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

[David Breeze]

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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