[wdmaudiodev] Re: Real Time Processing
- From: Waldemar Haszlakiewicz <waldemar.haszlakiewicz@xxxxxxxx>
- To: Pieterjan Demarcke <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Sat, 5 Mar 2005 11:23:47 +0100
If you want you can add your code even to the interrupt routine.
With that you can get latency down to less than 1ms, but take notice that this
is against
the WinXP driver good behavior, as interrupt routine should be a s fast as it
can get, so that
you don't stall the other parts of the system. Like some device needs a fast
response from the
system just to fix some flag or something. So if you'll do a lot of processing
in the interrupt
routine the system can start "hiccuping".
Ok now if I remember you previous mail you are doing just some really simple
calculations right?
So if the machine isn't an old one there should be no worry.
Now all you need is a direct access to cards buffers, set the cards interrupt
to something like
32samples (or less) and do your simple calculations.
Now the only problem is that communication with the card is much, much slower
than speeds of the
CPUs. So the other way (and from the eyes of Microsoft the right way) around
would be to do all
your stuff in DPC which as you said. The latency of 32samples can be easily
achieved so....
Now you have 2 options:
- interrupt way -> can get really small latencies, but it's not in the way a
good driver should behave
- DPC way -> latency would be a little higher than with interrupt way, but
still much smaller than
if you would send the data to user level and what is most important the driver
will not offend any
"good driver laws"
Peace
Waldemar
PD> Thank you for all the inputs, I will consider them. Also there's one
PD> thing that seemed to be an option, but I don't know if it's possible:
PD> could I write a customDPC that processes each sample and writes it
PD> immediatly back to the line-out AND to a dedicated buffer (so i can
PD> acess the value from an user interface)? I'm not good aware of the
PD> possibilities of a DPC, but it seems to me that it stands the closest
PD> to the hardware. But maybe this isn't correct. Anyway thank you for
PD> all the idea's, you all helped me a lot already.
PD> Pieterjan
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