support multi-port CDC devices

test/arduino_leonardo_bridge_castrated_cdc/CDC.cpp

@@ -0,0 +1,303 @@
+
+
+/* Copyright (c) 2011, Peter Barrett  
+**  
+** Permission to use, copy, modify, and/or distribute this software for  
+** any purpose with or without fee is hereby granted, provided that the  
+** above copyright notice and this permission notice appear in all copies.  
+** 
+** THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL  
+** WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED  
+** WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR  
+** BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES  
+** OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,  
+** WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,  
+** ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS  
+** SOFTWARE.  
+*/
+
+#include "USBCore.h" // kai:added
+#include "USBAPI.h"
+#include <avr/wdt.h>
+#include <util/atomic.h>
+
+#if defined(USBCON)
+
+typedef struct
+{
+	u32	dwDTERate;
+	u8	bCharFormat;
+	u8 	bParityType;
+	u8 	bDataBits;
+	u8	lineState;
+} LineInfo;
+
+static volatile LineInfo _usbLineInfo = { 57600, 0x00, 0x00, 0x00, 0x00 };
+static volatile int32_t breakValue = -1;
+
+static u8 wdtcsr_save;
+
+#define WEAK __attribute__ ((weak))
+
+extern const CDCDescriptor _cdcInterface PROGMEM;
+const CDCDescriptor _cdcInterface =
+{
+	D_IAD(0,2,CDC_COMMUNICATION_INTERFACE_CLASS,CDC_ABSTRACT_CONTROL_MODEL,1),
+
+	//	CDC communication interface
+	D_INTERFACE(CDC_ACM_INTERFACE,3,CDC_COMMUNICATION_INTERFACE_CLASS,CDC_ABSTRACT_CONTROL_MODEL,0), // kai
+	D_CDCCS(CDC_HEADER,0x10,0x01),								// Header (1.10 bcd)
+	D_CDCCS(CDC_CALL_MANAGEMENT,1,1),							// Device handles call management (not)
+	D_CDCCS4(CDC_ABSTRACT_CONTROL_MANAGEMENT,6),				// SET_LINE_CODING, GET_LINE_CODING, SET_CONTROL_LINE_STATE supported
+	D_CDCCS(CDC_UNION,CDC_ACM_INTERFACE,CDC_DATA_INTERFACE),	// Communication interface is master, data interface is slave 0
+	D_ENDPOINT(USB_ENDPOINT_IN (CDC_ENDPOINT_ACM),USB_ENDPOINT_TYPE_INTERRUPT,0x10,0x40),
+
+	//	CDC data interface
+	//D_INTERFACE(CDC_DATA_INTERFACE,2,CDC_DATA_INTERFACE_CLASS,0,0), // kai:removed
+	D_ENDPOINT(USB_ENDPOINT_OUT(CDC_ENDPOINT_OUT),USB_ENDPOINT_TYPE_BULK,USB_EP_SIZE,0),
+	D_ENDPOINT(USB_ENDPOINT_IN (CDC_ENDPOINT_IN ),USB_ENDPOINT_TYPE_BULK,USB_EP_SIZE,0)
+};
+
+bool isLUFAbootloader()
+{
+	return pgm_read_word(FLASHEND - 1) == NEW_LUFA_SIGNATURE;
+}
+
+int CDC_GetInterface(u8* interfaceNum)
+{
+	interfaceNum[0] += 1;	// kai
+	return USB_SendControl(TRANSFER_PGM,&_cdcInterface,sizeof(_cdcInterface));
+}
+
+bool CDC_Setup(USBSetup& setup)
+{
+	u8 r = setup.bRequest;
+	u8 requestType = setup.bmRequestType;
+
+	if (REQUEST_DEVICETOHOST_CLASS_INTERFACE == requestType)
+	{
+		if (CDC_GET_LINE_CODING == r)
+		{
+			USB_SendControl(0,(void*)&_usbLineInfo,7);
+			return true;
+		}
+	}
+
+	if (REQUEST_HOSTTODEVICE_CLASS_INTERFACE == requestType)
+	{
+		if (CDC_SEND_BREAK == r)
+		{
+			breakValue = ((uint16_t)setup.wValueH << 8) | setup.wValueL;
+		}
+
+		if (CDC_SET_LINE_CODING == r)
+		{
+			USB_RecvControl((void*)&_usbLineInfo,7);
+		}
+
+		if (CDC_SET_CONTROL_LINE_STATE == r)
+		{
+			_usbLineInfo.lineState = setup.wValueL;
+
+			// auto-reset into the bootloader is triggered when the port, already 
+			// open at 1200 bps, is closed.  this is the signal to start the watchdog
+			// with a relatively long period so it can finish housekeeping tasks
+			// like servicing endpoints before the sketch ends
+
+			uint16_t magic_key_pos = MAGIC_KEY_POS;
+
+// If we don't use the new RAMEND directly, check manually if we have a newer bootloader.
