Re: [avr-gcc-list] Assembler error message

[Jens Andersen]

Hi Robert,

I think that your problems come from the fact that the CBR instruction
requires
a register as the target, and as you want to modify a variable, this
wont work.

I assume that what you want to do, is to clear one or more bits in a
variable,
using a bit mask, so maybe you could try this.

//IR_Status variable
#define IR_Avail 128

volatile unsigned char IR_Status = 0x20;

#define CLEARBIT_CONST(var, mask) (var &= ~mask)

void main(void)
{
  CLEARBIT_CONST(IR_Status, IR_Avail);
}

Compiled with option -O2 this generates the following assembler code.

  10:test.c        ****   CLEARBIT_CONST(IR_Status, IR_Avail);
  56                            .stabn 68,0,10,.LM2-main
  57                    .LM2:
  58 0008 8091 0000             lds r24,IR_Status
  59 000c 8F77                  andi r24,lo8(127)
  60 000e 8093 0000             sts IR_Status,r24
  11:test.c        **** }

I think that this is as best as you can get it. :)

Best regards
Jens Andersen

Robert Rozman wrote:
> 
> Hello,
> 
> thanks for response. Only one short question:
> - I'd like macro CLEARBIT_CONST to influence value of variable 'var'. Do I
> have to add something to output section of macro too - as it is now, it
> seems like it doesn't have any output or influence on variable.
> 
> Thanks in advance,
> 
> Robert Rozman
> 
> -----Izvorno sporoèilo-----
> Od: Denis Chertykov <address@hidden>
> Za: Robert Rozman <address@hidden>
> Kp: address@hidden <address@hidden>
> Datum: 16. marec 2001 20:17
> Zadeva: Re: [avr-gcc-list] Assembler error message
> 
> >Try to use:
> >
> >#define CLEARBIT_CONST(var,mask) \
> > asm volatile (\
> >  "andi %0, lo8(0xff - (%1)) "\
> >  : /* no outputs */\
> >   : "r" ((u08) (var)), \
> >    "i" ((u08) (mask)) \
> >       )
> >
> >
> >Or:
> >
> >#define CLEARBIT_CONST(var,mask) \
> > asm volatile (\
> >  "cbr %0, %1) "\
> >  : /* no outputs */\
> >   : "r" ((u08) (var)), \
> >    "i" ((mask)) /* <-------- type casting to u08 removed */ \
> >       )
> 
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