returns USBCDC struct.
+func New() *USBCDC {
+	if USB == nil {
+		USB = &USBCDC{
+			rxBuffer: NewRxRingBuffer(),
+			txBuffer: NewTxRingBuffer(),
+		}
+	}
+	return USB
+}
+
+const (
+	// bmRequestType
+	usb_REQUEST_HOSTTODEVICE = 0x00
+	usb_REQUEST_DEVICETOHOST = 0x80
+	usb_REQUEST_DIRECTION    = 0x80
+
+	usb_REQUEST_STANDARD = 0x00
+	usb_REQUEST_CLASS    = 0x20
+	usb_REQUEST_VENDOR   = 0x40
+	usb_REQUEST_TYPE     = 0x60
+
+	usb_REQUEST_DEVICE    = 0x00
+	usb_REQUEST_INTERFACE = 0x01
+	usb_REQUEST_ENDPOINT  = 0x02
+	usb_REQUEST_OTHER     = 0x03
+	usb_REQUEST_RECIPIENT = 0x1F
+
+	usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE    = (usb_REQUEST_DEVICETOHOST | usb_REQUEST_CLASS | usb_REQUEST_INTERFACE)
+	usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE    = (usb_REQUEST_HOSTTODEVICE | usb_REQUEST_CLASS | usb_REQUEST_INTERFACE)
+	usb_REQUEST_DEVICETOHOST_STANDARD_INTERFACE = (usb_REQUEST_DEVICETOHOST | usb_REQUEST_STANDARD | usb_REQUEST_INTERFACE)
+
+	// CDC Class requests
+	usb_CDC_SET_LINE_CODING        = 0x20
+	usb_CDC_GET_LINE_CODING        = 0x21
+	usb_CDC_SET_CONTROL_LINE_STATE = 0x22
+	usb_CDC_SEND_BREAK             = 0x23
+
+	usb_CDC_V1_10                         = 0x0110
+	usb_CDC_COMMUNICATION_INTERFACE_CLASS = 0x02
+
+	usb_CDC_CALL_MANAGEMENT             = 0x01
+	usb_CDC_ABSTRACT_CONTROL_MODEL      = 0x02
+	usb_CDC_HEADER                      = 0x00
+	usb_CDC_ABSTRACT_CONTROL_MANAGEMENT = 0x02
+	usb_CDC_UNION                       = 0x06
+	usb_CDC_CS_INTERFACE                = 0x24
+	usb_CDC_CS_ENDPOINT                 = 0x25
+	usb_CDC_DATA_INTERFACE_CLASS        = 0x0A
+
+	usb_CDC_LINESTATE_DTR = 0x01
+	usb_CDC_LINESTATE_RTS = 0x02
+)
diff --git a/src/machine/usb/cdc/usbcdc.go b/src/machine/usb/cdc/usbcdc.go
new file mode 100644
index 000000000..a21089688
--- /dev/null
+++ b/src/machine/usb/cdc/usbcdc.go
@@ -0,0 +1,189 @@
+package cdc
+
+import (
+	"errors"
+	"machine"
+	"runtime/interrupt"
+)
+
+var (
+	ErrBufferEmpty = errors.New("USB-CDC buffer empty")
+)
+
+const cdcLineInfoSize = 7
+
+type cdcLineInfo struct {
+	dwDTERate   uint32
+	bCharFormat uint8
+	bParityType uint8
+	bDataBits   uint8
+	lineState   uint8
+}
+
+// Read from the RX buffer.
+func (usbcdc *USBCDC) Read(data []byte) (n int, err error) {
+	// check if RX buffer is empty
+	size := usbcdc.Buffered()
+	if size == 0 {
+		return 0, nil
+	}
+
+	// Make sure we do not read more from buffer than the data slice can hold.
+	if len(data) < size {
+		size = len(data)
+	}
+
+	// only read number of bytes used from buffer
+	for i := 0; i < size; i++ {
+		v, _ := usbcdc.ReadByte()
+		data[i] = v
+	}
+
+	return size, nil
+}
+
+// ReadByte reads a single byte from the RX buffer.
+// If there is no data in the buffer, returns an error.
+func (usbcdc *USBCDC) ReadByte() (byte, error) {
+	// check if RX buffer is empty
+	buf, ok := usbcdc.rxBuffer.Get()
+	if !ok {
+		return 0, ErrBufferEmpty
+	}
+	return buf, nil
+}
+
+// Buffered returns the number of bytes currently stored in the RX buffer.
+func (usbcdc *USBCDC) Buffered() int {
+	return int(usbcdc.rxBuffer.Used())
+}
+
+// Receive handles adding data to the UART's data buffer.
+// Usually called by the IRQ handler for a machine.
+func (usbcdc *USBCDC) Receive(data byte) {
+	usbcdc.rxBuffer.Put(data)
+}
+
+// USBCDC is the USB CDC aka serial over USB interface.
