Arduino互換Metaboardを紐解く

安くArduinoが欲しい。そんな中でArduinoUNOとか高いし、安上がりでArduinoは手に入らないかと考えていたところ、Metaboardというマイコン一つでArduinoが作れるというのを知る。本来、ArduinoはコアとなるAVRマイコンとそのマイコンにファームウエアを書き込むためのUSB付きマイコンがセットになっているのだが、ここではV-USBベースのUSBaspをブートローダーとして機能し単体でUSBからファームウエアの書き換えが可能なArduinoを制作した。
スペックはATmega328pな20MHzであわよくば、ブートローダをブラッシュアップしようと思ったが逆にコードサイズが大きくなっただけという、どうしてこうなった。

main.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <avr/boot.h>
#include <avr/eeprom.h>
#include <util/delay.h>

#include "usbdrv.c"

/* ------------------------------------------------------------------------ */

/* Request constants used by USBasp */
#define USBASP_FUNC_CONNECT         1
#define USBASP_FUNC_DISCONNECT      2
#define USBASP_FUNC_TRANSMIT        3
#define USBASP_FUNC_READFLASH       4
#define USBASP_FUNC_ENABLEPROG      5
#define USBASP_FUNC_WRITEFLASH      6
#define USBASP_FUNC_READEEPROM      7
#define USBASP_FUNC_WRITEEEPROM     8
#define USBASP_FUNC_SETLONGADDRESS  9

#if (FLASHEND) > 0xffff /* we need long addressing */
#define CURRENT_ADDRESS  currentAddress.l
#define addr_t uint32_t
#else
#define CURRENT_ADDRESS  currentAddress.w[0]
#define addr_t uint16_t
#endif

typedef union longConverter{
	addr_t l;
	uint16_t w[sizeof(addr_t)/2];
	uchar b[sizeof(addr_t)];
} longConverter_t;

static uchar requestBootLoaderExit;
static longConverter_t  currentAddress; /* in bytes */
static uchar bytesRemaining;
static uchar isLastPage;
static uchar currentRequest;

static const uchar signatureBytes[4] = {
#ifdef SIGNATURE_BYTES
	SIGNATURE_BYTES
#elif defined (__AVR_ATmega168__) || defined (__AVR_ATmega168P__)
	0x1e, 0x94, 0x06, 0
#elif defined (__AVR_ATmega328P__)
	0x1e, 0x95, 0x0f, 0
#else
#error "Device signature is not known, please edit main.c!"
#endif
};

/* ------------------------------------------------------------------------ */

uchar   usbFunctionSetup(uchar data[8])
{
	static uchar replyBuffer[4];
	usbRequest_t *rq = (void *)data;
	uchar len = 0;
	usbMsgPtr = replyBuffer;
	
	if(rq->bRequest == USBASP_FUNC_TRANSMIT){   /* emulate parts of ISP protocol */
		{
			uchar rval = 0;
			usbWord_t address;
			
			address.bytes[1] = rq->wValue.bytes[1];
			address.bytes[0] = rq->wIndex.bytes[0];
			if(rq->wValue.bytes[0] == 0x30){        /* read signature */
				rval = rq->wIndex.bytes[0] & 3;
				rval = signatureBytes[rval];
			} else if(rq->wValue.bytes[0] == 0xa0){  /* read EEPROM byte */
				rval = eeprom_read_byte((void *)address.word);
			} else if(rq->wValue.bytes[0] == 0xc0){  /* write EEPROM byte */
				eeprom_write_byte((void *)address.word, rq->wIndex.bytes[1]);
			} else {
				/* ignore all others, return default value == 0 */
			}
			replyBuffer[3] = rval;
			len = 4;
		}
	} else if(rq->bRequest == USBASP_FUNC_ENABLEPROG){
		len = 1;
	} else if(rq->bRequest >= USBASP_FUNC_READFLASH && rq->bRequest <= USBASP_FUNC_SETLONGADDRESS){
		currentAddress.w[0] = rq->wValue.word;
		if(rq->bRequest == USBASP_FUNC_SETLONGADDRESS){
#if (FLASHEND) > 0xffff
			currentAddress.w[1] = rq->wIndex.word;
#endif
		} else {
			bytesRemaining = rq->wLength.bytes[0];
			isLastPage = rq->wIndex.bytes[1] & 0x02;
			currentRequest = rq->bRequest;
			len = 0xff; /* hand over to usbFunctionRead() / usbFunctionWrite() */
		}
	} else if(rq->bRequest == USBASP_FUNC_DISCONNECT){
		requestBootLoaderExit = 1;      /* allow proper shutdown/close of connection */
	} else {
		/* ignore: USBASP_FUNC_CONNECT */
	}
	
