optiboot.c

#define FUNC_READ 1
#define FUNC_WRITE 1
/**********************************************************/
/* Optiboot bootloader for Arduino                        */
/*                                                        */
/* http://optiboot.googlecode.com                         */
/*                                                        */
/* Arduino-maintained version : See README.TXT            */
/* http://code.google.com/p/arduino/                      */
/*  It is the intent that changes not relevant to the     */
/*  Arduino production envionment get moved from the      */
/*  optiboot project to the arduino project in "lumps."   */
/*                                                        */
/* Heavily optimised bootloader that is faster and        */
/* smaller than the Arduino standard bootloader           */
/*                                                        */
/* Enhancements:                                          */
/*   Fits in 512 bytes, saving 1.5K of code space         */
/*   Higher baud rate speeds up programming               */
/*   Written almost entirely in C                         */
/*   Customisable timeout with accurate timeconstant      */
/*   Optional virtual UART. No hardware UART required.    */
/*   Optional virtual boot partition for devices without. */
/*                                                        */
/* What you lose:                                         */
/*   Implements a skeleton STK500 protocol which is       */
/*     missing several features including EEPROM          */
/*     programming and non-page-aligned writes            */
/*   High baud rate breaks compatibility with standard    */
/*     Arduino flash settings                             */
/*                                                        */
/* Fully supported:                                       */
/*   ATmega168 based devices  (Diecimila etc)             */
/*   ATmega328P based devices (Duemilanove etc)           */
/*                                                        */
/* Beta test (believed working.)                          */
/*   ATmega8 based devices (Arduino legacy)               */
/*   ATmega328 non-picopower devices                      */
/*   ATmega644P based devices (Sanguino)                  */
/*   ATmega1284P based devices                            */
/*   ATmega1280 based devices (Arduino Mega)              */
/*                                                        */
/* Alpha test                                             */
/*   ATmega32                                             */
/*                                                        */
/* Work in progress:                                      */
/*   ATtiny84 based devices (Luminet)                     */
/*                                                        */
/* Does not support:                                      */
/*   USB based devices (eg. Teensy, Leonardo)             */
/*                                                        */
/* Assumptions:                                           */
/*   The code makes several assumptions that reduce the   */
/*   code size. They are all true after a hardware reset, */
/*   but may not be true if the bootloader is called by   */
/*   other means or on other hardware.                    */
/*     No interrupts can occur                            */
/*     UART and Timer 1 are set to their reset state      */
/*     SP points to RAMEND                                */
/*                                                        */
/* Code builds on code, libraries and optimisations from: */
/*   stk500boot.c          by Jason P. Kyle               */
/*   Arduino bootloader    http://arduino.cc              */
/*   Spiff's 1K bootloader http://spiffie.org/know/arduino_1k_bootloader/bootloader.shtml */
/*   avr-libc project      http://nongnu.org/avr-libc     */
/*   Adaboot               http://www.ladyada.net/library/arduino/bootloader.html */
/*   AVR305                Atmel Application Note         */
/*                                                        */

/* Copyright 2013-2015 by Bill Westfield.                 */
/* Copyright 2010 by Peter Knight.                        */
/*                                                        */
/* This program is free software; you can redistribute it */
/* and/or modify it under the terms of the GNU General    */
/* Public License as published by the Free Software       */
/* Foundation; either version 2 of the License, or        */
/* (at your option) any later version.                    */
/*                                                        */
/* This program is distributed in the hope that it will   */
/* be useful, but WITHOUT ANY WARRANTY; without even the  */
/* implied warranty of MERCHANTABILITY or FITNESS FOR A   */
/* PARTICULAR PURPOSE.  See the GNU General Public        */
/* License for more details.                              */
/*                                                        */
/* You should have received a copy of the GNU General     */
/* Public License along with this program; if not, write  */
/* to the Free Software Foundation, Inc.,                 */
/* 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA */
/*                                                        */
/* Licence can be viewed at                               */
/* http://www.fsf.org/licenses/gpl.txt                    */
/*                                                        */
/**********************************************************/