+// This is used to keep compatible with the old leonardo bootloaders.
+// You are still able to set the magic key position manually to RAMEND-1 to save a few bytes for this check.
+#if MAGIC_KEY_POS != (RAMEND-1)
+			// For future boards save the key in the inproblematic RAMEND
+			// Which is reserved for the main() return value (which will never return)
+			if (isLUFAbootloader()) {
+				// horray, we got a new bootloader!
+				magic_key_pos = (RAMEND-1);
+			}
+#endif
+
+			// We check DTR state to determine if host port is open (bit 0 of lineState).
+			if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
+			{
+#if MAGIC_KEY_POS != (RAMEND-1)
+				// Backup ram value if its not a newer bootloader and it hasn't already been saved.
+				// This should avoid memory corruption at least a bit, not fully
+				if (magic_key_pos != (RAMEND-1) && *(uint16_t *)magic_key_pos != MAGIC_KEY) {
+					*(uint16_t *)(RAMEND-1) = *(uint16_t *)magic_key_pos;
+				}
+#endif
+				// Store boot key
+				*(uint16_t *)magic_key_pos = MAGIC_KEY;
+				// Save the watchdog state in case the reset is aborted.
+				wdtcsr_save = WDTCSR;
+				wdt_enable(WDTO_120MS);
+			}
+			else if (*(uint16_t *)magic_key_pos == MAGIC_KEY)
+			{
+				// Most OSs do some intermediate steps when configuring ports and DTR can
+				// twiggle more than once before stabilizing.
+				// To avoid spurious resets we set the watchdog to 120ms and eventually
+				// cancel if DTR goes back high.
+				// Cancellation is only done if an auto-reset was started, which is
+				// indicated by the magic key having been set.
+
+				wdt_reset();
+				// Restore the watchdog state in case the sketch was using it.
+				WDTCSR |= (1<<WDCE) | (1<<WDE);
+				WDTCSR = wdtcsr_save;
+#if MAGIC_KEY_POS != (RAMEND-1)
+				// Restore backed up (old bootloader) magic key data
+				if (magic_key_pos != (RAMEND-1)) {
+					*(uint16_t *)magic_key_pos = *(uint16_t *)(RAMEND-1);
+				} else
+#endif
+				{
+				// Clean up RAMEND key
+					*(uint16_t *)magic_key_pos = 0x0000;
+				}
+			}
+		}
+		return true;
+	}
+	return false;
+}
+
+
+void Serial_::begin(unsigned long /* baud_count */)
+{
+	peek_buffer = -1;
+}
+
+void Serial_::begin(unsigned long /* baud_count */, byte /* config */)
+{
+	peek_buffer = -1;
+}
+
+void Serial_::end(void)
+{
+}
+
+int Serial_::available(void)
+{
+	if (peek_buffer >= 0) {
+		return 1 + USB_Available(CDC_RX);
+	}
+	return USB_Available(CDC_RX);
+}
+
+int Serial_::peek(void)
+{
+	if (peek_buffer < 0)
+		peek_buffer = USB_Recv(CDC_RX);
+	return peek_buffer;
+}
+
+int Serial_::read(void)
+{
+	if (peek_buffer >= 0) {
+		int c = peek_buffer;
+		peek_buffer = -1;
+		return c;
+	}
+	return USB_Recv(CDC_RX);
+}
+
+int Serial_::availableForWrite(void)
+{
+	return USB_SendSpace(CDC_TX);
+}
+
+void Serial_::flush(void)
+{
+	USB_Flush(CDC_TX);
+}
+
+size_t Serial_::write(uint8_t c)
+{
+	return write(&c, 1);
+}
+
+size_t Serial_::write(const uint8_t *buffer, size_t size)
+{
+	/* only try to send bytes if the high-level CDC connection itself 
+	 is open (not just the pipe) - the OS should set lineState when the port
+	 is opened and clear lineState when the port is closed.
