Re: [avr-gcc-list] rjmp confusion

[Simon Han]

Thank you for all of these quick replies.
This is what makes this list a *great* list.  :-)

By the way, when I use "-mshort-calls" in avr-gcc in atmega128, will 
avr-gcc warn me if rjmp is not possible?  Note that even if image size 
is greater than 4K words (8K bytes), it might still be possible to use 
rjmp.  Will avr-gcc try to rearrange image such that rjmp is possible 
even if image size is greater than 4K words.

Thanks,
Simon

On Wednesday, February 11, 2004, at 12:03 PM, Rune Christensen wrote:

> Hello
>
> The rjmp use "modulus"/wrapping when calculating the new address in the
> microcontroller.
> So rjmp +1.0k at 3.5k will end up at (3.5k + 1.0k) mod 4k = 0.5k
>
> Best regards
> Rune Christensen
>
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden Behalf Of Simon Han
> Sent: Wednesday, February 11, 2004 8:20 PM
> To: address@hidden
> Subject: [avr-gcc-list] rjmp confusion
>
>
> Hello,
>         Based on AVR instruction set documentation, rjmp is defined to be
> "relative jump to an address within PC - 2K + 1 and PC + 2K (words)".
> Then it says that "for AVR microcontrollers with Program memory not
> exceeding 4K words this instruction can address the entire memory from
> EVERY address location".  I capitalize the word I am confused about.
> How can a rjmp instruction located at flash memory 3.5K jump back to
> flash memory location at 0.5K?  This will require rjmp (-3K).
>         Does avr-gcc generate code at some middle point (say flash memory
> location at 2K) to solve this problem?
>
> Thank you for any help,
> Simon
>
>
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