Timer-based scheduling model has some merits against IRQ-based
scheduling model. However, as of Linux kernel v4.21, ALSA PCM interface
between kernel/userspace has a lack of some features.
This commit adds a subsection to describe it.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit fulfills a subsection titled as 'Timer-based scheduling model'.
This scheduling model is introduced in a recent decade. In this model,
applications should take care of its timing to operate sampled data
according to any timer. This is an optional behaviour of runtime of
PCM substream.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds a section titled as 'SCHEDULING MODEL' and fulfill a
subsection titled as 'IRQ-based scheduling model'.
This scheduling model is for a typical applications to operate a kind of
data sampled against actual time. In this model, ALSA PCM core maintains
timing of the applications with notification of hardware by
blocking/waking up their processes. This is a default behaviour of
runtime of PCM substream.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
At present, some options for software parameters have actual effects in
cases neither mmap operation nor timer-based scheduling model is used.
For mmap operation, backward compatibility to aplay(1) is lost.
This commit adds descriptions about it.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit attempts to describe purpose of each option with more texts
than aplay(1).
I note that a section for scheduling model will be prepared near future.
This commit just adds a placeholder for the section.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit attempts to categorise existing options to four parts;
basics, software features, libasound plugin options and debug assistant.
These categories will assist users to get purpose of each option.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
I note that libffado backend has no support for suspend/resume because
libffado has enough implementation for these features even if it exports
some symbols for them. For this backend, reception of signals for the
features brings abortion of runtime.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Some items in a section for POSIX SIGNALS includes wrong texts.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
A line has meaningless 'H' letter in its end.
Fixes: c5b2beebfd ('axfer: add a manual for entry point')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
A function, print_help() in xfer module is defined to return integer
value, however this is useledd.
This commit fixes it.
Fixes: 908ff69be2 ('axfer: print help text of transfer subcommand just for common options')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds an operation for xfer backend to print help text.
In this time, content of the help is not implemented yet.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds help text of transfer subcommand.
In this time, backend options are not described. They will be added in
future commits.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds help text of list subcommand.
This help text can not be in execution of alias (aplay/arecord) due to
program design.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds help text of command entry. This is printed when
help subcommand is given, or a valid subcommand or a valid direction
are not given.
Unfortunately, at present, execution of alias (aplay/arecord) with help
options prints the added help text. It should print help options in
transfer subcommand. This bug will fixed in future commits.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
An implementation of transfer subcommand is the most large part and
complicated somehow. This commit adds a section titled 'DESIGN' to
manual to overall design of the subcommand.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
The axfer(1) is designed to keep backward compatibility to aplay(1)
as much as possible, however some changes are added to its behaviour.
This commit adds a section titles 'COMPATIBILITY TO APLAY' to each
manuals.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds a manual for transfer subcommand in axfer(1). This
subcommand is a main feature of this command, to transfer audio data
frame between device/node and file/stdio.
This subcommand is designed to have several transmission backend.
Detail explanation about these backends is added in future commits.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds a manual for list subcommand of axfer(1). At present,
this subcommand prints helpful information to transfer subcommand in
libasound backend.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds a manual for axfer(1). This command is an entry point
to supported subcommand.
I note that axfer(1) has renewed option system against aplay(1). The
command get positional two options for subcommand and direction. In
short:
$ axfer transfer capture|playback [options for transfer subcommand]
$ axfer list capture|playback [options for list subcommand]
$ axfer version
$ axfer help
Manuals to subcommands are added later separately.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
A reference to a terminal for standard input/output brings some
troubles. For capture transmission, it can bring some terminal
control codes and it's possible to make the terminal in disorder.
For playback transmission, it can bring endless loop to read
data for detection of type of container.
This commit checks whether a terminal is referred for the standard
input/output by a call isatty(3). When detecting a terminal,
axfer run time prints message and goes to finish.
Suggested-by: Takashi Iwai <tiwai@suse.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
When subcommands are operated, top-most two arguments are already
parsed in renewed command system, thus they're useless. Besides,
they're possible to be parsed by getopt_long(3).
This commit truncates these options before entering subcommand
operation.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
At present, both of help and transfer subcommands are used when options
are missing in compatibility mode to aplay(1). However, in a view of
users, it should be transfer subcommand.