+	 bytes sent before the user opens the connection or after
+	 the connection is closed are lost - just like with a UART. */
+	
+	// TODO - ZE - check behavior on different OSes and test what happens if an
+	// open connection isn't broken cleanly (cable is yanked out, host dies
+	// or locks up, or host virtual serial port hangs)
+	if (_usbLineInfo.lineState > 0)	{
+		int r = USB_Send(CDC_TX,buffer,size);
+		if (r > 0) {
+			return r;
+		} else {
+			setWriteError();
+			return 0;
+		}
+	}
+	setWriteError();
+	return 0;
+}
+
+// This operator is a convenient way for a sketch to check whether the
+// port has actually been configured and opened by the host (as opposed
+// to just being connected to the host).  It can be used, for example, in 
+// setup() before printing to ensure that an application on the host is
+// actually ready to receive and display the data.
+// We add a short delay before returning to fix a bug observed by Federico
+// where the port is configured (lineState != 0) but not quite opened.
+Serial_::operator bool() {
+	bool result = false;
+	if (_usbLineInfo.lineState > 0) 
+		result = true;
+	delay(10);
+	return result;
+}
+
+unsigned long Serial_::baud() {
+	// Disable interrupts while reading a multi-byte value
+	uint32_t baudrate;
+	ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+		baudrate =  _usbLineInfo.dwDTERate;
+	}
+	return baudrate;
+}
+
+uint8_t Serial_::stopbits() {
+	return _usbLineInfo.bCharFormat;
+}
+
+uint8_t Serial_::paritytype() {
+	return _usbLineInfo.bParityType;
+}
+
+uint8_t Serial_::numbits() {
+	return _usbLineInfo.bDataBits;
+}
+
+bool Serial_::dtr() {
+	return _usbLineInfo.lineState & 0x1;
+}
+
+bool Serial_::rts() {
+	return _usbLineInfo.lineState & 0x2;
+}
+
+int32_t Serial_::readBreak() {
+	int32_t ret;
+	// Disable IRQs while reading and clearing breakValue to make
+	// sure we don't overwrite a value just set by the ISR.
+	ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
+		ret = breakValue;
+		breakValue = -1;
+	}
+	return ret;
+}
+
+Serial_ Serial;
+
+#endif /* if defined(USBCON) */

test/arduino_leonardo_bridge_castrated_cdc/README.md

@@ -0,0 +1,8 @@
+## castrated CDC test (single interface with 3 endpoints)
+
+As mentioned [here](https://arduino.stackexchange.com/a/31695/62145), Arduino functions can be _overwritten_ by copying complete files into the own project. 
+
+This is used to create a castrated CDC device with a single interface containing 3 endpoints. 
+
+The modifications have been done against Arduino 1.8.10, for changes see comments containing `kai`.
+

test/arduino_leonardo_bridge_castrated_cdc/USBCore.h

@@ -0,0 +1,301 @@
+
+// Copyright (c) 2010, Peter Barrett 
+/*
+** Permission to use, copy, modify, and/or distribute this software for  
+** any purpose with or without fee is hereby granted, provided that the  
+** above copyright notice and this permission notice appear in all copies.  
+**  
+** THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL  
+** WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED  
+** WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR  
+** BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES  
+** OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,  
+** WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,  
+** ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS  
+** SOFTWARE.  
