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Re: [avr-gcc-list] __checksum

From: Bob Paddock
Subject: Re: [avr-gcc-list] __checksum
Date: Thu, 29 May 2008 14:13:03 -0400

> I have been successfully porting the old code from IAR to AVR GCC except for
> the followings:

> extern flash unsigned short __checksum;

If your 'checksum' is the last thing after your program,
the equivalent in avr-gcc is __data_log_end[1].

You appear to be trying to do the same as this code:

uint16_t __data_load_end[1]; /* Defined by the linker script.  Set to
address of last byte of .text+.data section */
#include <util/crc16.h>
static __inline__ uint16_t crc_flash_check_has_error( void );
static __inline__ uint16_t crc_flash_check_has_error( void )
  uint8_t  byte_u8;
  uint16_t crc_u16, i;
  uint16_t flash_end_u16 = (uint16_t) &(__data_load_end[0]);

  LED_ASSERT();/* Indicate CRC is in progress after putting in new
batteries or bootloading */
  for( crc_u16 = i = 0; i < flash_end_u16; i++)
       byte_u8 = pgm_read_byte( i );
       crc_u16 = _crc_xmodem_update( crc_u16, byte_u8 );

  if( pgm_read_word( flash_end_u16 ) != crc_u16 )
      return( 1 );/* Bad CRC of memory */
      return( 0 );/* Good CRC */

In your Makefile use this to populate the CRC your 'Checksum' value:

%.hex: %.elf
        @echo $(MSG_FLASH) $@
        $(OBJCOPY) -O $(FORMAT) -R .eeprom $< $@
        mv $@ $(TARGET).org.hex
        srec_cat $(TARGET).org.hex -Intel -Little_Endian_CRC16 -max
$(TARGET).org.hex -Intel -Fill 0xFF -Over $(TARGET).org.hex -Intel
-Cyclic_Redundancy_Check_16_XMODEM -Output $(TARGET).hex -Intel

That way the whole mess is automatic, you don't have to figure out the
CRC each time you change the code.

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