/**********************************************************/
/*                                                        */
/* Optional defines:                                      */
/*                                                        */
/**********************************************************/
/*                                                        */
/* BIGBOOT:                                               */
/* Build a 1k bootloader, not 512 bytes. This turns on    */
/* extra functionality.                                   */
/*                                                        */
/* BAUD_RATE:                                             */
/* Set bootloader baud rate.                              */
/*                                                        */
/* SOFT_UART:                                             */
/* Use AVR305 soft-UART instead of hardware UART.         */
/*                                                        */
/* LED_START_FLASHES:                                     */
/* Number of LED flashes on bootup.                       */
/*                                                        */
/* LED_DATA_FLASH:                                        */
/* Flash LED when transferring data. For boards without   */
/* TX or RX LEDs, or for people who like blinky lights.   */
/*                                                        */
/* SUPPORT_EEPROM:                                        */
/* Support reading and writing from EEPROM. This is not   */
/* used by Arduino, so off by default.                    */
/*                                                        */
/* TIMEOUT_MS:                                            */
/* Bootloader timeout period, in milliseconds.            */
/* 500,1000,2000,4000,8000 supported.                     */
/*                                                        */
/* UART:                                                  */
/* UART number (0..n) for devices with more than          */
/* one hardware uart (644P, 1284P, etc)                   */
/*                                                        */
/**********************************************************/

/**********************************************************/
/* Version Numbers!                                       */
/*                                                        */
/* Arduino Optiboot now includes this Version number in   */
/* the source and object code.                            */
/*                                                        */
/* Version 3 was released as zip from the optiboot        */
/*  repository and was distributed with Arduino 0022.     */
/* Version 4 starts with the arduino repository commit    */
/*  that brought the arduino repository up-to-date with   */
/*  the optiboot source tree changes since v3.            */
/* Version 5 was created at the time of the new Makefile  */
/*  structure (Mar, 2013), even though no binaries changed*/
/* It would be good if versions implemented outside the   */
/*  official repository used an out-of-seqeunce version   */
/*  number (like 104.6 if based on based on 4.5) to       */
/*  prevent collisions.                                   */
/*                                                        */
/**********************************************************/

/**********************************************************/
/* Edit History:					  					  */
/*							  							  */
/* Aug 2014						  						  */
/* 6.2 WestfW: make size of length variables dependent    */
/*              on the SPM_PAGESIZE.  This saves space    */
/*              on the chips where it's most important.   */
/* 6.1 WestfW: Fix OPTIBOOT_CUSTOMVER (send it!)	  	  */
/*             Make no-wait mod less picky about	  	  */
/*               skipping the bootloader.		  		  */
/*             Remove some dead code			  		  */
/* Jun 2014						  						  */
/* 6.0 WestfW: Modularize memory read/write functions	  */
/*             Remove serial/flash overlap		  		  */
/*              (and all references to NRWWSTART/etc)	  */
/*             Correctly handle pagesize > 255bytes       */
/*             Add EEPROM support in BIGBOOT (1284)       */
/*             EEPROM write on small chips now causes err */
/*             Split Makefile into smaller pieces         */
/*             Add Wicked devices Wildfire		  		  */
/*	       Move UART=n conditionals into pin_defs.h   	  */
/*	       Remove LUDICOUS_SPEED option		  			  */
/*	       Replace inline assembler for .version      	  */
/*              and add OPTIBOOT_CUSTOMVER for user code  */
/*             Fix LED value for Bobuino (Makefile)       */
/*             Make all functions explicitly inline or    */
/*              noinline, so we fit when using gcc4.8     */
/*             Change optimization options for gcc4.8	  */
/*             Make ENV=arduino work in 1.5.x trees.	  */
/* May 2014                                               */
/* 5.0 WestfW: Add support for 1Mbps UART                 */
/* Mar 2013                                               */
/* 5.0 WestfW: Major Makefile restructuring.              */
/*             See Makefile and pin_defs.h                */
/*             (no binary changes)                        */
/*                                                        */
/* 4.6 WestfW/Pito: Add ATmega32 support                  */
/* 4.6 WestfW/radoni: Don't set LED_PIN as an output if   */
/*                    not used. (LED_START_FLASHES = 0)   */
/* Jan 2013						  */
/* 4.6 WestfW/dkinzer: use autoincrement lpm for read     */
/* 4.6 WestfW/dkinzer: pass reset cause to app in R2      */
/* Mar 2012                                               */
/* 4.5 WestfW: add infrastructure for non-zero UARTS.     */
/* 4.5 WestfW: fix SIGNATURE_2 for m644 (bad in avr-libc) */
/* Jan 2012:                                              */
/* 4.5 WestfW: fix NRWW value for m1284.                  */
/* 4.4 WestfW: use attribute OS_main instead of naked for */
/*             main().  This allows optimizations that we */
/*             count on, which are prohibited in naked    */
/*             functions due to PR42240.  (keeps us less  */
/*             than 512 bytes when compiler is gcc4.5     */
/*             (code from 4.3.2 remains the same.)        */
/* 4.4 WestfW and Maniacbug:  Add m1284 support.  This    */
/*             does not change the 328 binary, so the     */
/*             version number didn't change either. (?)   */
/* June 2011:                                             */
/* 4.4 WestfW: remove automatic soft_uart detect (didn't  */
/*             know what it was doing or why.)  Added a   */
/*             check of the calculated BRG value instead. */
/*             Version stays 4.4; existing binaries are   */
/*             not changed.                               */
/* 4.4 WestfW: add initialization of address to keep      */
/*             the compiler happy.  Change SC'ed targets. */
/*             Return the SW version via READ PARAM       */
/* 4.3 WestfW: catch framing errors in getch(), so that   */
/*             AVRISP works without HW kludges.           */
/*  http://code.google.com/p/arduino/issues/detail?id=368n*/
/* 4.2 WestfW: reduce code size, fix timeouts, change     */
/*             verifySpace to use WDT instead of appstart */
/* 4.1 WestfW: put version number in binary.		  	  */
/**********************************************************/

