Re: [Xenomai-core] RTDM and Timer functions

[Philippe Gerum <rpm@xenomai.org>]

Rodrigo Rosenfeld Rosas wrote:
> I really tried to not answer this message and finish the "endless thread" you 
> mentioned, but I couldn't resist. ;) Maybe this will be the last post from my 
> own on this thread and will begin writing in the new thread. See below, 
> please.

Don't bother with self-censorship, AFAIC, the issues you are triggering are 
important ones, since RTDM is a critical piece of the Xenomai framework, and 
allowing users to leverage it efficiently will help us all. However, please don't 
top post and trim the old messages a bit more from your replies: unfortunately, my 
brain has a limited FIFO. TIA,

> ____________________________________________________________
> Em Terça 14 Março 2006 17:29, Jan Kiszka escreveu:
> 
> 
>>...
>>
>>Ok, your framework is effectively aiming for relative times here, that's
>>clear now. But your driver will deliver individual frames with absolute
>>timestamp, right?
> 
> 
> Right.
> 
> 
>>Then it's up to the user to NOT mix up these 
>>timestamps with dates obtained from the system clock. You will have to
>>state this clearly!
> 
> 
> Sure, of course. No problem with that.
> 
> 
>>Moreover, when considering the TSC as high-resolution timestamp source,
>>this is not applicable on SMP / multicore systems. Those tend to have
>>unsynchronised and drifting TSCs. So if the first picture was taken on
>>one CPU and the second on some other...
> 
> 
> Unfortunately I can not arguee on that for now since I know almost nothing 
> about SMP systems. I'll take a look on the topic and hopely soon I'll return 
> you what I think about it.
> 
> 
>>>I'm not talking especifically about this application, but giving you a
>>>general idea of what is not possible to do currently with RTDM if the
>>>application set the timer to periodic.
>>
>>And as I have this general view in mind, I want to avoid that the TSC
>>issue gets exported via RTDM drivers to the user. That's already
>>problematic for the other skins, but having to write special notes all
>>over the documentation of dozens of driver using mixed clocks would be
>>very unhandy.
> 
> 
> I don't understand why adding a new function like this would change a lot the 
> documentation. I really can not see your worries... If you could give me a 
> practical example, maybe it would be easier for me...
> 
> 
>>I see the need for having a high-resolution timestamp aside a
>>low-overhead and low-resolution timer now, 
> 
> 
> good, got an ally. ;)
> 
> 
>>and I think we need to look 
>>for a way to avoid its negative sides.
> 
> 
> First I need to understand better what exactly are the negative sides...
> 
> 
>>Not sure yet if it will be 
>>feasible, but I will come up with a new thread on this topic soon...
> 
> 
> Yes, I've seen. I'll discuss next messages there.
> 
> Thank you,
> 
> Rodrigo.
> 
> 	
> 
> 	
> 		
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-- 

Philippe.