Subject: Re: [linux-audio-dev] Realtime
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: Wed Jun 28 2000 - 06:20:15 EEST
>> - multimedia apps need to interact with multimedia devices (soundcard,
>> framebuffer, MIDI interface etc) , thus using RTLinux would require a complete
>> rewrite of all these drivers.
>> no chance.
>
>I don't see why it would require a "complete rewrite".
the ALSA drivers currently represent a minimum of 64000 C statements
(i counted semicolons in the files; there are 174,000 lines in total,
including comments).
although i strongly suspect that most of the work involved in porting
them to RTLinux could be done with a portability "wrapper", i also
strongly suspect that we'd have to go over every single line of every
file and check it for various assumptions.
the doesn't include the video/tv interfaces needed by actual
MULTI-media apps (as opposed to multi-media).
no, its not a "complete rewrite", but its about as close to it as you
can get without it actually becoming one.
>RTLinux modules are like drivers -- if you can accept drivers in kernel
>space, you should not have a problem with RT components.
Au contraire. Drivers are, ideally, "write once" programs. In the real
world, its never quite like that, but once a device driver is done,
its done, and changes are only usually necessary when a kernel API
change occurs or some new information about the device comes to light.
By contrast, actual applications tend to keep changing, and often in
dramatic and comprehensive ways. This makes it hard to feel confident
about running an RT component, whereas its fairly easy to feel quite
safe about a driver that has been in use for a month or so.
> RT part:
> do{
> samples
> computes using table share with user code
> outputs to device and to shared memory
> check commands, if any, from user app
> }
not a bad summary from someone who knows absolutely nothing about the
field. <wink>
i think, however, that all of this is moot. For almost all of us, the
performance offered by Ingo's patches to 2.2.{10,11,12,13,14,15} is
more than adequate. Using RTLinux involves, at the absolute minimum,
some real work, a definite learning experience, and possibly a
redesign of already operational applications. To gain what ? Better
performance than we actually need. victor, its a tough sell ;)
--p
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