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[avr-gcc-list] in-line assembler

From: Robert von Knobloch
Subject: [avr-gcc-list] in-line assembler
Date: Tue, 11 Aug 2009 12:23:18 +0200
User-agent: Thunderbird (X11/20060911)

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.

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