+type USBCDC struct {
+	rxBuffer *rxRingBuffer
+	txBuffer *txRingBuffer
+	waitTxc  bool
+}
+
+var (
+	// USB is a USB CDC interface.
+	USB *USBCDC
+
+	usbLineInfo = cdcLineInfo{115200, 0x00, 0x00, 0x08, 0x00}
+)
+
+// Configure the USB CDC interface. The config is here for compatibility with the UART interface.
+func (usbcdc *USBCDC) Configure(config machine.UARTConfig) error {
+	return nil
+}
+
+// Flush flushes buffered data.
+func (usbcdc *USBCDC) Flush() {
+	mask := interrupt.Disable()
+	if b, ok := usbcdc.txBuffer.Get(); ok {
+		machine.SendUSBInPacket(cdcEndpointIn, b)
+	} else {
+		usbcdc.waitTxc = false
+	}
+	interrupt.Restore(mask)
+}
+
+// Write data to the USBCDC.
+func (usbcdc *USBCDC) Write(data []byte) (n int, err error) {
+	if usbLineInfo.lineState > 0 {
+		mask := interrupt.Disable()
+		usbcdc.txBuffer.Put(data)
+		if !usbcdc.waitTxc {
+			usbcdc.waitTxc = true
+			usbcdc.Flush()
+		}
+		interrupt.Restore(mask)
+	}
+	return len(data), nil
+}
+
+// WriteByte writes a byte of data to the USB CDC interface.
+func (usbcdc *USBCDC) WriteByte(c byte) error {
+	usbcdc.Write([]byte{c})
+	return nil
+}
+
+func (usbcdc *USBCDC) DTR() bool {
+	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
+}
+
+func (usbcdc *USBCDC) RTS() bool {
+	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
+}
+
+func cdcCallbackRx(b []byte) {
+	for i := range b {
+		USB.Receive(b[i])
+	}
+}
+
+func cdcSetup(setup machine.USBSetup) bool {
+	if setup.BmRequestType == usb_REQUEST_DEVICETOHOST_CLASS_INTERFACE {
+		if setup.BRequest == usb_CDC_GET_LINE_CODING {
+			var b [cdcLineInfoSize]byte
+			b[0] = byte(usbLineInfo.dwDTERate)
+			b[1] = byte(usbLineInfo.dwDTERate >> 8)
+			b[2] = byte(usbLineInfo.dwDTERate >> 16)
+			b[3] = byte(usbLineInfo.dwDTERate >> 24)
+			b[4] = byte(usbLineInfo.bCharFormat)
+			b[5] = byte(usbLineInfo.bParityType)
+			b[6] = byte(usbLineInfo.bDataBits)
+
+			machine.SendUSBInPacket(0, b[:])
+			return true
+		}
+	}
+
+	if setup.BmRequestType == usb_REQUEST_HOSTTODEVICE_CLASS_INTERFACE {
+		if setup.BRequest == usb_CDC_SET_LINE_CODING {
+			b, err := machine.ReceiveUSBControlPacket()
+			if err != nil {
+				return false
+			}
+
+			usbLineInfo.dwDTERate = uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+			usbLineInfo.bCharFormat = b[4]
+			usbLineInfo.bParityType = b[5]
+			usbLineInfo.bDataBits = b[6]
+		}
+
+		if setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
+			usbLineInfo.lineState = setup.WValueL
+		}
+
+		if setup.BRequest == usb_CDC_SET_LINE_CODING || setup.BRequest == usb_CDC_SET_CONTROL_LINE_STATE {
+			// auto-reset into the bootloader
+			if usbLineInfo.dwDTERate == 1200 && usbLineInfo.lineState&usb_CDC_LINESTATE_DTR == 0 {
+				machine.EnterBootloader()
+			} else {
+				// TODO: cancel any reset
+			}
+			machine.SendZlp()
+		}
+
+		if setup.BRequest == usb_CDC_SEND_BREAK {
+			// TODO: something with this value?
+			// breakValue = ((uint16_t)setup.wValueH << 8) | setup.wValueL;
+			// return false;
+			machine.SendZlp()
+		}
+		return true
+	}
+	return false
+}
+
+func EnableUSBCDC() {
+	machine.USBCDC = New()
+	machine.EnableCDC(USB.Flush, cdcCallbackRx, cdcSetup)
+}
diff --git a/src/machine/usb/hid/hid.go b/src/machine/usb/hid/hid.go
index fd9317511..1429dab2b 100644
--- a/src/machine/usb/hid/hid.go
+++ b/src/machine/usb/hid/hid.go
@@ -14,6 +14,9 @@ var (
 
