NetBSD/share/man/man9/audio.9

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.Dd October 19, 1997
.Dt AUDIO 9
.Os
.Sh NAME
.Nm audio
.Nd interface between low and high level audio drivers
.Sh DESCRIPTION
The audio device driver is divided into a high level,
hardware independent layer, and a low level hardware
dependent layer.  The interface between these is 
the 
.Va audio_hw_if 
structure.
.Bd -literal
struct audio_hw_if {
	int	(*open)__P((void *, int));
	void	(*close)__P((void *));
	int	(*drain)__P((void *));

	int	(*query_encoding)__P((void *, struct audio_encoding *));
	int	(*set_params)__P((void *, int, int, 
			struct audio_params *, struct audio_params *));
	int	(*round_blocksize)__P((void *, int));

	int	(*commit_settings)__P((void *));

	int	(*init_output)__P((void *, void *, int));
	int	(*init_input)__P((void *, void *, int));
	int	(*start_output)__P((void *, void *, int,
				    void (*)(void *), void *));
	int	(*start_input)__P((void *, void *, int,
				   void (*)(void *), void *));
	int	(*halt_output)__P((void *));
	int	(*halt_input)__P((void *));

	int	(*speaker_ctl)__P((void *, int));
#define SPKR_ON  1
#define SPKR_OFF 0

	int	(*getdev)__P((void *, struct audio_device *));
	int	(*setfd)__P((void *, int));
	
	int	(*set_port)__P((void *, mixer_ctrl_t *));
	int	(*get_port)__P((void *, mixer_ctrl_t *));

	int	(*query_devinfo)__P((void *, mixer_devinfo_t *));
	
	void	*(*allocm)__P((void *, int, size_t, int, int));
	void	(*freem)__P((void *, void *, int));
	size_t	(*round_buffersize)__P((void *, int, size_t));
	int	(*mappage)__P((void *, void *, int, int));

	int 	(*get_props)__P((void *));
};

