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Re: [avr-gcc-list] Compiler error creating ISR prologue?
From: |
darkschine |
Subject: |
Re: [avr-gcc-list] Compiler error creating ISR prologue? |
Date: |
Mon, 16 Aug 2010 19:54:08 -0700 (PDT) |
I stand corrected.
It's not often that you need to check for Z result after a clr.
I always thought it was a way of clearing a register while preserving SREG
(since the programmer will know what the result will be anyway)
I guess you would use [ldi 0x00] for that
mrtangent wrote:
>
> Yes, CLR affects SREG (S, V, N, Z).
>
> See <http://www.atmel.com/dyn/resources/prod_documents/doc0856.pdf>
> page 11 (Instruction Set Summary)
> page 54 (CLR – Clear Register)
>
> CLR is just a convenient shorthand for EOR, where the two operands happen
> to be the same register.
>
> Cheers,
>
> --Dave
>
> On Aug 14, 2010, at 1:39 AM, darkschine wrote:
>
>>
>> Are you sure that "clr" has an impact on SREG? I think you should double
>> check...
>>
>>
>> Johannes Bauer wrote:
>>>
>>> On 12.08.2010 18:13, Johannes Bauer wrote:
>>>
>>>> This appears to be strange to me. The "clr r1" instruction should IMO
>>>> be
>>>> placed after the first "push r0" instruction.
>>>
>>> You are wrong, Johannes. It appears to you that the "clr r1" instruction
>>> should be placed after the SREG has been pushed (obviously, as clr also
>>> clears the SREG flags).
>>>
>>> But otherwise, I still think there's a bug :-)
>>>
>>> Regards,
>>> Johannes
>>>
>>> _______________________________________________
>>> AVR-GCC-list mailing list
>>> address@hidden
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>>>
>>>
>>
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