 const (
 	hidEndpoint = 4
+
+	usb_SET_REPORT_TYPE = 33
+	usb_SET_IDLE        = 10
 )
 
 type hidDevicer interface {
@@ -27,7 +30,7 @@ var size int
 // calls machine.EnableHID for USB configuration
 func SetCallbackHandler(d hidDevicer) {
 	if size == 0 {
-		machine.EnableHID(callback)
+		machine.EnableHID(callback, nil, callbackSetup)
 	}
 
 	devices[size] = d
@@ -45,7 +48,16 @@ func callback() {
 	}
 }
 
+func callbackSetup(setup machine.USBSetup) bool {
+	ok := false
+	if setup.BmRequestType == usb_SET_REPORT_TYPE && setup.BRequest == usb_SET_IDLE {
+		machine.SendZlp()
+		ok = true
+	}
+	return ok
+}
+
 // SendUSBPacket sends a HIDPacket.
 func SendUSBPacket(b []byte) {
-	machine.SendUSBHIDPacket(hidEndpoint, b)
+	machine.SendUSBInPacket(hidEndpoint, b)
 }
diff --git a/src/machine/usb/hid/keyboard/keyboard.go b/src/machine/usb/hid/keyboard/keyboard.go
index 1f5643385..77dacf688 100644
--- a/src/machine/usb/hid/keyboard/keyboard.go
+++ b/src/machine/usb/hid/keyboard/keyboard.go
@@ -41,7 +41,8 @@ type keyboard struct {
 	// wideChar holds high bits for the UTF-8 decoder.
 	wideChar uint16
 
-	buf *hid.RingBuffer
+	buf     *hid.RingBuffer
+	waitTxc bool
 }
 
 // decodeState represents a state in the UTF-8 decode state machine.
@@ -74,13 +75,24 @@ func newKeyboard() *keyboard {
 }
 
 func (kb *keyboard) Callback() bool {
+	kb.waitTxc = false
 	if b, ok := kb.buf.Get(); ok {
+		kb.waitTxc = true
 		hid.SendUSBPacket(b)
 		return true
 	}
 	return false
 }
 
+func (kb *keyboard) tx(b []byte) {
+	if kb.waitTxc {
+		kb.buf.Put(b)
+	} else {
+		kb.waitTxc = true
+		hid.SendUSBPacket(b)
+	}
+}
+
 func (kb *keyboard) ready() bool {
 	return true
 }
@@ -214,7 +226,7 @@ func (kb *keyboard) Press(c Keycode) error {
 }
 
 func (kb *keyboard) sendKey(consumer bool, b []byte) bool {
-	kb.buf.Put(b)
+	kb.tx(b)
 	return true
 }
 
diff --git a/src/machine/usb/hid/mouse/mouse.go b/src/machine/usb/hid/mouse/mouse.go
index 49a189f50..bc079c96a 100644
--- a/src/machine/usb/hid/mouse/mouse.go
+++ b/src/machine/usb/hid/mouse/mouse.go
@@ -15,8 +15,9 @@ const (
 )
 
 type mouse struct {
-	buf    *hid.RingBuffer
-	button Button
+	buf     *hid.RingBuffer
+	button  Button
+	waitTxc bool
 }
 
 func init() {
@@ -38,13 +39,24 @@ func newMouse() *mouse {
 }
 
 func (m *mouse) Callback() bool {
+	m.waitTxc = false
 	if b, ok := m.buf.Get(); ok {
+		m.waitTxc = true
 		hid.SendUSBPacket(b[:5])
 		return true
 	}
 	return false
 }
 
