"Marco Randazzo" <[EMAIL PROTECTED]> wrote: > I would like to pass a simple input value to an asm routine but compiler = > says "error: impossible constraint in `asm'" and I can't understand what = > I've to do. Here is my code:
> uint8_t servo_prot_offset; > [...] > asm volatile ( > "\n" > "PUSH R18" "\n\t" > "PUSH R24" "\n\t" > "PUSH R25" "\n\t" > " LDI R24,0x00" "\n\t" > " LDI R25,0x00" "\n\t" > "l1 : ADIW R24,0x01" "\n\t" > " LDI R18,0x06" "\n\t"=20 > " CPI R24,%0 " "\n\t" <--- HERE I WANT COMPARE R24 WITH = > THE VALUE OF servo_prot_offset > " CPC R25,R18 " "\n\t" > " BRCS l1" "\n\t" > "POP R25" "\n\t" > "POP R24" "\n\t" > "POP R18" "\n\t" > : //output operands > : "M" (servo_prot_offset) //input operands > ); See the inline assembler documentation (part of avr-libc docs). Constraint "M" would expect an 8-bit integer constant, but you're trying to pass an 8-bit variable, yet your CPI instruction would expect a constant literal again. Something doesn't fit right together. Perhaps you try first expressing your desire in C. Did you verify the generated code from C? Also, don't push/pop your own stuff. Instead, use the "clobbers" section of the inline asm statement to tell the compiler which registers you are destroying, or even better, invent a couple of scratch variables in the surrounding C code, and pass them down to your inline asm statement (e.g. using "d" constraints). Also, you are always allowed to use __tmp_reg__ as a scratch register. That way, you'll give the compiler freedom to arrange the register usage appropriately, so most likely, no additional push/pop operations will be required at all. -- cheers, J"org .-.-. --... ...-- -.. . DL8DTL http://www.sax.de/~joerg/ NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-) _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