	return len;
}

uchar usbFunctionWrite(uchar *data, uchar len)
{
	uchar   isLast;

	if(len > bytesRemaining){
		len = bytesRemaining;
	}
	bytesRemaining -= len;
	if(bytesRemaining == 0){
		isLast = 1;
	}
	if(currentRequest >= USBASP_FUNC_READEEPROM){
		{
			uchar i;
			for(i = 0; i < len; i++){
				eeprom_write_byte((void *)(currentAddress.w[0]++), *data++);
			}
		}
	} else {
		{
			uchar i;
			for(i = 0; i < len;){
				if((currentAddress.w[0] & (SPM_PAGESIZE - 1)) == 0){    /* if page start: erase */
					cli();
					boot_page_erase(CURRENT_ADDRESS);   /* erase page */
					sei();
					boot_spm_busy_wait();               /* wait until page is erased */
				}
				i += 2;
				cli();
				boot_page_fill(CURRENT_ADDRESS, *(uint16_t *)data);
				sei();
				CURRENT_ADDRESS += 2;
				data += 2;
				/* write page when we cross page boundary or we have the last partial page */
				if((currentAddress.w[0] & (SPM_PAGESIZE - 1)) == 0 || (isLast && i >= len && isLastPage)){
					cli();
					boot_page_write(CURRENT_ADDRESS - 2);
					sei();
					boot_spm_busy_wait();
					cli();
					boot_rww_enable();
					sei();
				}
			}
		}
	}
	
	return isLast;
}

uchar usbFunctionRead(uchar *data, uchar len)
{
	if(len > bytesRemaining){
		len = bytesRemaining;
	}
	bytesRemaining -= len;
	{
		uchar   i;
		for(i = 0; i < len; i++){
			if(currentRequest >= USBASP_FUNC_READEEPROM){
				*data = eeprom_read_byte((void *)currentAddress.w[0]);
			} else {
				*data = pgm_read_byte((void *)CURRENT_ADDRESS);
			}
			data++;
			CURRENT_ADDRESS++;
		}
	}

	return len;
}

/* ------------------------------------------------------------------------ */

static void (*nullVector)(void) __attribute__((__noreturn__));

static void __attribute__((__noreturn__)) leaveBootloader()
{
	cli();
	USB_INTR_ENABLE = 0;
	USB_INTR_CFG = 0;     /* also reset config bits */
	MCUCR = (1 << IVCE);  /* enable change of interrupt vectors */
	MCUCR = (0 << IVSEL); /* move interrupts to application flash section */
	/* We must go through a global function pointer variable instead of writing
	*  ((void (*)(void))0)();
	* because the compiler optimizes a constant 0 to "rcall 0" which is not
	* handled correctly by the assembler.
	*/
	nullVector();
}

int __attribute__((noreturn)) main(void)
{
	if(!(MCUSR & (1 << EXTRF))){ /* If this was not an external reset, ignore */
		leaveBootloader();
	}
	wdt_disable();
	MCUSR = 0;            /* clear all reset flags for next time */
	MCUCR = (1 << IVCE);  /* enable change of interrupt vectors */
	MCUCR = (1 << IVSEL); /* move interrupts to boot flash section */
	usbInit();
	usbDeviceDisconnect();
	{
		uchar i = 0;
		while(--i){
			_delay_ms(1);
		}
	}
	usbDeviceConnect();
	sei();
	for(;;) {
		if(requestBootLoaderExit){
			_delay_loop_2(65535);
			break;
		}
		usbPoll();
	}
	usbDeviceDisconnect();
	leaveBootloader();
}

usbconfig.h

/* Name: usbconfig.h
 * Project: V-USB, virtual USB port for Atmel's(r) AVR(r) microcontrollers
 * Author: Christian Starkjohann
 * Creation Date: 2005-04-01
 * Tabsize: 4
 * Copyright: (c) 2005 by OBJECTIVE DEVELOPMENT Software GmbH
 * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
 * This Revision: $Id: usbconfig-prototype.h 785 2010-05-30 17:57:07Z cs $
 */

