Re: [avr-gcc-list] inline assembler problem

[Christoph Plattner]

Hello !

I HAVE GOT IT !

The varible "bit" is an input not an output parameter !!
So it is in the wrong line of the __asm__ __volatile__ statement !
I think you have to write:

        __asm__ __volatile__ (
                "code...." "\n\t"
                .
                .
                "code...." "\n\t"
                : "=r" (crchi), "=r" (crclo)
                : "0" (crchi), "1" (crclo), "=r" (bit)
                : "r24", ....   << registers that may be modified and
                                   the compiler has to concern about !
        );

Further: what is "=&r" ? I only know "=r", and if I want to reference
a memory (pointer), then "=m" is used.

With friendly regards
        Christoph P.


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Michael Jochum wrote:
> 
> hi all!
> 
> i am writing a crc function and cant get the inline asm code to work.
> the pure c-code is working.
> as you can see in crc.s the cpc instruction gets the wrong parameter.
> what is the problem with this code?
> 
> i use:
>   gcc version 3.0.1 20010806 (prerelease)
>   binutils version version 2.11.90 20010814
>   avr-libc-20010717
> 
> and cmd is:
>   avr-gcc -O3 -mmcu=at90s4433 -c crc.c -S -o crc.s
> 
> tia,
> michael.
> 
> --- crc.asm ---
> #include <io.h>
> 
> static unsigned char crchi;
> static unsigned char crclo;
> 
> void crcbit(unsigned char bit){
> #if 1
>       asm volatile(
>               "clc"                             "\n\t"
>               "ror %0"                          "\n\t"
>               "ror %1"                          "\n\t"
>               "cpc %2,__zero_reg__"             "\n\t"
>               "breq crc_skip_op"                "\n\t"
>               "push r24"                        "\n\t"
>               "ldi r24,0x84"                    "\n\t"
>               "eor %0,r24"                      "\n\t"
>               "ldi r24,0x08"                    "\n\t"
>               "eor %1,r24"                      "\n\t"
>               "pop r24"                         "\n\t"
>               "crc_skip_op:"                    "\n\t"
>               : "=r" (crchi), "=r" (crclo), "=&r" (bit)
>               :  "0" (crchi), "1" (crclo)
>               : "0", "1"
>               );
> #else
>  unsigned char tmp = crclo & 1; //rotate the 16 bits to the right
>  crclo = crclo >> 1;
>  crclo |= (crchi & 1) << 7;
>  crchi = crchi >> 1;
> 
>  if (((tmp & 0x01)^bit) ==0x01){
>    crchi = crchi^0x84;
>    crclo = crclo^0x08;
>  }
> #endif
> }
> 
> main() {
>   crclo=crchi=0xff;
>   for(;;) {
>     crcbit(1);
>     crcbit(0);
>   }
> }
> 
> --- crc.s ---
>         .file   "crc.c"
>         .arch at90s4433
> __SREG__ = 0x3f
> __SP_H__ = 0x3e
> __SP_L__ = 0x3d
> __tmp_reg__ = 0
> __zero_reg__ = 1
> _PC_ = 2
>         .text
> .global crcbit
>         .type   crcbit,@function
> crcbit:
> /* prologue: frame size=0 */
> /* prologue end (size=0) */
>         lds r19,crchi
>         lds r18,crclo
>         mov r20,r19
>         mov r22,r18
> /* #APP */
>         clc
>         ror r20
>         ror r22
>         cpc r18,__zero_reg__     <<<< problem
>         breq crc_skip_op
>         push r24
>         ldi r24,0x84
>         eor r20,r24
>         ldi r24,0x08
>         eor r22,r24
>         pop r24
>         crc_skip_op:
> 
> /* #NOAPP */
>         mov r21,r20
>         mov r18,r22
>         sts crchi,r21
>         sts crclo,r18
> /* epilogue: frame size=0 */
>         ret
> /* epilogue end (size=1) */
> /* function crcbit size 39 (38) */
> .Lfe1:
>         .size   crcbit,.Lfe1-crcbit
> .global main
>         .type   main,@function
> main:
> /* prologue: frame size=0 */
>         ldi r28,lo8(__stack - 0)
>         ldi r29,hi8(__stack - 0)
>         out __SP_H__,r29
>         out __SP_L__,r28
> /* prologue end (size=4) */
>         ldi r18,lo8(-1)
>         sts crchi,r18
>         sts crclo,r18
> .L3:
>         ldi r24,lo8(1)
>         rcall crcbit
>         ldi r24,lo8(0)
>         rcall crcbit
>         rjmp .L3
> /* epilogue: frame size=0 */
> __stop_progIi__:
>         rjmp __stop_progIi__
> /* epilogue end (size=1) */
> /* function main size 15 (10) */
> .Lfe2:
>         .size   main,.Lfe2-main
>         .lcomm crchi,1
>         .lcomm crclo,1
> /* File crc.c: code   54 = 0x0036 (  48), prologues   4, epilogues   2
> */
> 
> _______________________________________________
> avr-gcc-list mailing list
> address@hidden
> http://avr.jpk.co.nz/mailman/listinfo/avr-gcc-list

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