#define OPTIBOOT_MAJVER 6
#define OPTIBOOT_MINVER 2

/*
 * OPTIBOOT_CUSTOMVER should be defined (by the makefile) for custom edits
 * of optiboot.  That way you don't wind up with very different code that
 * matches the version number of a "released" optiboot.
 */

#if !defined(OPTIBOOT_CUSTOMVER)
#define OPTIBOOT_CUSTOMVER 0
#endif

unsigned const int __attribute__((section(".version"))) 
optiboot_version = 256*(OPTIBOOT_MAJVER + OPTIBOOT_CUSTOMVER) + OPTIBOOT_MINVER;

#include <inttypes.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <avr/eeprom.h>

/*
 * Note that we use our own version of "boot.h"
 * <avr/boot.h> uses sts instructions, but this version uses out instructions
 * This saves cycles and program memory.  Sorry for the name overlap.
 */
#include "boot.h"
#include "uart.h"
#include "watchdog.h"

// We don't use <avr/wdt.h> as those routines have interrupt overhead we don't need.

/*
 * pin_defs.h
 * This contains most of the rather ugly defines that implement our
 * ability to use UART=n and LED=D3, and some avr family bit name differences.
 */
#include "pin_defs.h"

/*
 * stk500.h contains the constant definitions for the stk500v1 comm protocol
 */
#include "optiboot_stk500.h"

#ifndef LED_START_FLASHES
#define LED_START_FLASHES 0
#endif

/*
 * We can never load flash with more than 1 page at a time, so we can save
 * some code space on parts with smaller pagesize by using a smaller int.
 */
#if SPM_PAGESIZE > 255
typedef uint16_t pagelen_t ;
#define GETLENGTH(len) len = getch()<<8; len |= getch()
#else
typedef uint8_t pagelen_t;
#define GETLENGTH(len) (void) getch() /* skip high byte */; len = getch()
#endif


/* Function Prototypes
 * The main() function is in init9, which removes the interrupt vector table
 * we don't need. It is also 'OS_main', which means the compiler does not
 * generate any entry or exit code itself (but unlike 'naked', it doesn't
 * supress some compile-time options we want.)
 */


void __attribute__((noinline)) verifySpace();
void __attribute__((noinline)) watchdogConfig(uint8_t x);


static inline void getNch(uint8_t);
void getNch(uint8_t count) {
  do getch(); while (--count);
  verifySpace();
}

#if LED_START_FLASHES > 0
static inline void flash_led(uint8_t);
#endif
static inline void writebuffer(int8_t memtype, uint8_t *mybuff,
			       uint16_t address, pagelen_t len);
static inline void read_mem(uint8_t memtype,
			    uint16_t address, pagelen_t len);


