Re: [rtl] DMA (latencies and jitter)

[Paolo Mantegazza <mantegazza@aero.polimi.it>]

> Giovanni Racciu wrote:
> 
> It is a matter of fact that heavy DMA can affect (increasing)
> latencies and jitter. In our actual solution the software is running
> on a dedicated PC104 board, which is not corrupting the latency. But
> as a future develpment we would like to put it on a standard PCboard
> and the entire Linux OS plus the applications will run on it (using
> all the hardware features in a massive way).
> Is there anybody who has an idea on how big (worst case) could be the
> increasing latency and gitter ?
> 
> Thank you.

Both NMT-RTL and DIAPM-RTAI have a latency calibration module. I always
got figures that have been confermed by using a scope with a module
generating a square wave, by toglling bits on the parallel port.

Use them with a quiet PC and with it loaded by a lot of disk activity
and network activity and you get what you need, first hand. No chance of
being very precise except by measuring on the very same hardware. So I
suggest you'll do it yourself.

Ciao, Paolo.