IRQ latency (was Re: RTEMS-MVME5500 BSP v1.3 available)

[Till Straumann]

Peter Dufault wrote:

>
> On Aug 10, 2005, at 8:36 PM, Kate Feng wrote:
>
>
>>
>> Peter Dufault  wrote :
>>
>>
>>
>>> Me? No, I *never* disable interrupts! (well, almost never).
>>>
>>>
>>
>> Yes, it's better to limit it to the minimum.
>>
>>
>>
>>> But seriously, no I didn't disable interrupts. I'm a firm believer in
>>> lock-free systems, which to my thinking means trying to push the
>>> locks down to the hardware level.
>>>
>>>
>>
>> I  am not sure  if you will get an  accurate timestamp in you test as
>> you mention  that you use  system clock, especially  under the heavy
>> load.   Anyway,  Till should make a  conclusion about  its pedigree.
>> He is the one who made the enhancement  in RTEMS4.7 PPC
>> shared port.
>>
>>
>>
>
> Kate asked me off-list if I'd disabled interrupts in my timings, and  
> this is how I responded.  I'd have been less tongue-in-cheek on-list,  
> but it's OK with me for anyone forward my emails unless I say not to.
>
> I use the 64-bit Power-PC time counter, not the system clock, so the  
> timings should be very accurate.
>
> 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.

AFAIK, the PPC TB is never (re)-set / changed. I also use it for timing 
purposes.

-- Till

>
> Till will tell.
>
> Peter
>