/*
 * RAMSTART should be self-explanatory.  It's bigger on parts with a
 * lot of peripheral registers.  Let 0x100 be the default
 * Note that RAMSTART (for optiboot) need not be exactly at the start of RAM.
 */
#if !defined(RAMSTART)  // newer versions of gcc avr-libc define RAMSTART
#define RAMSTART 0x100
#if defined (__AVR_ATmega644P__)
// correct for a bug in avr-libc
#undef SIGNATURE_2
#define SIGNATURE_2 0x0A
#elif defined(__AVR_ATmega1280__)
#undef RAMSTART
#define RAMSTART (0x200)
#endif
#endif

/* C zero initialises all global variables. However, that requires */
/* These definitions are NOT zero initialised, but that doesn't matter */
/* This allows us to drop the zero init code, saving us memory */
#define buff    ((uint8_t*)(RAMSTART))

/* Virtual boot partition support */
#ifdef VIRTUAL_BOOT_PARTITION
#define rstVect0_sav (*(uint8_t*)(RAMSTART+SPM_PAGESIZE*2+4))
#define rstVect1_sav (*(uint8_t*)(RAMSTART+SPM_PAGESIZE*2+5))
#define saveVect0_sav (*(uint8_t*)(RAMSTART+SPM_PAGESIZE*2+6))
#define saveVect1_sav (*(uint8_t*)(RAMSTART+SPM_PAGESIZE*2+7))
// Vector to save original reset jump:
//   SPM Ready is least probably used, so it's default
//   if not, use old way WDT_vect_num,
//   or simply set custom save_vect_num in Makefile using vector name
//   or even raw number.
#if !defined (save_vect_num)
#if defined (SPM_RDY_vect_num)
#define save_vect_num (SPM_RDY_vect_num)
#elif defined (SPM_READY_vect_num)
#define save_vect_num (SPM_READY_vect_num)
#elif defined (WDT_vect_num)
#define save_vect_num (WDT_vect_num)
#else
#error Cant find SPM or WDT interrupt vector for this CPU
#endif
#endif //save_vect_num
// check if it's on the same page (code assumes that)
#if (SPM_PAGESIZE <= save_vect_num)
#error Save vector not in the same page as reset!
#endif
#if FLASHEND > 8192
// AVRs with more than 8k of flash have 4-byte vectors, and use jmp.
//  We save only 16 bits of address, so devices with more than 128KB
//  may behave wrong for upper part of address space.
#define rstVect0 2
#define rstVect1 3
#define saveVect0 (save_vect_num*4+2)
#define saveVect1 (save_vect_num*4+3)
#define appstart_vec (save_vect_num*2)
#else
// AVRs with up to 8k of flash have 2-byte vectors, and use rjmp.
#define rstVect0 0
#define rstVect1 1
#define saveVect0 (save_vect_num*2)
#define saveVect1 (save_vect_num*2+1)
#define appstart_vec (save_vect_num)
#endif
#else
#define appstart_vec (0)
#endif // VIRTUAL_BOOT_PARTITION


/* main program starts here */
int optiboot(void) {
  uint8_t ch;

  /*
   * Making these local and in registers prevents the need for initializing
   * them, and also saves space because code no longer stores to memory.
   * (initializing address keeps the compiler happy, but isn't really
   *  necessary, and uses 4 bytes of flash.)
   */
  register uint16_t address = 0;
  register pagelen_t length;

  /* Forever loop: exits by causing WDT reset */
  for (;;) {
    /* get character from UART */
    ch = getch();

    if(ch == STK_GET_PARAMETER) {
      unsigned char which = getch();
      verifySpace();
      /*
       * Send optiboot version as "SW version"
       * Note that the references to memory are optimized away.
       */
      if (which == STK_SW_MINOR) {
	  putch(optiboot_version & 0xFF);
      } else if (which == STK_SW_MAJOR) {
	  putch(optiboot_version >> 8);
      } else {
	/*
	 * GET PARAMETER returns a generic 0x03 reply for
         * other parameters - enough to keep Avrdude happy
	 */
		putch(0x03);
      }
    }
    else if(ch == STK_SET_DEVICE) {
      // SET DEVICE is ignored
      getNch(20);
    }
    else if(ch == STK_SET_DEVICE_EXT) {
      // SET DEVICE EXT is ignored
      getNch(5);
    }
    else if(ch == STK_LOAD_ADDRESS) {
      // LOAD ADDRESS
      uint16_t newAddress;
      newAddress = getch();
      newAddress = (newAddress & 0xff) | (getch() << 8);
#ifdef RAMPZ
      // Transfer top bit to RAMPZ
      RAMPZ = (newAddress & 0x8000) ? 1 : 0;
#endif
      newAddress += newAddress; // Convert from word address to byte address
      address = newAddress;
      verifySpace();
    }
    else if(ch == STK_UNIVERSAL) {
      // UNIVERSAL command is ignored
      getNch(4);
      putch(0x00);
    }
    /* Write memory, length is big endian and is in bytes */
    else if(ch == STK_PROG_PAGE) {
      // PROGRAM PAGE - we support flash programming only, not EEPROM
      uint8_t desttype;
      uint8_t *bufPtr;
      pagelen_t savelength;