This commit uses transfer subcommand as a default for the mode.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In renewed command system, axfer uses first argument for subcommand. In
popular subcommand such as transfer, transmission direction is required.
At present, some options in aplay(1) are used for this purpose however
it's understandable to use second argument for this purpose.
This commit uses second argument as fixed position to indicate
direction for renewed command system.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit splits option parser for new command system into a function
for readability.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit splits option parser for backward compatibility to aplay(1)
in list subcommand. Supported operations are listed in local enumeration.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
At present, axfer is designed to use several types of backend for
transmission of data frames. This commit is an implementation
example of the backend.
Libffado is a userspace library for transmission of data frames according
to protocols similar to IEC 61883-1/6. This library handles audio and
music units on IEEE 1394 bus.
Unfortunately, this library executes ctor/dtor of instances for some
objects in startup/finish routines of C runtime. As a result, it outputs
some superfluous messages even if the backend is not actually used.
Furthermore, this library brings memory leak internally. Therefore,
it's not practical to build this backend for generic purposes. Although
the backend implementation works fine, this commit is just for technical
preview.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Althogh many options are actually supported by aplay, some of them are
not enough good in practical points. For example, '--test-position'
option is meaningless for some use cases. Furthermore, due to practical
reasons, some options are not implemented well; e.g. vumeter.
This commit marks such options as 'obsoleted'.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In 2010, ALSA PCM interface got an flag of hardware parameters to suppress
periodical interrupts, according to a request from PulseAudio developer.
In typical PCM operation for usual hardware, PCM drivers configure the
hardware to generate the periodical interrupts to notify that the same
amount of data frames as a period of PCM buffer is actually transferred
via serial sound interface. The flag can suppress this if the driver
support it.
There's some merits of this configuration:
- No interrupt context run for PCM substream. The PCM substream is
handled in any process context only. No need to care of race
conditions between interrupt/process contexts. This is good for
developers of drivers and applications.
- CPU time is not used for handlers on the interrupt context. The CPU
time can be dedicated for the other tasks. This is good in a point
of Time Sharing System.
- Hardware is not configured to generate interrupts. This is good in a
point of reduction of overall power consumption.
Disabling period interrupt is used for 'Timer-based scheduling' to
consume data frames on PCM buffer independently of interrupt context. As
noted, no interrupt context runs for PCM substream, thus any blocking
operation is not released. Furthermore, system calls for multiplexed I/O
is not also released without timeout.
In this scheduling model, applications need to care of available space on
PCM buffer by lapse of time, typically by yielding CPU and wait for
rescheduling. For the yielding, timeout is calculated for preferable
amount of PCM frames to process. This is an additional merit for
applications, like sound servers. when an I/O thread of the server wait
for the timeout, the other threads can process data frames for server
clients. Furthermore, with usage of rewinding/forwarding, applications
can achieve low latency between transmission position and handling
position even if they uses large size of PCM buffers.
But the timeout should be calculated with enough care of hardware
capabilities. To disable period interrupt, used hardware should satisfy
some requirements for data transmission:
1. Even if drivers don't handle interrupts to queue next data transmission,
hardware voluntarily perform the data transmission when needed
(typically by requesting DMA automatically).
2. hardware has a capability to report current position of data
transmission with enough accuracy against the data transmission.
developers refer this as 'granularity'. If hardware can always
reports updated position after the data transmission finishes, the
granularity equals to the size of period of PCM buffer.
3. a fine size of data transmission in one time. This size is decided
depending on configuration of hardware or DMA controller, but for
efficiency it may not be one byte. Thus some amount of data frame is
transferred by one data transmission. Developers refer this as
'burst-ness'.
The timeout should be calculated according to the item 2 and 3, however
in current ALSA PCM interface supplemental information is not delivered
from drivers to applications. Although at present userspace applications
should be written by a speculative way for this point, there's few
problems because there're a few hardware which satisfy the above items.
However, when more drivers supports this feature, the problem may largely
be exposed and bothers application developers.
This commit adds an option to use 'timer-based scheduling' for data
transmission. This commit adds '--sched-model' option, and the scheduling
mode is enabled when 'timer' is assigned to the option by equal sign.
