Re: [avr-gcc-list] in-line assembler

[Wouter van Gulik]

Oke I had some more coffee:

uint8_t get_ram_byte(uint16_t ram_address)
{
    uint8_t    byte;

    asm  ("ld  %[reg], %a[adr]"  "\n\t"
          "st %a[adr], %[reg]"  "\n\t"
    : [reg] "=&r" (byte)
    : [adr] "e"   (ram_address));
    return byte;
}

I only compiled, not assembled...
This compiles and assembles. Note the extra 'a' in front of adr and the 
st instead of sts

HTH,

Wouter


Wouter van Gulik schreef:
> Hi,
>
> I don't know what you intended to do but I guess this is more like it 
> (read the value and write it back):
> I personally prefer the %[] construction.
>
> uint8_t get_ram_byte(uint16_t ram_address)
> {
>     uint8_t    byte;
>
>     asm  ("ld  %[reg] , %[adr]"  "\n\t"
>           "sts %[adr] , %[reg]"  "\n\t"
>     : [reg] "=&r" (byte)
>     : [adr] "e"   (ram_address));
>     return byte;
> }
>
> You're construction of "sts %0, __tmp_reg__" is not correct. GCC is 
> trying to feed sts r24 as first argument, which is invalid.
> You are feeding him the uninitialized variable 'byte'. Which is also 
> allocate to R24.
>
> HTH,
>
> Wouter
>
>
> Robert von Knobloch schreef:
> > Hello,
> > I've been trying to decipher the intricacies of in-line assembler (using
> > the Inline Assembler Cookbook as my guide).
> >
> > I have a very simple application that I cannot seem to realise.
> >
> > I want a C function that will return the contents of the RAM address
> > that I give it as argument.
> >
> > My assembler-based function looks like this:
> >
> > file is hex.c
> > =====
> > uint8_t get_ram_byte(uint16_t ram_address)
> > {
> >     uint8_t    byte;
> >
> >     asm  ("ld __tmp_reg__, %a1"    "\n\t"
> >     "sts %0, __tmp_reg__"    "\n\t"
> >     : "=&r" (byte) : "e" (ram_address));
> >     return byte;
> > }
> >
> > and is called from
> >
> >             rambyte = get_ram_byte(i );
> >             u_hex8out(rambyte);         // Print byte as 8-bit hex.
> >
> > Trying to compile this results in "~/Monitor/hex.c:5: undefined
> > reference to `r24' "
> > If I comment out the line "sts %0, __tmp_reg__"    "\n\t" then it
> > compiles and I see that the parameter is passed in R24,25, copied to
> > R30,31[Z] and the value is read into R0 [__tmp_reg__].
> > I cannot see what is wrong with the sts command or why R24 is mentioned.
> >
> > Can anybody help me ?
> >
> > Many thanks,
> >
> > Robert von Knobloch.
> >
> >
> >
> > _______________________________________________
> > AVR-GCC-list mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
>
>
>
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