Re: [avr-gcc-list] COMPILER Frame pointer bug!!!

[Christoph Plattner]

I also thougt about this problem, but if all routines locking interrupts
or modifying the stats register are written in the correct way (with
restoring flags) then, there is NO problem, if there is an interruption
within save-flags and CLI. Because the interrupt has to restore the
flags, so everything has a consistent state. The most CPU architectures
I know, cannot save the flags and CLI in an atomic way.

With friendly regards
Christoph P.



Bernd Felsche wrote:
> 
> Christoph Plattner tapped away at the keyboard with:
> 
> > No the code is OK, you simple have overseen the interrupt handling.
> >
> > Using cli/sei is ALWAYS WRONG and many old operating system errors
> > have to be searched. The correct handling is (used C style to
> > explain):
> >
> > flags = save_cpu_flags ();    /* inlcuding Interrupt Enable bit */
> > cli ();                               /* disable interrupts */
> >
> > < critical code >
> >
> > restore_cpu_flags (flags);    /* set the old IE state !!! */
> 
> Unfortunately, there's the opportunity for an interrupt to occur
> between the save and the interrupt disable. Or did I miss something
> in the instruction set details?
> 
> This is pretty much a short-coming of the AVR. If the cli() and
> sei() were both save the previous status of the interrupt flag to
> (say) the carry bit, then the previous state could be restored
> reliably, under all circumstances.
> 
> [snip]
> 
> --
>  /"\  Bernd Felsche - Innovative Reckoning, Perth, Western Australia
>  \ /      ASCII ribbon campaign | I'm a .signature virus!       |
>   X       against HTML mail     | Copy me into your ~/.signature|
>  / \      and postings          | to help me spread!            |

-- 
-------------------------------------------------------
private:        address@hidden
company:        address@hidden