      GETLENGTH(length);
      savelength = length;
      desttype = getch();

      // read a page worth of contents
      bufPtr = buff;
      do *bufPtr++ = getch();
      while (--length);

      // Read command terminator, start reply
      verifySpace();

#ifdef VIRTUAL_BOOT_PARTITION
#if FLASHEND > 8192
/*
 * AVR with 4-byte ISR Vectors and "jmp"
 * WARNING: this works only up to 128KB flash!
 */
      if (address == 0) {
	// This is the reset vector page. We need to live-patch the
	// code so the bootloader runs first.
	//
	// Save jmp targets (for "Verify")
	rstVect0_sav = buff[rstVect0];
	rstVect1_sav = buff[rstVect1];
	saveVect0_sav = buff[saveVect0];
	saveVect1_sav = buff[saveVect1];

        // Move RESET jmp target to 'save' vector
        buff[saveVect0] = rstVect0_sav;
        buff[saveVect1] = rstVect1_sav;

        // Add jump to bootloader at RESET vector
        // WARNING: this works as long as 'main' is in first section
        buff[rstVect0] = ((uint16_t)main) & 0xFF;
        buff[rstVect1] = ((uint16_t)main) >> 8;
      }

#else
/*
 * AVR with 2-byte ISR Vectors and rjmp
 */
      if ((uint16_t)(void*)address == rstVect0) {
        // This is the reset vector page. We need to live-patch
        // the code so the bootloader runs first.
        //
        // Move RESET vector to 'save' vector
	// Save jmp targets (for "Verify")
	rstVect0_sav = buff[rstVect0];
	rstVect1_sav = buff[rstVect1];
	saveVect0_sav = buff[saveVect0];
	saveVect1_sav = buff[saveVect1];

	// Instruction is a relative jump (rjmp), so recalculate.
	uint16_t vect=(rstVect0_sav & 0xff) | ((rstVect1_sav & 0x0f)<<8); //calculate 12b displacement
	vect = (vect-save_vect_num) & 0x0fff; //substract 'save' interrupt position and wrap around 4096
        // Move RESET jmp target to 'save' vector
        buff[saveVect0] = vect & 0xff;
        buff[saveVect1] = (vect >> 8) | 0xc0; //
        // Add rjump to bootloader at RESET vector
        vect = ((uint16_t)main) &0x0fff; //WARNIG: this works as long as 'main' is in first section
        buff[0] = vect & 0xFF; // rjmp 0x1c00 instruction
	buff[1] = (vect >> 8) | 0xC0;
      }
#endif // FLASHEND
#endif // VBP

      writebuffer(desttype, buff, address, savelength);


    }
    /* Read memory block mode, length is big endian.  */
    else if(ch == STK_READ_PAGE) {
      uint8_t desttype;
      GETLENGTH(length);

      desttype = getch();

      verifySpace();

      read_mem(desttype, address, length);
    }

    /* Get device signature bytes  */
    else if(ch == STK_READ_SIGN) {
      // READ SIGN - return what Avrdude wants to hear
      verifySpace();
      putch(SIGNATURE_0);
      putch(SIGNATURE_1);
      putch(SIGNATURE_2);
    }
    else if (ch == STK_LEAVE_PROGMODE) { /* 'Q' */
      // Adaboot no-wait mod
      watchdogConfig(WATCHDOG_16MS);
      verifySpace();
    }
    else {
      // This covers the response to commands like STK_ENTER_PROGMODE
      verifySpace();
    }
    putch(STK_OK);
  }
}

void verifySpace() {
  if (getch() != CRC_EOP) {
    // watchdogConfig(WATCHDOG_16MS);    // shorten WD timeout
    // while (1)			      // and busy-loop so that WD causes
    //   ;				      //  a reset and app start.
  }
  putch(STK_INSYNC);
}

