[ECOS] MPC860, hal_delay_us fails

Eric Doenges Eric.Doenges@DynaPel.com
Thu Nov 27 07:35:00 GMT 2003


nprasad3@gmu.edu wrote:
> Hi,
> 
> I am trying to get eCos running on a custom board that has an MPC860 processor. Can someone please provide more insight into this routine and why it fails.
> 
> 1. hal_delay_us - processor stays put in the following loop (*forever*). 
> 
>   do {
>             asm volatile("mfdec  %0;" : "=r"(new_dec) : );        
>         } while (old_dec == new_dec);
> 
> The register values for old_dec and new_dec do not change at all and hence
 > cpu is spinning in it forever. I replaced the routine with a simple 
for loop
 > to simulate delay ofcourse not at all accurately and redboot comes up 
fine.
 > This routine is called in the early phases of redboot (before even
 > redboot writes information so it was giving the false impression that 
there
 > was something seriously wrong with the config).

The way I read PPC documentation, the decrementor should always be
decrementing from the same clock source as the time base counter. Does
your time base counter increment on the 860 ? If it does, the other
possibility is that the compiler wrongly assumes that new_dec doesn't
change in the do ... while loop and falsely optimizes it into an endless
loop - however this seem rather unlikely as other people would have
encountered this problem as well. I think you should check how the time
base clock source is generated on the PPC 860 in general and your board
in particular.
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