RTEMS4.7 PPC clock API (was Re: IRQ latency )

[Peter Dufault]

On Aug 15, 2005, at 9:17 AM, Kate Feng wrote:

> Peter Dufault wrote:
>
>
>>
>> I use the 64-bit Power-PC time counter, not the system clock, so  
>> the  timings should be very accurate.
>>
>
> It sounds like a good idea to use  PowerPC TBL and TBU as
> a default system clock instead of using the decrementer
> since it reloads itself.
>
>>
>>
>> In an earlier posting I said that if something resets that time   
>> counter I'm in trouble, but I'm 99.99% sure that the time counter  
>> is  left alone.
>>
>> Till will tell.
>>
>>
> Can the decrementer interrupt be disabled for RTEMS4.7 for
> thoses  PPCs  with 64 bit timer since the time counter
> is ideal to be used  as a system clock ?

Can it interrupt?  I thought it just rolled over.  I don't think it  
has a reload register, and the 64 bit counter is too slow for most  
uses.  I know we have some NASA people, maybe they can use it as the  
clock tick on one of the deep space probes.

Also, having a free-running 64 bit low overhead (to read back)  
counter is great for timing analysis and data time stamping, and I'd  
be upset if RTEMS started to reload it for its own reasons.  I  
haven't looked too closely at what's on the MVME5500 but there must  
be a more appropriate clock (one that can both interrupt and has a  
hardware reload value).  I'll check later today.

Peter

>
> Regards,
> Kate
>
>
>
>