struct audio_params {
	u_long	sample_rate;		/* sample rate */
	u_int	encoding;		/* ulaw, linear, etc */
	u_int	precision;		/* bits/sample */
	u_int	channels;		/* mono(1), stereo(2) */
	/* Software en/decode functions, set if SW coding required by HW */
	void	(*sw_code)__P((void *, u_char *, int));
	int	factor;			/* coding space change */
};
.Ed
.Pp
The high level audio driver attaches to the low level driver
when the latter calls
.Va audio_attach_mi .
This call should be
.Bd -literal
    void
    audio_attach_mi(ahwp, mhwp, hdl, dev)
	struct audio_hw_if *ahwp;
	struct midi_hw_if *mhwp;
	void *hdl;
	struct device *dev;
.Ed
.Pp
The 
.Va audio_hw_if
struct is as shown above and the
.Va midi_hw_if
is unused (at the moment).  The 
.Va hdl 
argument is a handle to some low level data structure.
It is sent as the first argument to all the functions
in
.Va audio_hw_if
when the high level driver calls them.
.Va dev
is the device struct for the hardware device.
.Pp
The upper layer of the audio driver allocates one buffer for playing
and one for recording.  It handles the buffering of data from the
user processes in these.  The data is presented to the lower level
in smaller chunks, called blocks.  If there, during playback, is
no data available from the user process when the hardware request
another block a block of silence will be used instead.  Furthermore,
if the user process does not read data quickly enough during recording
data will be thrown away.
.Pp
The fields of
.Va audio_hw_if
are described in some more detail below.
Some fields are optional and can be set to 0 if not needed.
.Bl -tag -width indent
.It Dv int open(void *hdl, int flags)
is called when the audio device is opened.  It should initialize
the hardware for I/O.  Every successful call to
.Va open
is matched by a call to
.Va close .
Return 0 on success, otherwise an error code.
.It Dv void close(void *hdl)
is called when the audio device is closed.
.It Dv int drain(void *hdl)
optional, is called before the device is closed or when
.Dv AUDIO_DRAIN
is called.  It should make sure that no samples remain
in to be played that could be lost when 
.Va close
is called.
Return 0 on success, otherwise an error code.
.It Dv int query_encoding(void *hdl, struct audio_encoding *ae)
is used when
.Dv AUDIO_GETENC
is called.  It should fill the 
.Va audio_encoding
structure and return 0 or, if there is no encoding with the
given number, return EINVAL.
.It Dv int set_params(void *hdl, int setmode, int usemode, 
.Dv "struct audio_params *play, struct audio_params *rec)"
.br
Called to set the audio encoding mode.
.Va setmode
is a combination of the
.Dv AUMODE_RECORD
and
.Dv AUMODE_PLAY
flags to indicate which mode(s) are to be set.
.Va usemode
is also a combination of these flags, but indicates the current
mode of the device (i.e. the value of
.Va mode
in the
.Va audio_info
struct).
The
.Va play
and
.Va rec
structures contain the encoding parameters that should be set.
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.
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).
If the device does not have the
.Dv AUDIO_PROP_INDEPENDENT
property the same value is passed in both
.Va play
and
.Va rec
and the encoding parameters from
.Va play
is copied into
.Va rec
after the call to
.Va set_params .
Return 0 on success, otherwise an error code.
.It Dv int round_blocksize(void *hdl, int bs)
optional, is called with the block size,
.Va bs ,
that has been computed by the upper layer.  It should return
a block size, possibly changed according to the needs of the
hardware driver.
.It Dv int commit_settings(void *hdl)
optional, is called after all calls to
.Va set_params ,
and
.Va set_port ,
are done.  A hardware driver that needs to get the hardware in
and out of command mode for each change can save all the changes
during previous calls and do them all here.
Return 0 on success, otherwise an error code.
.It Dv int init_output(void *hdl, void *buffer, int size)
optional, is called before any output starts, but when the total
.Va size
of the output
.Va buffer 
has been determined.  It can be used to initialize looping DMA
for hardware that needs that.
Return 0 on success, otherwise an error code.
.It Dv int init_input(void *hdl, void *buffer, int size)
optional, is called before any input starts, but when the total
.Va size
of the input
.Va buffer 
has been determined.  It can be used to initialize looping DMA
for hardware that needs that.
Return 0 on success, otherwise an error code.
.It Dv int start_output(void *hdl, void *block, int bsize,
.Dv "void (*intr)(void*), void *intrarg)"
.br
is called to start the transfer of
.Va bsize
bytes from
.Va block
to the audio hardware.  The call should return when the data
transfer has been initiated (normally with DMA).  When the
hardware is ready to accept more samples the function
.Va intr
should be called with the argument