#ifndef __usbconfig_h_included__
#define __usbconfig_h_included__

/*
General Description:
This file is an example configuration (with inline documentation) for the USB
driver. It configures V-USB for USB D+ connected to Port D bit 2 (which is
also hardware interrupt 0 on many devices) and USB D- to Port D bit 4. You may
wire the lines to any other port, as long as D+ is also wired to INT0 (or any
other hardware interrupt, as long as it is the highest level interrupt, see
section at the end of this file).
+ To create your own usbconfig.h file, copy this file to your project's
+ firmware source directory) and rename it to "usbconfig.h".
+ Then edit it accordingly.
*/

/* ---------------------------- Hardware Config ---------------------------- */

#define USB_CFG_IOPORTNAME      D
/* This is the port where the USB bus is connected. When you configure it to
 * "B", the registers PORTB, PINB and DDRB will be used.
 */
#define USB_CFG_DMINUS_BIT      4
/* This is the bit number in USB_CFG_IOPORT where the USB D- line is connected.
 * This may be any bit in the port.
 */
#define USB_CFG_DPLUS_BIT       2
/* This is the bit number in USB_CFG_IOPORT where the USB D+ line is connected.
 * This may be any bit in the port. Please note that D+ must also be connected
 * to interrupt pin INT0! [You can also use other interrupts, see section
 * "Optional MCU Description" below, or you can connect D- to the interrupt, as
 * it is required if you use the USB_COUNT_SOF feature. If you use D- for the
 * interrupt, the USB interrupt will also be triggered at Start-Of-Frame
 * markers every millisecond.]
 */
#define USB_CFG_CLOCK_KHZ       (F_CPU/1000)
/* Clock rate of the AVR in kHz. Legal values are 12000, 12800, 15000, 16000,
 * 16500, 18000 and 20000. The 12.8 MHz and 16.5 MHz versions of the code
 * require no crystal, they tolerate +/- 1% deviation from the nominal
 * frequency. All other rates require a precision of 2000 ppm and thus a
 * crystal!
 * Since F_CPU should be defined to your actual clock rate anyway, you should
 * not need to modify this setting.
 */
#define USB_CFG_CHECK_CRC       0
/* Define this to 1 if you want that the driver checks integrity of incoming
 * data packets (CRC checks). CRC checks cost quite a bit of code size and are
 * currently only available for 18 MHz crystal clock. You must choose
 * USB_CFG_CLOCK_KHZ = 18000 if you enable this option.
 */

/* ----------------------- Optional Hardware Config ------------------------ */

/* #define USB_CFG_PULLUP_IOPORTNAME   D */
/* If you connect the 1.5k pullup resistor from D- to a port pin instead of
 * V+, you can connect and disconnect the device from firmware by calling
 * the macros usbDeviceConnect() and usbDeviceDisconnect() (see usbdrv.h).
 * This constant defines the port on which the pullup resistor is connected.
 */
/* #define USB_CFG_PULLUP_BIT          4 */
/* This constant defines the bit number in USB_CFG_PULLUP_IOPORT (defined
 * above) where the 1.5k pullup resistor is connected. See description
 * above for details.
 */

