On Wednesday 10 April 2002 17:39, SIMON Benjamin wrote:
> I'm a beginner with RTLinux...
>
> I have several questions that go in the same way:
>
> Victor Yodaiken has written:
> "The standard RTLinux open will open /dev/x for a fixed set of
> devicesand will not support any other path names" . Which devices are
> supported? for example, can I open /dev/dsp with the RTLinux open
> function?
Any devices that are registered by RTLinux drivers, AFAIK...
> In the case of an RT audio application that reads data on /dev/dsp,
> computes them an plays them back on /dev/dsp, is it necessary to have
> realtime driver for the soundcard?
Yes, and no. For "normal" use of the sound card, you'll need a full
RTLinux driver (or there can be no deterinistic timing!), but there's a
way around this:
* Set the card up in shared memory mode, using the standard
Linux driver.
* Have your RTLinux thread keep track of the playback position
without talking to the standard Linux driver. That is, ask
the card directly, or (probably better) hook the sound card
fragment interrupt with a PLL-like construct.
* Whenever you feel like it (ie when you'r RTLinux thread is
scheduled), write at most (output_position - last_position)
samples into the shared memory buffer.
Of course, you could implement an RTLinux driver that does this
automatically, if you prefer to use the traditional read()/write() API in
your application. You could probably even implement blocking, to make it
work just like in user space.
//David Olofson --- Programmer, Reologica Instruments AB
.- M A I A -------------------------------------------------.
| Multimedia Application Integration Architecture |
| A Free/Open Source Plugin API for Professional Multimedia |
`----------------------------> http://www.linuxdj.com/maia -'
.- David Olofson -------------------------------------------.
| Audio Hacker - Open Source Advocate - Singer - Songwriter |
`-------------------------------------> http://olofson.net -'
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