#if LED_START_FLASHES > 0
void flash_led(uint8_t count) {
  do {
    TCNT1 = -(F_CPU/(1024*16));
    TIFR1 = _BV(TOV1);
    while(!(TIFR1 & _BV(TOV1)));
#if defined(__AVR_ATmega8__) || defined (__AVR_ATmega32__) || defined (__AVR_ATmega16__)
    LED_PORT ^= _BV(LED);
#else
    LED_PIN |= _BV(LED);
#endif
    watchdogReset();
  } while (--count);
}
#endif

/*
 * void writebuffer(memtype, buffer, address, length)
 */
static inline void writebuffer(int8_t memtype, uint8_t *mybuff,
			       uint16_t address, pagelen_t len)
{
    switch (memtype) {
    case 'E': // EEPROM
#if defined(SUPPORT_EEPROM) || defined(BIGBOOT)
        while(len--) {
	    eeprom_write_byte((uint8_t *)(address++), *mybuff++);
        }
#else
	/*
	 * On systems where EEPROM write is not supported, just busy-loop
	 * until the WDT expires, which will eventually cause an error on
	 * host system (which is what it should do.)
	 */
	while (1)
	    ; // Error: wait for WDT
#endif
	break;
    default:  // FLASH
	/*
	 * Default to writing to Flash program memory.  By making this
	 * the default rather than checking for the correct code, we save
	 * space on chips that don't support any other memory types.
	 */
	{
	    // Copy buffer into programming buffer
	    uint8_t *bufPtr = mybuff;
	    uint16_t addrPtr = (uint16_t)(void*)address;

	    /*
	     * Start the page erase and wait for it to finish.  There
	     * used to be code to do this while receiving the data over
	     * the serial link, but the performance improvement was slight,
	     * and we needed the space back.
	     */
	    __boot_page_erase_short((uint16_t)(void*)address);
	    boot_spm_busy_wait();

	    /*
	     * Copy data from the buffer into the flash write buffer.
	     */
	    do {
		uint16_t a;
		a = *bufPtr++;
		a |= (*bufPtr++) << 8;
		__boot_page_fill_short((uint16_t)(void*)addrPtr,a);
		addrPtr += 2;
	    } while (len -= 2);

	    /*
	     * Actually Write the buffer to flash (and wait for it to finish.)
	     */
	    __boot_page_write_short((uint16_t)(void*)address);
	    boot_spm_busy_wait();
#if defined(RWWSRE)
	    // Reenable read access to flash
	    boot_rww_enable();
#endif
	} // default block
	break;
    } // switch
}

static inline void read_mem(uint8_t memtype, uint16_t address, pagelen_t length)
{
    uint8_t ch;

    switch (memtype) {

#if defined(SUPPORT_EEPROM) || defined(BIGBOOT)
    case 'E': // EEPROM
	do {
	    putch(eeprom_read_byte((uint8_t *)(address++)));
	} while (--length);
	break;
#endif
    default:
	do {
#ifdef VIRTUAL_BOOT_PARTITION
        // Undo vector patch in bottom page so verify passes
	    if (address == rstVect0) ch = rstVect0_sav;
	    else if (address == rstVect1) ch = rstVect1_sav;
	    else if (address == saveVect0) ch = saveVect0_sav;
	    else if (address == saveVect1) ch = saveVect1_sav;
	    else ch = pgm_read_byte_near(address);
	    address++;
#elif defined(RAMPZ)
	    // Since RAMPZ should already be set, we need to use EPLM directly.
	    // Also, we can use the autoincrement version of lpm to update "address"
	    //      do putch(pgm_read_byte_near(address++));
	    //      while (--length);
	    // read a Flash and increment the address (may increment RAMPZ)
	    __asm__ ("elpm %0,Z+\n" : "=r" (ch), "=z" (address): "1" (address));
#else
	    // read a Flash byte and increment the address
	    __asm__ ("lpm %0,Z+\n" : "=r" (ch), "=z" (address): "1" (address));
#endif
	    putch(ch);
	} while (--length);
	break;
    } // switch
}