/* --------------------------- Functional Range ---------------------------- */

#define USB_CFG_HAVE_INTRIN_ENDPOINT    0
/* Define this to 1 if you want to compile a version with two endpoints: The
 * default control endpoint 0 and an interrupt-in endpoint (any other endpoint
 * number).
 */
#define USB_CFG_HAVE_INTRIN_ENDPOINT3   0
/* Define this to 1 if you want to compile a version with three endpoints: The
 * default control endpoint 0, an interrupt-in endpoint 3 (or the number
 * configured below) and a catch-all default interrupt-in endpoint as above.
 * You must also define USB_CFG_HAVE_INTRIN_ENDPOINT to 1 for this feature.
 */
#define USB_CFG_EP3_NUMBER              3
/* If the so-called endpoint 3 is used, it can now be configured to any other
 * endpoint number (except 0) with this macro. Default if undefined is 3.
 */
/* #define USB_INITIAL_DATATOKEN           USBPID_DATA1 */
/* The above macro defines the startup condition for data toggling on the
 * interrupt/bulk endpoints 1 and 3. Defaults to USBPID_DATA1.
 * Since the token is toggled BEFORE sending any data, the first packet is
 * sent with the oposite value of this configuration!
 */
#define USB_CFG_IMPLEMENT_HALT          0
/* Define this to 1 if you also want to implement the ENDPOINT_HALT feature
 * for endpoint 1 (interrupt endpoint). Although you may not need this feature,
 * it is required by the standard. We have made it a config option because it
 * bloats the code considerably.
 */
#define USB_CFG_SUPPRESS_INTR_CODE      0
/* Define this to 1 if you want to declare interrupt-in endpoints, but don't
 * want to send any data over them. If this macro is defined to 1, functions
 * usbSetInterrupt() and usbSetInterrupt3() are omitted. This is useful if
 * you need the interrupt-in endpoints in order to comply to an interface
 * (e.g. HID), but never want to send any data. This option saves a couple
 * of bytes in flash memory and the transmit buffers in RAM.
 */
#define USB_CFG_INTR_POLL_INTERVAL      10
/* If you compile a version with endpoint 1 (interrupt-in), this is the poll
 * interval. The value is in milliseconds and must not be less than 10 ms for
 * low speed devices.
 */
#define USB_CFG_IS_SELF_POWERED         0
/* Define this to 1 if the device has its own power supply. Set it to 0 if the
 * device is powered from the USB bus.
 */
#define USB_CFG_MAX_BUS_POWER           100
/* Set this variable to the maximum USB bus power consumption of your device.
 * The value is in milliamperes. [It will be divided by two since USB
 * communicates power requirements in units of 2 mA.]
 */
#define USB_CFG_IMPLEMENT_FN_WRITE      1
/* Set this to 1 if you want usbFunctionWrite() to be called for control-out
 * transfers. Set it to 0 if you don't need it and want to save a couple of
 * bytes.
 */
#define USB_CFG_IMPLEMENT_FN_READ       1
/* Set this to 1 if you need to send control replies which are generated
 * "on the fly" when usbFunctionRead() is called. If you only want to send
 * data from a static buffer, set it to 0 and return the data from
 * usbFunctionSetup(). This saves a couple of bytes.
 */
#define USB_CFG_IMPLEMENT_FN_WRITEOUT   0
/* Define this to 1 if you want to use interrupt-out (or bulk out) endpoints.
 * You must implement the function usbFunctionWriteOut() which receives all
 * interrupt/bulk data sent to any endpoint other than 0. The endpoint number
 * can be found in 'usbRxToken'.
 */
#define USB_CFG_HAVE_FLOWCONTROL        0
/* Define this to 1 if you want flowcontrol over USB data. See the definition
 * of the macros usbDisableAllRequests() and usbEnableAllRequests() in
 * usbdrv.h.
 */
#define USB_CFG_DRIVER_FLASH_PAGE       0
/* If the device has more than 64 kBytes of flash, define this to the 64 k page
 * where the driver's constants (descriptors) are located. Or in other words:
 * Define this to 1 for boot loaders on the ATMega128.
 */
#define USB_CFG_LONG_TRANSFERS          0
/* Define this to 1 if you want to send/receive blocks of more than 254 bytes
 * in a single control-in or control-out transfer. Note that the capability
 * for long transfers increases the driver size.
 */
/* #define USB_RX_USER_HOOK(data, len)     if(usbRxToken == (uchar)USBPID_SETUP) blinkLED(); */
/* This macro is a hook if you want to do unconventional things. If it is
 * defined, it's inserted at the beginning of received message processing.
 * If you eat the received message and don't want default processing to
 * proceed, do a return after doing your things. One possible application
 * (besides debugging) is to flash a status LED on each packet.
 */
/* #define USB_RESET_HOOK(resetStarts)     if(!resetStarts){hadUsbReset();} */
/* This macro is a hook if you need to know when an USB RESET occurs. It has
 * one parameter which distinguishes between the start of RESET state and its
 * end.
 */
/* #define USB_SET_ADDRESS_HOOK()              hadAddressAssigned(); */
/* This macro (if defined) is executed when a USB SET_ADDRESS request was
 * received.
 */
#define USB_COUNT_SOF                   0
/* define this macro to 1 if you need the global variable "usbSofCount" which
 * counts SOF packets. This feature requires that the hardware interrupt is
 * connected to D- instead of D+.
 */
/* #ifdef __ASSEMBLER__
 * macro myAssemblerMacro
 *     in      YL, TCNT0
 *     sts     timer0Snapshot, YL
 *     endm
 * #endif
 * #define USB_SOF_HOOK                    myAssemblerMacro
 * This macro (if defined) is executed in the assembler module when a
 * Start Of Frame condition is detected. It is recommended to define it to
 * the name of an assembler macro which is defined here as well so that more
 * than one assembler instruction can be used. The macro may use the register
 * YL and modify SREG. If it lasts longer than a couple of cycles, USB messages
 * immediately after an SOF pulse may be lost and must be retried by the host.
 * What can you do with this hook? Since the SOF signal occurs exactly every
 * 1 ms (unless the host is in sleep mode), you can use it to tune OSCCAL in
 * designs running on the internal RC oscillator.
 * Please note that Start Of Frame detection works only if D- is wired to the
 * interrupt, not D+. THIS IS DIFFERENT THAN MOST EXAMPLES!
 */
#define USB_CFG_CHECK_DATA_TOGGLING     0
/* define this macro to 1 if you want to filter out duplicate data packets
 * sent by the host. Duplicates occur only as a consequence of communication
 * errors, when the host does not receive an ACK. Please note that you need to
 * implement the filtering yourself in usbFunctionWriteOut() and
 * usbFunctionWrite(). Use the global usbCurrentDataToken and a static variable
 * for each control- and out-endpoint to check for duplicate packets.
 */
#define USB_CFG_HAVE_MEASURE_FRAME_LENGTH   0
/* define this macro to 1 if you want the function usbMeasureFrameLength()
 * compiled in. This function can be used to calibrate the AVR's RC oscillator.
 */
#define USB_USE_FAST_CRC                0
/* The assembler module has two implementations for the CRC algorithm. One is
 * faster, the other is smaller. This CRC routine is only used for transmitted
 * messages where timing is not critical. The faster routine needs 31 cycles
 * per byte while the smaller one needs 61 to 69 cycles. The faster routine
 * may be worth the 32 bytes bigger code size if you transmit lots of data and
 * run the AVR close to its limit.
 */

