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

[Wouter van Gulik]

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