RE: [avr-gcc-list] Problem with stack

[Niklas Lövgren]

Un the other hand this talks about using sei. In the example given the whole
register is restored manually. I guess then it might be in effect
immediately!?

/niklo

-----Original Message-----
From: address@hidden
[mailto:address@hidden On Behalf Of David
Breeze
Sent: den 13 juni 2006 17:42
To: address@hidden; address@hidden
Subject: Re: [avr-gcc-list] Problem with stack

Bjoern,

The following is from the ATmega 128 data sheet.

"When using the SEI instruction to enable interrupts, the instruction
following SEI will be
executed before any pending interrupts, as shown in this example."

Assembly Code Example
sei ; set global interrupt enable
sleep; enter sleep, waiting for interrupt
; note: will enter sleep before any pending
; interrupt(s)
C Code Example
__enable_interrupt(); /* set global interrupt enable */
__sleep(); /* enter sleep, waiting for interrupt */
/* note: will enter sleep before any pending interrupt(s) */

Also when describing RETI

"When the AVR exits from an interrupt, it will always return to the main
program and execute
one more instruction before any pending interrupt is served."

So not totally undocumented.


David



>>> "Haase Bjoern (PT-BEU/EMT)" <address@hidden> 13 June 2006
15:18 >>>
Hi,
 
For AVR there is an undocumented feature that is present to my best
knowledge on all of the AVR devices 
that when enabling IRQs the first IRQ could happen only two instructions
after the "enabling" instruction.
This feature seems to be related to the two-stage pipeline used for the
implementation.

Bjoern.



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