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Re: [avr-gcc-list] Re: [avr-libc-dev] [bug #29774] prologue/epilogue sta

From: Ruud Vlaming
Subject: Re: [avr-gcc-list] Re: [avr-libc-dev] [bug #29774] prologue/epilogue stack pointer manipulation not interrupt safe in XMega
Date: Sat, 12 Feb 2011 16:44:06 +0000
User-agent: KMail/1.9.10

On Tuesday 08 June 2010, Matthew wrote:

> So here's what I have found so far. When executing SEI, one more 
> instruction can execute before the first interrupt is serviced. When 
> enabling interrupts by restoring the status register, interrupts can 
> occur immediately. When writing to SPL, interrupts are automatically 
> disabled until the next memory write (up to 4 cycles).
Interesting info!

Can you provide the sources for that or did you test it yourself?
And do these statements hold for xmega en mega alike?

> Therefore, the prologue and epilogue do not need to disable interrupts 
> at all. A write to SPL followed by a write to SPH should be interrupt 
> safe. I have not tested this yet.
This seems hard to test, but is also very interesting.


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