CPM command processing

[Leon Pollak]

On Monday, 14 בJanuary 2008, Till Straumann wrote:
> My usual 2-cents:
>
> Busy-waiting with interrupts disabled is evil.
> Such a loop *must* IMHO implement a timeout
> so that the worst-case impact on latency other
> tasks have to suffer from is guaranteed.
Well, if everything works, there should be not more then 20 cycles, thus any 
timeout technique will take more time.
If there is the problem I mentioned, then I do not know what to do, actually.
And we do HW reset, which always helps...
May be there is some method to overcome/recover from the situation...

> -- Till
>
> Leon Pollak wrote:
> > Hello, all.
> >
> > Both files
> > ..lib/libcpu/powerpc/mpc8260/cp.c
> > ..lib/libcpu/powerpc/mpc860/cp.c
> > contain the same code:
> >
> > void m8xx_cp_execute_cmd( uint32_t   command )
> > {
> >   uint16_t   lvl;
> >
> >   rtems_interrupt_disable(lvl);
> >   while (m8260.cpcr & M8260_CR_FLG) {
> >     continue;
> >   }
> >
> >   m8260.cpcr = command | M8260_CR_FLG;
> >   rtems_interrupt_enable (lvl);
> > }
> >
> > The problem with this code is (based on my experience with both CPU's)
> > that it does not check the result of a command execution. Although
> > Motorola's specification states that CPM should finish the command
> > processing in about 20 cycles, my 13 years experience shows that there
> > are cases when the command is not executed and the flag bit remains "1".
> >
> > Therefore, I swap the operators in my code:
> >
> >   m8260.cpcr = command | M8260_CR_FLG;
> >
> >   while (m8260.cpcr & M8260_CR_FLG) {
> >     continue;
> >   }
> >
> > and cause system reset if it remains "1" for too long.
> >
> > I have no explanation to this, because after reset the system returns to
> > the same exactly sequence and now it passes. We have such problem once on
> > each 20-25 units based on MPC8260, but I remember this to occur on MPC860
> > units too.
> >
> > Hope this will be useful...



-- 
            Dr.Leon M.Pollak
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