.Va intrarg .
Calling
.Va intr
will normally initiate another call to
.Va start_output .
Return 0 on success, otherwise an error code.
.It Dv int start_input(void *hdl, void *block, int bsize,
.Dv "void (*intr)(void*), void *intrarg)"
.br
is called to start the transfer of
.Va bsize
bytes to
.Va block
from the audio hardware.  The call should return when the data
transfer has been initiated (normally with DMA).  When the
hardware is ready to deliver more samples the function
.Va intr
should be called with the argument
.Va intrarg .
Calling
.Va intr
will normally initiate another call to
.Va start_input.
Return 0 on success, otherwise an error code.
.It Dv int halt_output(void *hdl)
is called to abort the output transfer (started by
.Va start_output )
in progress.
Return 0 on success, otherwise an error code.
.It Dv int halt_input(void *hdl)
is called to abort the input transfer (started by
.Va start_input )
in progress.
Return 0 on success, otherwise an error code.
.It Dv int speaker_ctl(void *hdl, int on)
optional, is called when a half duplex device changes between
playing and recording.  It can, e.g., be used to turn on
and off the speaker.
Return 0 on success, otherwise an error code.
.It Dv int getdev(void *hdl, struct audio_device *ret)
Should fill the 
.Va audio_device
struct with relevant information about the driver.
Return 0 on success, otherwise an error code.
.It Dv int setfd(void *hdl, int fd)
optional, is called when
.Dv AUDIO_SETFD
is used, but only if the device has AUDIO_PROP_FULLDUPLEX set.
Return 0 on success, otherwise an error code.
.It Dv int set_port(void *hdl, mixer_ctl_t *mc)
is called in when
.Dv AUDIO_MIXER_WRITE
is used.  It should take data from the
.Va mixer_ctl_t
struct at set the corresponding mixer values.
Return 0 on success, otherwise an error code.
.It Dv int get_port(void *hdl, mixer_ctl_t *mc)
is called in when
.Dv AUDIO_MIXER_READ
is used.  It should fill the
.Va mixer_ctl_t
struct.
Return 0 on success, otherwise an error code.
.It Dv int query_devinfo(void *hdl, mixer_devinfo_t *di)
is called in when
.Dv AUDIO_MIXER_DEVINFO
is used.  It should fill the
.Va mixer_devinfo_t
struct.
Return 0 on success, otherwise an error code.
.It Dv "void *allocm(void *hdl, int direction, size_t size, int type, int flags)"
.br
optional, is called to allocate the device buffers.  If not present
.Xr malloc 9
is used instead (with the same arguments but the first two).
The reason for using a device dependent routine instead of
.Xr malloc 9
is that some buses need special allocation to do DMA.
Returns the address of the buffer, or 0 on failure.
.It Dv void freem(void *hdl, void *addr, int type)
optional, is called to free memory allocated by
.Va alloc .
If not supplied
.Xr free 9
is used.
.It Dv size_t round_buffersize(void *hdl, int direction, size_t bufsize)
optional, is called at startup to determine the audio
buffer size.  The upper layer supplies the suggested
size in
.Va bufsize ,
which the hardware driver can then change if needed.
E.g., DMA on the ISA bus cannot exceed 65536 bytes.
.It Dv "int mappage(void *hdl, void *addr, int offs, int prot)"
.br
optional, is called for
.Xr mmap 2 .
Should return the map value for the page at offset
.Va offs
from address
.Va addr
mapped with protection
.Va prot .
Returns -1 on failure, or a machine dependent opaque value
on success.
.It Dv int get_props(void *hdl)
Should return the device properties; i.e. a combination of
AUDIO_PROP_xxx.
.El
.Pp
The
.Va query_devinfo
method should define certain mixer controls for
.Dv AUDIO_SETINFO
to be able to change the port and gain.
.Pp
If the audio hardware is capable of input from more
than one source it should define
.Dv AudioNsource
in class
.Dv AudioCrecord .
This mixer control should be of type
.Dv AUDIO_MIXER_ENUM
or
.Dv AUDIO_MIXER_SET
and enumerate the possible input sources.
For each of the named sources there should be
a control in the
.Dv AudioCinputs
class of type
.Dv AUDIO_MIXER_VALUE
if recording level of the source can be set.
If the overall recording level can be changed (i.e. regardless
of the input source) then this control should be named
.Dv AudioNrecord
and be of class
.Dv AudioCinputs .
.Pp
If the audio hardware is capable of output to more than
one destination it should define
.Dv AudioNoutput
in class
.Dv AudioCmonitor .
This mixer control should be of type
.Dv AUDIO_MIXER_ENUM
or
.Dv AUDIO_MIXER_SET
and enumerate the possible destinations.
For each of the named destinations there should be
a control in the
.Dv AudioCoutputs
class of type
.Dv AUDIO_MIXER_VALUE
if output level of the destination can be set.
If the overall output level can be changed (i.e. regardless
of the destination) then this control should be named
.Dv AudioNmaster
and be of class
.Dv AudioCoutputs .
.Sh SEE ALSO
.Xr audio 4
.Sh HISTORY
This
.Nm
interface first appeared in
.Nx 1.3 .