Hi All,
I have a problem that I can't figure out. I am passing an unsigned int to a crc check routine that I have written (yes I'm aware there is a gnu function). But for some reason, this code generates an error in the passing of the argument. This can be seen in AVR Studio 4.12..
I have attached the code incase anyone else can see what's going on from the assembler. It doesn't seem to make sense to me!
Here is the code that doesn't work:
Code in main.c ...
#include#include #include #include #include "crc.h" unsigned char buffer_debug[12] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 11, 11 }; unsigned int result; int main( void ) { /* Comms is now setup, and we can send the initialising command for the bootloader */ result = crc_ccit_check( buffer_debug ); while(1){} /* return an exit code */ return(0x0001); }
and the code in crc.c
#include#include #include unsigned int crc = 0x0000; const unsigned int crc_ccit_div = 0x1021; unsigned int crc_ccit_update( unsigned int c, unsigned char dt ) { /* setup the bit counter */ unsigned char bit_count = 8; /* xor the crc with the data (shifted to the high byte */ c = c ^ ((unsigned int)( dt << 8 )); /* loop for 8 bits */ while( bit_count != 0 ) { if( c & 0x8000 ) c = ( c << 1 ) ^ crc_ccit_div; else c <<= 1; /* move to the next bit */ bit_count--; } /* return the crc value */ return(c); } /* Cyclic Redundancy Check */ unsigned char crc_ccit_check( unsigned char *buf ) { /* start a btye counter */ unsigned int i; unsigned int tmp_crc; unsigned char tmp_char; for( i=0; i<10; i++) { tmp_char = *buf; /* Start from the end and work backwards!!*/ tmp_crc = crc_ccit_update( crc, tmp_char ); crc = tmp_crc; buf++; } if( crc == *(buf+(SPM_PAGESIZE/2) ) ) return( 0x01 ); else return( 0x00 ); }
Now, when I simulate this, as soon as the code enters crc_ccit_update, the argument c is passed as 1, not 0 as it should be. In assembler, the code seems to fetch R22 into R18, crc appears to be R18:19 so it messes up the argument...
hmm, after writing this I have a thought that it may be because I am manipulating c and returning it, rather than defining another local. I will check that now.
I'm sure it's something I'm doing and I can't see the wood for the tree's, but I can't figure it out! Has anyone else got some clues?
This is compiled for an ATMEGA128.
BTW, In the bulletin board, when you attach a file and then preview the post, the attachment information is not kept.
