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

[Theodore A. Roth]

On Sun, 18 Jan 2004, Matte wrote:

> Hi
>
> I'm struggeling with the avr-gcc inline assembler. I want to use the
> inline assembler to optimize code, where I see that the gcc compiler
> does not gives as good code as I want.
>
> I'm currently using the avr-gcc version 3.3.1, with the ATmega16
> microcontroller.
>
> I try to use the following statements (that I found as an example):
>
> uint8_t read(const uint8_t  adr) {
>   uint8_t p;
>   asm volatile ("in %0, %1" : "=r"(p) : "I"(adr));
>   return p;
> }
>
> This gives me the follwing error while compiling:
>
> displaytest.c: In function `read':
> displaytest.c:45: warning: asm operand 1 probably doesn't match
> constraints
> displaytest.c:45: error: impossible constraint in `asm'

Have a look at this:

  http://jubal.westnet.com/AVR/doc/avr-libc-user-manual/FAQ.html#faq_port_pass

>
> I also tried to do the following:
>
> void fastSBI(const uint8_t port, const uint8_t bit) {
>   asm volatile ("sbi %0, %1" : : "I"(port), "I"(bit));
> }
>
> This gives the errors:
> displaytest.c: In function `fastSBI':
> displaytest.c:50: warning: asm operand 0 probably doesn't match
> constraints
> displaytest.c:50: warning: asm operand 1 probably doesn't match
> constraints
> displaytest.c:50: error: impossible constraint in `asm'
>
> Since there clearly is something that I don't understand regarding the
> inline assembler I would like some help on this matter. If there is so
> that the above is correct, there might be some error in the
> configuration of the compilor or the develpoment environmant, then I
> could use some help to solve that problem as well.

You might also want to look this over if you haven't already:

  http://jubal.westnet.com/AVR/doc/avr-libc-user-manual/inline_asm.html

Ted Roth