/* -------------------------- Device Description --------------------------- */

#define  USB_CFG_VENDOR_ID       0xc0, 0x16 /* = 0x16c0 = 5824 = voti.nl */
/* USB vendor ID for the device, low byte first. If you have registered your
 * own Vendor ID, define it here. Otherwise you may use one of obdev's free
 * shared VID/PID pairs. Be sure to read USB-IDs-for-free.txt for rules!
 * *** IMPORTANT NOTE ***
 * This template uses obdev's shared VID/PID pair for Vendor Class devices
 * with libusb: 0x16c0/0x5dc.  Use this VID/PID pair ONLY if you understand
 * the implications!
 */
#define  USB_CFG_DEVICE_ID       0xdc, 0x05 /* = 0x05dc = 1500 */
/* This is the ID of the product, low byte first. It is interpreted in the
 * scope of the vendor ID. If you have registered your own VID with usb.org
 * or if you have licensed a PID from somebody else, define it here. Otherwise
 * you may use one of obdev's free shared VID/PID pairs. See the file
 * USB-IDs-for-free.txt for details!
 * *** IMPORTANT NOTE ***
 * This template uses obdev's shared VID/PID pair for Vendor Class devices
 * with libusb: 0x16c0/0x5dc.  Use this VID/PID pair ONLY if you understand
 * the implications!
 */
#define USB_CFG_DEVICE_VERSION  0x02, 0x01
/* Version number of the device: Minor number first, then major number.
 */
#define USB_CFG_VENDOR_NAME 'w','w','w','.','f','i','s','c','h','l','.','d','e'
#define USB_CFG_VENDOR_NAME_LEN 13
/* These two values define the vendor name returned by the USB device. The name
 * must be given as a list of characters under single quotes. The characters
 * are interpreted as Unicode (UTF-16) entities.
 * If you don't want a vendor name string, undefine these macros.
 * ALWAYS define a vendor name containing your Internet domain name if you use
 * obdev's free shared VID/PID pair. See the file USB-IDs-for-free.txt for
 * details.
 */
#define USB_CFG_DEVICE_NAME 'U', 'S', 'B', 'a', 's', 'p'
#define USB_CFG_DEVICE_NAME_LEN 6
/* Same as above for the device name. If you don't want a device name, undefine
 * the macros. See the file USB-IDs-for-free.txt before you assign a name if
 * you use a shared VID/PID.
 */
/*#define USB_CFG_SERIAL_NUMBER   'N', 'o', 'n', 'e' */
/*#define USB_CFG_SERIAL_NUMBER_LEN   0 */
/* Same as above for the serial number. If you don't want a serial number,
 * undefine the macros.
 * It may be useful to provide the serial number through other means than at
 * compile time. See the section about descriptor properties below for how
 * to fine tune control over USB descriptors such as the string descriptor
 * for the serial number.
 */
#define USB_CFG_DEVICE_CLASS        0    /* set to 0 if deferred to interface */
#define USB_CFG_DEVICE_SUBCLASS     0
/* See USB specification if you want to conform to an existing device class.
 * Class 0xff is "vendor specific".
 */
#define USB_CFG_INTERFACE_CLASS     0   /* define class here if not at device level */
#define USB_CFG_INTERFACE_SUBCLASS  0
#define USB_CFG_INTERFACE_PROTOCOL  0
/* See USB specification if you want to conform to an existing device class or
 * protocol. The following classes must be set at interface level:
 * HID class is 3, no subclass and protocol required (but may be useful!)
 * CDC class is 2, use subclass 2 and protocol 1 for ACM
 */
/* #define USB_CFG_HID_REPORT_DESCRIPTOR_LENGTH    42 */
/* Define this to the length of the HID report descriptor, if you implement
 * an HID device. Otherwise don't define it or define it to 0.
 * If you use this define, you must add a PROGMEM character array named
 * "usbHidReportDescriptor" to your code which contains the report descriptor.
 * Don't forget to keep the array and this define in sync!
 */

