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The SBI instruction only modifies one bit (0-7) at a time.  You are trying
to modify a whole byte.

The compiler probably generates a IN, ORI , OUT instruction sequence.  One
of the weird things about AVR is that I/O access is bit oriented (since
often you only want to play with one bit of a register) while the register
bit manipulation is byte wide.  In fact, there are no CBR/SBR instructions,
they are assembler aliases for ANDI and ORI...  I am not sure why Atmel put
those there since they are very confusion when put along side the SBI/CBI
instructions.

You could save one word by doing two SBI's...

Cheers!

-----Original Message-----
From: jay marante

i have this code with ICCAVR:

TCCR1A |= (1<<COM1A1)|(1<<COM1A0);

i wanted to replace that code with this assembly code:

asm("SBI TCCR1A,COM1A1+COM1A0\n");

because i found out that the assembly code that the compiler generate has
three sets of instructions. i think that if i replace the C code with the
corresponding assembly code, i might optimize the flash memory.

but i get this error when i compile it:

"absolute expression expected"

what's wring with my code? did i get it right?
thanks for the help.

At 05:18 AM 6/3/2004 -0700, Larry Barello wrote:
>The SBI instruction only modifies one bit (0-7) at a time.  You are trying
>to modify a whole byte.

Very easily confused with SBR and CBR (Which I for one would just like to 
tear out of the assembler), Set BITS in register, and clear BITS in 
register... Just ORI and ANDI instructions re labeled.

Glad to find this post. It showed me how to embed assembly code in 
the C code. Does anyone know if there is some ICCAVR documentation 
introducing how to embed assembly code in the C code? I cannot find 
in their help documentation at all.

Thanks!

Yang



--- In AVR-Chat@yahoogroups.com, jay marante <jaythesis@y...> wrote:
> i have this code with ICCAVR: 
> 
> TCCR1A |= (1<<COM1A1)|(1<<COM1A0); 
> 
> i wanted to replace that code with this assembly code: 
> 
> asm("SBI TCCR1A,COM1A1+COM1A0\n"); 
> 
> because i found out that the assembly code that the compiler 
generate has three sets of instructions. i think that if i replace 
the C code with the corresponding assembly code, i might optimize the 
flash memory. 

> 
> but i get this error when i compile it: 
> 
> "absolute expression expected" 
> 
> what's wring with my code? did i get it right? 
> thanks for the help.
> 
> 
> 		
> ---------------------------------
> Do you Yahoo!?
> Friends.  Fun. Try the all-new Yahoo! Messenger