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Re: [avr-gcc-list] ijmp usage

From: Christian Ludlam
Subject: Re: [avr-gcc-list] ijmp usage
Date: Fri, 20 Dec 2002 13:23:47 +0000
User-agent: POPstar/2.02

On 20 Dec Steve Joiner wrote:

> Ok, dumb question time.  I'm writing a routine in assembly for the atmega8.

> I've got some code that looks like this:

> ldi ZL,lo8(foo)
> ldi ZH,hi8(foo)
> ijmp

> Unfortunately, it doesn't seem to be doing what I want (which would be
> to jump to foo).  If I replace that code, with this code:

> ldi ZL,lo8(foo)
> ldi ZH,hi8(foo)
> rjmp foo

> It works fine.  (I know the two ldi's don't do anything, but I left
> them there to verify that I wasn't trashing some values in Z that I
> needed later).

> I must be interpreting something wrong -- I would think both versions
> should do the same thing.  Can someone give me a clue as to what I'm
> doing wrong?

A guess: ijmp and the PC work with word addresses, whereas the label has a
byte address, so you need to divide it by 2.

ldi ZL,lo8(foo) >> 1
ldi ZH,hi8(foo) >> 1


Christian Ludlam
avr-gcc-list at http://avr1.org

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