Re: [microblaze-uclinux] usleep

[aurash <aurelian.lazarut@xxxxxxxxxxx>]

Guys,
another approach here could be the hardware (don't forget the whole 
thing is configurable platform)  a dedicated peripheral will give 
accurate timing and will leave CPU time for other "high level" things.

my 2 penny
Aurash


John Williams wrote:

> Hi Jay, Yasshi,
>
> Yasushi SHOJI wrote:
>
>> At Mon, 25 Oct 2004 13:53:44 -0600,
>> Jay Norrish wrote:
>
>
>>> I am trying to use the usleep() function to
>>> put my application to sleep while my peripherals
>>> do data acquisition but, I have not been able to get
>>> the function to have a resolution of less than 10ms
>>> which is the tick rate.
>>
>
> A quick surf in the sources explains why - the usleep() lib call 
> translates to a nanosleep() syscall, which is implemented in the 
> kernel with a schedule_timeout().  At first glance, the only way 
> you'll get a wakeup before 10ms is if you are under heavy interrupt 
> load from a ping flood or similar.
>
> It seems this is an established limitation of usleep.  I see some 
> mailing list threads proposing ways to improve it etc, but none of 
> these have been implemented in microblaze.
>
>>> I know I could change the tick rate
>>> with the #define HZ in the mb_vannilla.h file but I am worried that 
>>> it will
>>> break other programs.
>>
>>
>> I wouldn't recommend to change HZ for 2.4, if you don't know the
>> kernel internal.  it might or might not work.
>
>
> Oh but it's definitely worth a try!  ;-)   Please let us know what 
> happens...
>
>>> Is there another function or way to do this ?
>>
>>
>> use bigger fifo and/or interrupt.  even with those, timing is not
>> guaranteed.  Linux is not a realtime os after all.
>
>
> Perhaps you might consider a sort of busy-wait loop with calls to 
> gettimeofday() - it offers near microsecond resolution.  It's not very 
> friendly to other processes in the system, but if your wait is much 
> shorter than the tick interval (which it must be, otherwise usleep() 
> would suffice), then it mightn't matter too much.
>
> Cheers,
>
> John
>
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>


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