+*/
+
+#ifndef __USBCORE_H__
+#define __USBCORE_H__
+
+#include "USBAPI.h"
+
+//	Standard requests
+#define GET_STATUS			0
+#define CLEAR_FEATURE		1
+#define SET_FEATURE			3
+#define SET_ADDRESS			5
+#define GET_DESCRIPTOR		6
+#define SET_DESCRIPTOR		7
+#define GET_CONFIGURATION	8
+#define SET_CONFIGURATION	9
+#define GET_INTERFACE		10
+#define SET_INTERFACE		11
+
+
+// bmRequestType
+#define REQUEST_HOSTTODEVICE	0x00
+#define REQUEST_DEVICETOHOST	0x80
+#define REQUEST_DIRECTION		0x80
+
+#define REQUEST_STANDARD		0x00
+#define REQUEST_CLASS			0x20
+#define REQUEST_VENDOR			0x40
+#define REQUEST_TYPE			0x60
+
+#define REQUEST_DEVICE			0x00
+#define REQUEST_INTERFACE		0x01
+#define REQUEST_ENDPOINT		0x02
+#define REQUEST_OTHER			0x03
+#define REQUEST_RECIPIENT		0x03
+
+#define REQUEST_DEVICETOHOST_CLASS_INTERFACE    (REQUEST_DEVICETOHOST | REQUEST_CLASS | REQUEST_INTERFACE)
+#define REQUEST_HOSTTODEVICE_CLASS_INTERFACE    (REQUEST_HOSTTODEVICE | REQUEST_CLASS | REQUEST_INTERFACE)
+#define REQUEST_DEVICETOHOST_STANDARD_INTERFACE (REQUEST_DEVICETOHOST | REQUEST_STANDARD | REQUEST_INTERFACE)
+
+//	Class requests
+
+#define CDC_SET_LINE_CODING			0x20
+#define CDC_GET_LINE_CODING			0x21
+#define CDC_SET_CONTROL_LINE_STATE	0x22
+#define CDC_SEND_BREAK				0x23
+
+#define MSC_RESET					0xFF
+#define MSC_GET_MAX_LUN				0xFE
+
+//	Descriptors
+
+#define USB_DEVICE_DESC_SIZE 18
+#define USB_CONFIGUARTION_DESC_SIZE 9
+#define USB_INTERFACE_DESC_SIZE 9
+#define USB_ENDPOINT_DESC_SIZE 7
+
+#define USB_DEVICE_DESCRIPTOR_TYPE             1
+#define USB_CONFIGURATION_DESCRIPTOR_TYPE      2
+#define USB_STRING_DESCRIPTOR_TYPE             3
+#define USB_INTERFACE_DESCRIPTOR_TYPE          4
+#define USB_ENDPOINT_DESCRIPTOR_TYPE           5
+
+// usb_20.pdf Table 9.6 Standard Feature Selectors
+#define DEVICE_REMOTE_WAKEUP                   1
+#define ENDPOINT_HALT                          2
+#define TEST_MODE                              3
+
+// usb_20.pdf Figure 9-4. Information Returned by a GetStatus() Request to a Device
+#define FEATURE_SELFPOWERED_ENABLED     (1 << 0)
+#define FEATURE_REMOTE_WAKEUP_ENABLED   (1 << 1)
+
+#define USB_DEVICE_CLASS_COMMUNICATIONS        0x02
+#define USB_DEVICE_CLASS_HUMAN_INTERFACE       0x03
+#define USB_DEVICE_CLASS_STORAGE               0x08
+#define USB_DEVICE_CLASS_VENDOR_SPECIFIC       0xFF
+
+#define USB_CONFIG_POWERED_MASK                0x40
+#define USB_CONFIG_BUS_POWERED                 0x80
+#define USB_CONFIG_SELF_POWERED                0xC0
+#define USB_CONFIG_REMOTE_WAKEUP               0x20
+
+// bMaxPower in Configuration Descriptor
+#define USB_CONFIG_POWER_MA(mA)                ((mA)/2)
+
+// bEndpointAddress in Endpoint Descriptor
+#define USB_ENDPOINT_DIRECTION_MASK            0x80
+#define USB_ENDPOINT_OUT(addr)                 (lowByte((addr) | 0x00))
+#define USB_ENDPOINT_IN(addr)                  (lowByte((addr) | 0x80))
+
+#define USB_ENDPOINT_TYPE_MASK                 0x03
+#define USB_ENDPOINT_TYPE_CONTROL              0x00
+#define USB_ENDPOINT_TYPE_ISOCHRONOUS          0x01
+#define USB_ENDPOINT_TYPE_BULK                 0x02
+#define USB_ENDPOINT_TYPE_INTERRUPT            0x03
+
+#define TOBYTES(x) ((x) & 0xFF),(((x) >> 8) & 0xFF)
+