Although there's some TODOs, you can see the scheduling mode in this
simple program, like:
$ axfer transfer --sched-model=timer -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer --sched-model=timer -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds support of waiter for Linux specific epoll(7) system call.
For portability to the other Unix-like systems such as xBSD, modification
of Makefile.am may be required for conditional build, but this commit
includes no changes for it.
Below lines are examples to use this option:
$ axfer transfer --waiter-type=epoll -M -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer --waiter-type=epoll -M -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds support of waiter for select(2) system call.
Below lines are examples to use this option:
$ axfer transfer --waiter-type=select -M -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer --waiter-type=select -M -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds support of waiter for poll(2) system call.
Below lines are examples to use this option:
$ axfer transfer --waiter-type=poll -M -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer --waiter-type=poll -M -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is an integration to add an option for users to choose waiter
type. Users give the type to value to '--waiter-type' ('-w') option to
choose it. Currently, 'snd_pcm_wait()' is just supported as a default.
This alsa-lib API is implemented with a call of poll(2).
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
There're several types of system calls for multiplexed I/O. They're used to
receive notifications of I/O events. Typically, userspace applications call
them against file descriptor to yield CPU. When I/O is enabled on any of
the descriptors, a task of the application is rescheduled, then the
application execute I/O calls.
This commit adds a common interface for this type of system calls, named as
'waiter'. This is expected to be used with non-blocking file operation and
operations on mapped page frame.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
As of 2017, two userspace library implementations are known; alsa-lib and
tinyalsa. The latter is simple I/O library to use ALSA PCM interface. On
the other hand, alsa-lib is more complicated than it. This is because it's
designed to add features to transmission of data frames; e.g. sample
resampling. To achieve this, alsa-lib has its configuration space and
plugin system.
In aplay, some options are implemented as a flag for the plugins in
alsa-lib. The flag is given to snd_pcm_open(). This commit adds support
for the flags.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In ALSA PCM interface, some parameters are used to configure runtime of
PCM substream independently of actual hardware. These parameters are
mainly used to decide the detailed timing to start/stop PCM substream and
release I/O blocking state of application. These parameters are
represented and delivered by a structure.
In alsa-lib PCM API, the structure is hidden from userspace applications.
The applications can set/get actual parameters by helper functions.
In aplay, three of the parameters are configurable. This commit adds
support for them. When no options are given, default values are used.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In ALSA PCM interface, two parameters are used for size of intermediate
buffer for data frames; period size and buffer size. Actual effects of
these sizes differs depending on hardware, but basically the size of
period is used for intervals of hardware interrupts and the size of buffer
is used to maintain the intermediate buffer as ring buffer. These
parameters can be configured as a part of hardware parameters by
data frame unit or micro second. PCM API in alsa-lib also includes
helper functions to configure them by the two units.
This commit adds support for options to the parameters by both units. When
no options are given, default values are applied according to current
aplay; available maximum size of buffer up to 500msec, a quarter of the
size of buffer for period size. However, these calculation should be
reconsidered somehow.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In aplay, '--test-nowait' is used to suppress calls of snd_pcm_wait()
when I/O operations return -EAGAIN or process truncated number of data
frames. This seems to be for debugging purpose. In this program, this
option is equivalent to suppress event waiting.
This commit adds support for this option.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In alsa-lib PCM API, data frames can be handled in mapped page frame,
instead of calling any system calls.
This commit support for this type of operation. To reduce CPU usage,
this commit uses 'snd_pcm_wait()' to wait for event notification.
Below lines are examples to execute:
$ axfer transfer -M -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer -M -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In alsa-lib PCM API, snd_pcm_read[i|n]() and snd_pcm_write[i|n] can be
used with non-blocking mode. This is available when SND_PCM_NONBLOCK is
used as 'mode' argument for a call of snd_pcm_open().
This commit adds support this type of operation. To reduce CPU usage, this
commit uses 'snd_pcm_wait()' to wait for event notification.
Below lines are examples to execute:
$ axfer transfer -N -P -d 2 -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer -N -C -d 2 -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In aplay, '--fatal-errors' option has an effect to give up recovery of PCM
substream from XRUN state. This commit adds support for this option.
