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Update struct audio_params and description of set_params(). 

Feel free to correct my poor English ;-)
This commit is contained in:
kent 2002-03-11 15:09:51 +00:00
parent 289a98c007
commit d1b86e1e52
1 changed files with 67 additions and 3 deletions
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70
share/man/man9/audio.9
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@ -1,4 +1,4 @@
.\" $NetBSD: audio.9,v 1.19 2001/10/03 20:50:31 augustss Exp $
.\" $NetBSD: audio.9,v 1.20 2002/03/11 15:09:51 kent Exp $
.\"
.\" Copyright (c) 1999, 2000 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -34,7 +34,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd February 11, 2000
.Dd March 11, 2002
.Dt AUDIO 9
.Os
.Sh NAME
@ -103,6 +103,18 @@ struct audio_params {
/* Software en/decode functions, set if SW coding required by HW */
void (*sw_code)(void *, u_char *, int);
int factor; /* coding space change */
/*
* The following four members represent what format is used in a
* hardware. If hw_sample_rate != sample_rate || hw_channels !=
* channels, the audio framework converts data. Encoding and
* precision are converted in sw_code().
* set_params() should set correct values to them if no conversion is
* neede.
*/
u_long hw_sample_rate;
u_int hw_encoding;
u_int hw_precision;
u_int hw_channels;
};
.Ed
.Pp
@ -190,15 +202,67 @@ The
and
.Va rec
structures contain the encoding parameters that should be set.
.Pp
If the hardware requires software assistance with some encoding
(e.g., it might be lacking mulaw support) it should fill the
.Va sw_code
and
.Va factor
fields of these structures.
fields of these structures with translation information, and
set to hw_* fields what format the hardware actually uses.
For example, if
.Va play
requests [8000Hz, mulaw, 8bit, 1ch] and the hardware supports
not 8bit mulaw but 16bit slinear_le, the driver should set
.Va mulaw_to_slinear16_le
to
.Va sw_code ,
2 to
.Va factor ,
.Dv AUDIO_ENCODING_SLINEAR_LE
to
.Va hw_encoding
and 16 to
.Va hw_precision .
The values of the structures may also be modified if the hardware
cannot be set to exactly the requested mode (e.g. if the requested
sampling rate is not supported, but one close enough is).
.Pp
The hardware driver can also request sampling rate conversion
and mono-stereo conversion. If
.Va set_params
sets to
.Va hw_sampling_rate
a value which is different than
.Va sampling_rate
or sets to
.Va hw_channels
a value which is different than
.Va channels ,
and set
.Dv AUDIO_ENCODING_SLINEAR_LE
to
.Va hw_encoding ,
the hardware independent driver performs sampling rate and/or mono-stereo
conversion. If such conversion is not needed,
.Va set_params
must keep
.Va sampling_rate
and
.Va channels
are the same as
.Va hw_sampling_rate
and
.Va hw_channels
respectively.
.Pp
Note: The order of conversion is
.Va sw_code
followed by sampling rate and mono-stereo in playing,
and sampling rate and mono-stereo followed by
.Va sw_code
in recording.
.Pp
If the device does not have the
.Dv AUDIO_PROP_INDEPENDENT
property the same value is passed in both