/* #define USB_PUBLIC static */
/* Use the define above if you #include usbdrv.c instead of linking against it.
 * This technique saves a couple of bytes in flash memory.
 */

/* ------------------- Fine Control over USB Descriptors ------------------- */
/* If you don't want to use the driver's default USB descriptors, you can
 * provide our own. These can be provided as (1) fixed length static data in
 * flash memory, (2) fixed length static data in RAM or (3) dynamically at
 * runtime in the function usbFunctionDescriptor(). See usbdrv.h for more
 * information about this function.
 * Descriptor handling is configured through the descriptor's properties. If
 * no properties are defined or if they are 0, the default descriptor is used.
 * Possible properties are:
 *   + USB_PROP_IS_DYNAMIC: The data for the descriptor should be fetched
 *     at runtime via usbFunctionDescriptor(). If the usbMsgPtr mechanism is
 *     used, the data is in FLASH by default. Add property USB_PROP_IS_RAM if
 *     you want RAM pointers.
 *   + USB_PROP_IS_RAM: The data returned by usbFunctionDescriptor() or found
 *     in static memory is in RAM, not in flash memory.
 *   + USB_PROP_LENGTH(len): If the data is in static memory (RAM or flash),
 *     the driver must know the descriptor's length. The descriptor itself is
 *     found at the address of a well known identifier (see below).
 * List of static descriptor names (must be declared PROGMEM if in flash):
 *   char usbDescriptorDevice[];
 *   char usbDescriptorConfiguration[];
 *   char usbDescriptorHidReport[];
 *   char usbDescriptorString0[];
 *   int usbDescriptorStringVendor[];
 *   int usbDescriptorStringDevice[];
 *   int usbDescriptorStringSerialNumber[];
 * Other descriptors can't be provided statically, they must be provided
 * dynamically at runtime.
 *
 * Descriptor properties are or-ed or added together, e.g.:
 * #define USB_CFG_DESCR_PROPS_DEVICE   (USB_PROP_IS_RAM | USB_PROP_LENGTH(18))
 *
 * The following descriptors are defined:
 *   USB_CFG_DESCR_PROPS_DEVICE
 *   USB_CFG_DESCR_PROPS_CONFIGURATION
 *   USB_CFG_DESCR_PROPS_STRINGS
 *   USB_CFG_DESCR_PROPS_STRING_0
 *   USB_CFG_DESCR_PROPS_STRING_VENDOR
 *   USB_CFG_DESCR_PROPS_STRING_PRODUCT
 *   USB_CFG_DESCR_PROPS_STRING_SERIAL_NUMBER
 *   USB_CFG_DESCR_PROPS_HID
 *   USB_CFG_DESCR_PROPS_HID_REPORT
 *   USB_CFG_DESCR_PROPS_UNKNOWN (for all descriptors not handled by the driver)
 *
 * Note about string descriptors: String descriptors are not just strings, they
 * are Unicode strings prefixed with a 2 byte header. Example:
 * int  serialNumberDescriptor[] = {
 *     USB_STRING_DESCRIPTOR_HEADER(6),
 *     'S', 'e', 'r', 'i', 'a', 'l'
 * };
 */

