Re: [avr-gcc-list] gcc prolog incorrect?

[Ben L. Titzer]

On Mar 7, 2005, at 8:45 AM, address@hidden wrote:

> So what happens if we get interrupt between 69 and 70? And that 
> interrupt disables interrupts?

In that case, the interrupt handler is broken, since when it returns it 
should restore the interrupt mask to the value it had before the 
interrupt was taken.

> HutchinsonAndy wrote:
>
> > As you describe is exactly what I am concerned about!
> >
> >
> > "Ben L. Titzer" <address@hidden> wrote:
> >
> > > It seems as though the code restores the interrupt mask to exactly as
> > > it was before the call; if the cli were to come first, the I flag 
> > > would
> > > be written to 0 and thus would not be restored correctly.
> > >
> > > The thing I wonder about is what happens if there is an interrupt
> > > between 72 and 73....It seems to me that those two instructions 
> > > should
> > > be swapped...
> > >
> > > On Mar 6, 2005, at 6:12 PM, address@hidden wrote:
> > >
> > > > Is it possible that gcc prolog is incorrect?
> > > >
> > > >   69 000a 0FB6              in __tmp_reg__,__SREG__
> > > >   70 000c F894              cli
> > > >   71 000e DEBF              out __SP_H__,r29
> > > >   72 0010 0FBE              out __SREG__,__tmp_reg__
> > > >   73 0012 CDBF              out __SP_L__,r28
> > > >
> > > > This is the code used to adjust the stack pointer for a regular
> > > > function with interrupts active. Basically it turns of interupts so 
> > > > it
> > > > can chnage both bytes of SP without a problem.
> > > >
> > > > But saved BEFORE interrupts are disabled. Doesn't that mean that if
> > > > interrupts were disabled during ISR, a function could re-enabled 
> > > > them
> > > > when SREG is restored?
> > > >
> > > >
> > > >
> > > > --
> > > > Andy Hutchinson
> > > >
> > > >
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> > --
> > Andy Hutchinson
> >
> >
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> --
> Andy Hutchinson
>
>
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