Date: Thu, 7 Aug 1997 16:55:06 +0200 (MET DST) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: multimedia@freebsd.org Cc: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Subject: [snddrv] proposal for ioctl change Message-ID: <199708071455.QAA13987@labinfo.iet.unipi.it>
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[foreword: I do not want to criticise the Voxware interface; there
is a reson why it is like it is. It's just that having rewritten the
sound driver from scratch gives me a good chance to cleanup the
interface...]
I am revising the ioctl() interface in the sound driver. In the
voxware scheme, there are over 100 (yes one hundred) different
ioctls, plus about 30 aliases. The pcm interface alone has some 60
calls and 20+ aliases.
In most cases, there are several methods to specify the same actions
(most noticeably stereo). Moreover, often one has to issue several
calls (one to set speed; one to choose between signed, unsigned,
8/16 bit, u/alaw/uncompressed...; another one to set stereo/mono)
to set the data format, and this is quite confusing both for the
programmer and the driver itself, since some combinations might only
make sense if specified all at once (e.g. some boards could do mono
faster than stereo, etc).
No wonder the current structure is quite messy, and I doubt the
programmer really knows how to use it in a sensible way.
SO:
I plan to work on a revised ioctl() interface, using only a handful of
calls for the pcm part, basically three pairs (get & set):
- one for the data format (all parameters in one call, including the
desired buffer size, measured in bytes or time) for each
supported channel (i.e. input, output, and if a board has more
independent channels, they will support all of them);
- one to access the mixers (again, in one call one specifies
mixer, channel, volume, muting, active sources for play & rec...);
- one (or little more) for timing-related issue, i.e. check how many
pending bytes are in the playout/record buffers, flush buffers,
record callbacks in case of mmapped buffers...
I am inspiring to the nice work done on the meteor driver where,
at the beginning, there was a nice effort toward the reduction of
ioctls to set the board parameters.
Are there objections or suggestions on the above ?
In the process I will try to keep compatible with Voxware ioctls(),
(since I have already implemented many of them, it won't cost me much).
Cheers
Luigi
-----------------------------+--------------------------------------
Luigi Rizzo | Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it | Universita' di Pisa
tel: +39-50-568533 | via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522 | http://www.iet.unipi.it/~luigi/
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