#define USB_CFG_DESCR_PROPS_DEVICE                  0
#define USB_CFG_DESCR_PROPS_CONFIGURATION           0
#define USB_CFG_DESCR_PROPS_STRINGS                 0
#define USB_CFG_DESCR_PROPS_STRING_0                0
#define USB_CFG_DESCR_PROPS_STRING_VENDOR           0
#define USB_CFG_DESCR_PROPS_STRING_PRODUCT          0
#define USB_CFG_DESCR_PROPS_STRING_SERIAL_NUMBER    0
#define USB_CFG_DESCR_PROPS_HID                     0
#define USB_CFG_DESCR_PROPS_HID_REPORT              0
#define USB_CFG_DESCR_PROPS_UNKNOWN                 0

/* ----------------------- Optional MCU Description ------------------------ */

/* The following configurations have working defaults in usbdrv.h. You
 * usually don't need to set them explicitly. Only if you want to run
 * the driver on a device which is not yet supported or with a compiler
 * which is not fully supported (such as IAR C) or if you use a differnt
 * interrupt than INT0, you may have to define some of these.
 */
/* #define USB_INTR_CFG            MCUCR */
/* #define USB_INTR_CFG_SET        ((1 << ISC00) | (1 << ISC01)) */
/* #define USB_INTR_CFG_CLR        0 */
/* #define USB_INTR_ENABLE         GIMSK */
/* #define USB_INTR_ENABLE_BIT     INT0 */
/* #define USB_INTR_PENDING        GIFR */
/* #define USB_INTR_PENDING_BIT    INTF0 */
/* #define USB_INTR_VECTOR         INT0_vect */

#endif /* __usbconfig_h_included__ */

回路図


信号線とマイコンのポート接続に68Ωが使われているが、ちょっと低すぎ?V-USBじゃなくAVRUSBの名称だった時代は75Ωだった気がするのだが…。D-プルアップ用の抵抗も2.2kΩから1.5kΩに変更されている。あと、耐圧3.6Vのダイオードが使われているが、オシロでみると絶対定格の4Vを適切にクリップせずにオーバーしてしまうケースがみられる。3Vでもいいかもしれない。
AVR側のポートの閾値が5V動作の時2.5Vなのでそれを下回らない程度で十分で直流で3.3Vを超えるとUSB側の保護機能が働き動作しない場合がある。とくにダイオードを省いた構成のMetaboardをみかけるが、USBポートを痛めたくなければダイオードは必須であると思われる。
また上記のファームウエアにおいてはブートローダーを無効化設定するジャンパピンの構成を省いてある。

ソフトウエア

USBasp - USB programmer for Atmel AVR controllers - fischl.de
以上からドライバがダウンロードできます。hidaspxはAvrdudeなどの海外製書き込みソフトが対応してないですが、USBaspは対応しているので(プロジェクト的な)メンテナンスや対応ハードウエアの面で安心です。

Arduino Sketchの設定

Processing/スケッチのディレクトリ/フォルダにある。hardware/boards.txtに下記を加えます。

##############################################################
metaboard.name=Metaboard
metaboard.upload.protocol=usbasp
metaboard.upload.maximum_size=14336
metaboard.upload.speed=19200
metaboard.build.mcu=atmega328p
metaboard.build.f_cpu=20000000L
metaboard.build.core=arduino
metaboard.upload.disable_flushing=true
##############################################################

使い方

ArduinoとMetaboardの大きな違いは書き込み時にリセットボタンを要するということとArduinoはSerial用のポート2つが占有されていますが、Metaboardは外部割り込みポート1つが占有されています。シリアルコンソールを用いたデバックに慣れてると書きこむたびにリセットボタンを押さないといけなかったり、そもそもシリアルコンソールがなかったりしますが、Processing/スケッチが使えることと安上がりという点は十分な利点ですよね。