+func (m *mouse) tx(b []byte) {
+	if m.waitTxc {
+		m.buf.Put(b)
+	} else {
+		m.waitTxc = true
+		hid.SendUSBPacket(b)
+	}
+}
+
 // Move is a function that moves the mouse cursor.
 func (m *mouse) Move(vx, vy int) {
 	if vx == 0 && vy == 0 {
@@ -65,7 +77,7 @@ func (m *mouse) Move(vx, vy int) {
 		vy = 127
 	}
 
-	m.buf.Put([]byte{
+	m.tx([]byte{
 		0x01, byte(m.button), byte(vx), byte(vy), 0x00,
 	})
 }
@@ -79,7 +91,7 @@ func (m *mouse) Click(btn Button) {
 // Press presses the given mouse buttons.
 func (m *mouse) Press(btn Button) {
 	m.button |= btn
-	m.buf.Put([]byte{
+	m.tx([]byte{
 		0x01, byte(m.button), 0x00, 0x00, 0x00,
 	})
 }
@@ -87,7 +99,7 @@ func (m *mouse) Press(btn Button) {
 // Release releases the given mouse buttons.
 func (m *mouse) Release(btn Button) {
 	m.button &= ^btn
-	m.buf.Put([]byte{
+	m.tx([]byte{
 		0x01, byte(m.button), 0x00, 0x00, 0x00,
 	})
 }
@@ -105,7 +117,7 @@ func (m *mouse) Wheel(v int) {
 		v = 127
 	}
 
-	m.buf.Put([]byte{
+	m.tx([]byte{
 		0x01, byte(m.button), 0x00, 0x00, byte(v),
 	})
 }
diff --git a/src/machine/usb_descriptor.go b/src/machine/usb_descriptor.go
index 9a1220c42..4489a546b 100644
--- a/src/machine/usb_descriptor.go
+++ b/src/machine/usb_descriptor.go
@@ -14,6 +14,9 @@ func (d *USBDescriptor) Configure(idVendor, idProduct uint16) {
 	d.Device[9] = byte(idVendor >> 8)
 	d.Device[10] = byte(idProduct)
 	d.Device[11] = byte(idProduct >> 8)
+
+	d.Configuration[2] = byte(len(d.Configuration))
+	d.Configuration[3] = byte(len(d.Configuration) >> 8)
 }
 
 var descriptorCDC = USBDescriptor{
diff --git a/src/runtime/runtime_atsamd21.go b/src/runtime/runtime_atsamd21.go
index df0e8a493..0f411366b 100644
--- a/src/runtime/runtime_atsamd21.go
+++ b/src/runtime/runtime_atsamd21.go
@@ -7,6 +7,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"machine"
+	"machine/usb/cdc"
 	"runtime/interrupt"
 	"runtime/volatile"
 	"unsafe"
@@ -28,6 +29,7 @@ func init() {
 	initUSBClock()
 	initADCClock()
 
+	cdc.EnableUSBCDC()
 	machine.USBDev.Configure(machine.UARTConfig{})
 	machine.InitSerial()
 }
diff --git a/src/runtime/runtime_atsamd51.go b/src/runtime/runtime_atsamd51.go
index cb29d9650..f1e585ee2 100644
--- a/src/runtime/runtime_atsamd51.go
+++ b/src/runtime/runtime_atsamd51.go
@@ -7,6 +7,7 @@ import (
 	"device/arm"
 	"device/sam"
 	"machine"
+	"machine/usb/cdc"
 	"runtime/interrupt"
 	"runtime/volatile"
 )
@@ -28,6 +29,7 @@ func init() {
 	initUSBClock()
 	initADCClock()
 
+	cdc.EnableUSBCDC()
 	machine.USBDev.Configure(machine.UARTConfig{})
 	machine.InitSerial()
 }
diff --git a/src/runtime/runtime_nrf52840.go b/src/runtime/runtime_nrf52840.go
index a4907b925..cd1d892e5 100644
--- a/src/runtime/runtime_nrf52840.go
+++ b/src/runtime/runtime_nrf52840.go
@@ -7,6 +7,7 @@ import (
 	"device/arm"
 	"device/nrf"
 	"machine"
+	"machine/usb/cdc"
 	"runtime/interrupt"
 	"runtime/volatile"
 )
@@ -28,6 +29,7 @@ func main() {
 }
 
 func init() {
+	cdc.EnableUSBCDC()
 	machine.USBDev.Configure(machine.UARTConfig{})
 	machine.InitSerial()
 	initLFCLK()