+#define CDC_V1_10                               0x0110
+#define CDC_COMMUNICATION_INTERFACE_CLASS       0x02
+
+#define CDC_CALL_MANAGEMENT                     0x01
+#define CDC_ABSTRACT_CONTROL_MODEL              0x02
+#define CDC_HEADER                              0x00
+#define CDC_ABSTRACT_CONTROL_MANAGEMENT         0x02
+#define CDC_UNION                               0x06
+#define CDC_CS_INTERFACE                        0x24
+#define CDC_CS_ENDPOINT                         0x25
+#define CDC_DATA_INTERFACE_CLASS                0x0A
+
+#define MSC_SUBCLASS_SCSI						0x06 
+#define MSC_PROTOCOL_BULK_ONLY					0x50 
+
+#ifndef USB_VERSION
+#define USB_VERSION 0x200
+#endif
+
+//	Device
+typedef struct {
+	u8 len;				// 18
+	u8 dtype;			// 1 USB_DEVICE_DESCRIPTOR_TYPE
+	u16 usbVersion;		// 0x200 or 0x210
+	u8	deviceClass;
+	u8	deviceSubClass;
+	u8	deviceProtocol;
+	u8	packetSize0;	// Packet 0
+	u16	idVendor;
+	u16	idProduct;
+	u16	deviceVersion;	// 0x100
+	u8	iManufacturer;
+	u8	iProduct;
+	u8	iSerialNumber;
+	u8	bNumConfigurations;
+} DeviceDescriptor;
+
+//	Config
+typedef struct {
+	u8	len;			// 9
+	u8	dtype;			// 2
+	u16 clen;			// total length
+	u8	numInterfaces;
+	u8	config;
+	u8	iconfig;
+	u8	attributes;
+	u8	maxPower;
+} ConfigDescriptor;
+
+//	String
+
+//	Interface
+typedef struct
+{
+	u8 len;		// 9
+	u8 dtype;	// 4
+	u8 number;
+	u8 alternate;
+	u8 numEndpoints;
+	u8 interfaceClass;
+	u8 interfaceSubClass;
+	u8 protocol;
+	u8 iInterface;
+} InterfaceDescriptor;
+
+//	Endpoint
+typedef struct
+{
+	u8 len;		// 7
+	u8 dtype;	// 5
+	u8 addr;
+	u8 attr;
+	u16 packetSize;
+	u8 interval;
+} EndpointDescriptor;
+
+// Interface Association Descriptor
+// Used to bind 2 interfaces together in CDC compostite device
+typedef struct
+{
+	u8 len;				// 8
+	u8 dtype;			// 11
+	u8 firstInterface;
+	u8 interfaceCount;
+	u8 functionClass;
+	u8 funtionSubClass;
+	u8 functionProtocol;
+	u8 iInterface;
+} IADDescriptor;
+
+//	CDC CS interface descriptor
+typedef struct
+{
+	u8 len;		// 5
+	u8 dtype;	// 0x24
+	u8 subtype;
+	u8 d0;
+	u8 d1;
+} CDCCSInterfaceDescriptor;
+
+typedef struct
+{
+	u8 len;		// 4
+	u8 dtype;	// 0x24
+	u8 subtype;
+	u8 d0;
+} CDCCSInterfaceDescriptor4;
+
+typedef struct 
+{
+    u8	len;
+    u8 	dtype;		// 0x24
+    u8 	subtype;	// 1
+    u8 	bmCapabilities;
+    u8 	bDataInterface;
+} CMFunctionalDescriptor;
+	
+typedef struct 
+{
+    u8	len;
+    u8 	dtype;		// 0x24
+    u8 	subtype;	// 1
+    u8 	bmCapabilities;
+} ACMFunctionalDescriptor;
+
+typedef struct 
+{
+	//	IAD
+	IADDescriptor				iad;	// Only needed on compound device
+
+	//	Control
+	InterfaceDescriptor			cif;	// 
+	CDCCSInterfaceDescriptor	header;
+	CMFunctionalDescriptor		callManagement;			// Call Management
+	ACMFunctionalDescriptor		controlManagement;		// ACM
+	CDCCSInterfaceDescriptor	functionalDescriptor;	// CDC_UNION
+	EndpointDescriptor			cifin;
+
+	//	Data
+	//InterfaceDescriptor			dif; // kai:removed
+	EndpointDescriptor			in;
+	EndpointDescriptor			out;
+} CDCDescriptor;
+
+typedef struct 
+{
+	InterfaceDescriptor			msc;
+	EndpointDescriptor			in;
+	EndpointDescriptor			out;
+} MSCDescriptor;
+
+
+#define D_DEVICE(_class,_subClass,_proto,_packetSize0,_vid,_pid,_version,_im,_ip,_is,_configs) \
