bsp_delay.... Question

[Eric Norum]

Sure, but having a nanosecond resolution on the delay doesn't mean that you should actually expect to get this in all cases.  

I suspect that the man page for this routine would have to discourage its use and to specify that the actual delay could be -10 to +5000% of the requested value since some (many?) implementations might just use a busy loop and would be at the mercy of difference clock speeds, intervening interrupts, etc.

I think that rtems_bsp_delay_nanoseconds is the right resolution.  I'm not sure about the 'delay' part of the name, though.  Perhaps 'spin' or 'loop' might be a better indication of what the routine actually does.

On Apr 25, 2011, at 1:17 PM, Andrei Chichak wrote:

> Alright, I'm going to have to advocate for the little guy.
> 
> At 16Mhz, I would have, at best, 16 instructions at a microsecond.
> 
> A millisecond based delay would be doable using a timer. I could see crafting a loop for a microsecond delay, but nanosecond would be a summer fantasy. 
> 
> Andrei
> 
> 
> On 2011-April-25, at 12:49 PM, Joel Sherrill wrote:
> 
>> On 04/25/2011 11:49 AM, Thomas Doerfler wrote:
>>> Joel,
>>> 
>>> without looking into the existing implementations: I would prefer to
>>> have nanoseconds as a base unit. If we think about systems in the 1GHz
>>> range, having a resolution of 1000 CPU clocks seems a bit outworn to me.
>>> 
>>> 
>> I agree with you Thomas but the existing implementations appear
>> to be in microseconds.  The common name is rtems_bsp_delay().
>> 
>> I wouldn't be opposed to adding an rtems_bsp_delay_nanoseconds()
>> to the set.
>> 
>> Jennifer and I were just looking at this.  The non-uniform nature
>> of this across the BSPs is confusing.
>> 
>> --joel
>>> wkr,
>>> 
>>> Thomas.
>>> 
>>> Am 25.04.2011 18:02, Joel Sherrill wrote:
>>>> Hi,
>>>> 
>>>> Some BSPs have a bsp_delay method.  This is
>>>> a short duration spinner.  We think it is in
>>>> microsecond units but have no idea for sure
>>>> and it could vary by BSP.
>>>> 
>>>> Jennifer and I would like to formalize the
>>>> definition of this.  And standardize it across
>>>> BSPs.  So if it is available, it is safer to
>>>> use. Questions are
>>>> 
>>>> + OK to make a standard BSP method?
>>>> + Microseconds unit?
>>>> 
>>>> If it is not available, what should the stub do?
>>>> 
>>>> Should we have bsp_delay_usecs() and bsp_delay_nsecs?
>>>> 
>>>> Comments appreciated!  Please
>>>> 
>>> 
>> 
>> 
>> -- 
>> Joel Sherrill, Ph.D.             Director of Research&  Development
>> joel.sherrill at OARcorp.com        On-Line Applications Research
>> Ask me about RTEMS: a free RTOS  Huntsville AL 35805
>> Support Available             (256) 722-9985
>> 
>> 
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> 
> 
> 
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-- 
Eric Norum
wenorum at lbl.gov