+	{ 18, 1, USB_VERSION, _class,_subClass,_proto,_packetSize0,_vid,_pid,_version,_im,_ip,_is,_configs }
+
+#define D_CONFIG(_totalLength,_interfaces) \
+	{ 9, 2, _totalLength,_interfaces, 1, 0, USB_CONFIG_BUS_POWERED | USB_CONFIG_REMOTE_WAKEUP, USB_CONFIG_POWER_MA(500) }
+
+#define D_INTERFACE(_n,_numEndpoints,_class,_subClass,_protocol) \
+	{ 9, 4, _n, 0, _numEndpoints, _class,_subClass, _protocol, 0 }
+
+#define D_ENDPOINT(_addr,_attr,_packetSize, _interval) \
+	{ 7, 5, _addr,_attr,_packetSize, _interval }
+
+#define D_IAD(_firstInterface, _count, _class, _subClass, _protocol) \
+	{ 8, 11, _firstInterface, _count, _class, _subClass, _protocol, 0 }
+
+#define D_CDCCS(_subtype,_d0,_d1)	{ 5, 0x24, _subtype, _d0, _d1 }
+#define D_CDCCS4(_subtype,_d0)		{ 4, 0x24, _subtype, _d0 }
+
+// Bootloader related fields
+// Old Caterina bootloader places the MAGIC key into unsafe RAM locations (it can be rewritten
+// by the running sketch before to actual reboot).
+// Newer bootloaders, recognizable by the LUFA "signature" at the end of the flash, can handle both
+// the usafe and the safe location.
+#ifndef MAGIC_KEY
+#define MAGIC_KEY 0x7777
+#endif
+
+#ifndef MAGIC_KEY_POS
+#define MAGIC_KEY_POS 0x0800
+#endif
+
+#ifndef NEW_LUFA_SIGNATURE
+#define NEW_LUFA_SIGNATURE 0xDCFB
+#endif
+
+#endif

test/arduino_leonardo_bridge_castrated_cdc/arduino_leonardo_bridge_castrated_cdc.ino

@@ -0,0 +1,64 @@
+/*
+  bridge USB-serial to hardware-serial
+
+  for Arduinos based on ATmega32u4 (Leonardo and compatible Pro Micro, Micro)
+  hardware serial is configured with baud-rate, databits, stopbits, parity as send over USB
+
+  see https://github.com/arduino/Arduino/tree/master/hardware/arduino/avr/cores/arduino 
+  -> CDC.cpp|HardwareSerial.cpp for serial implementation details
+
+  this sketch is mainly for demonstration / test of CDC communication
+  performance as real usb-serial bridge would be inacceptable as each byte is send in separate USB packet
+*/
+
+uint32_t baud = 9600;
+uint8_t databits = 8;
+uint8_t stopbits = 1;
+uint8_t parity = 0;
+
+void setup() {
+  Serial.begin(baud); // USB
+  Serial1.begin(baud, SERIAL_8N1);
+}
+
+void loop() {
+  // show USB connected state
+  if (Serial) TXLED1;
+  else        TXLED0;
+
+  // configure hardware serial
+  if (Serial.baud() != baud ||
+      Serial.numbits() != databits ||
+      Serial.stopbits() != stopbits ||
+      Serial.paritytype() != parity) {
+    baud = Serial.baud();
+    databits = Serial.numbits();
+    stopbits = Serial.stopbits();
+    parity = Serial.paritytype();
+    uint8_t config = 0; // ucsrc register
+    switch (databits) {
+      case 5: break;
+      case 6: config |= 2; break;
+      case 7: config |= 4; break;
+      case 8: config |= 6; break;
+      default: config |= 6;
+    }
+    switch (stopbits) {
+      case 2: config |= 8;
+        // 1.5 stopbits not supported
+    }
+    switch (parity) {
+      case 1: config |= 0x30; break; // odd
+      case 2: config |= 0x20; break; // even
+        // mark, space not supported
+    }
+    Serial1.end();
+    Serial1.begin(baud, config);
+  }
+
+  // bridge
+  if (Serial.available() > 0)
+    Serial1.write(Serial.read());
+  if (Serial1.available() > 0)
+    Serial.write(Serial1.read());
+}