In original implementation, this option brings program abort. This seems
to generate core dump of process VMA. However, typically, XRUN comes from
timing mismatch between hardware and application, therefore core dump has
less helpful. This commit finishes this program in usual way with this
option at XRUN.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In aplay, some options are available to stop data transmission by frame
unit. This commit adds support for the options below:
* --duration (-d)
* For duration seconds. The number of data frames transferred in this
* runtime is calculated by this value and sampling rate.
* --samples (-s)
* For the number of data frames to handle in this runtime.
An original aplay has a similar option; '--max-file-time'. This option
is used for capture data transmission to switch file to write data frame
up to maximum number of frames which container format supports, instead
of terminating. However, this may brings complicated file handling to
this program. To reduce maintaining cost, this option is obsoleted.
Additionally, a handler for SIGUSR1 Unix signal has similar feature to
switch the file. For the same reason, the handler is also obsoleted.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In ALSA PCM interface, before configuring hardware actually, applications
can request available set of hardware parameters for runtime of PCM
substream. The set of parameters are represented and delivered by a
structure.
In alsa-lib PCM API, the above design is abstracted by a series of
snd_pcm_hw_params_xxx() functions. An actual layout of the structure is
hidden from applications by an opaque pointer.
In aplay, '--dump-hw-params' option is for this purpose. With this option,
the command output available set of the hardware parameters.
This commit adds support for the option. Unlike aplay, this commit takes
this program to finish after dumping the parameters for simplicity of
usage.
I note that all of combinations in the set are not necessarily available
when the PCM substream includes dependencies of parameters described by
constraints and rules.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In current aplay, some informative output is available as a default. This
can be suppressed by a quiet option. This commit adds support for it.
An original aplay implementation has no effect of this option in a case
to handle multiple files. However, in a point of usability, this commit
support this case.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In current aplay, default action is to transfer data frames from/to
devices. This commit adds support for this functionality.
Event loop is included in an added file. In the loop, the number of
handled data frames is manipulated by an appropriate way. As a result, users
can stop data transmission frames by frame.
Unlike aplay, when catching SIGSTP, this application performs to suspend
PCM substream. When catching SIGCONT, it performs to resume the PCM
substream. The aim of this design is to avoid XRUN state of the PCM
substream. If users/developers need to any XRUN-recovery test, it's
better to work for the other ways.
Below lines are examples to execute:
$ axfer transfer -P -D hw:0,3 /dev/urandom -f dat -vvv
$ axfer transfer -C -D hw:1,0 /dev/null -r 48000 -vvv
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In alsa-lib PCM API, snd_pcm_read[i|n]() and snd_pcm_write[i|n]() are used
to transfer data frames from/to hardware. When a handler is not opened with
specific flags, these functions perform blocking operation; i.e. the
function call doesn't return till all of request number of data frames are
actually handled, or call is interrupted by Unix signals, or PCM substeam
corrupts due to hardware reasons.
This commit adds support for this type of data transmission. For cases that
requested data frames are not processed by container interface, this commit
adds internal cache mechanism to handle rest of data frames in next timing.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit adds support fo alsa-lib PCM API as a backend of 'xfer'
module. In a set of alsa-lib PCM API, there're two ways to handle data
frames; by calling ioctl(2) with some specific commands with buffer in
user space, or copying data frames on mapped page frames. To support
both ways, this commit adds an operation structure as abstraction.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
In aplay, many command-line options are supported. Some of them have
dependency or conflicts. Furthemore, some of them are just for
runtime configuration of alsa-lib(libasound), and some options can
be used by several xfer backends commonly; e.g. options for file name,
sample format and sampling rate.
This commit adds a parser for the common options below.
* --help (-h)
* Just output 'help' string (not written yet).
* --verbose (-v)
* For verbose output, including information about xfer, mapper and
container.
* --format (-f): string. format literals or one of ['cd'|'cdr'|'dat']
* For sample format supported by ALSA PCM interface. Special format
can be used. For playback, this is auto-detected according to actual
file format.
* --channels (-c)
* For the number of samples included in one data frame. For playback,
this is auto-detected according to actual file format, except for
'raw' format. This option can conflict to above format option.
* --rate (-r)
* For the number of data frames transferred in one second. For playback,
this is auto-detected according to actual file format, except for
'raw' format. This option can conflict to format option above.
* --file-type (-f): string. one of ['wav'|'au'|'voc'|'raw']
* For format of files of given paths. For playback, this is optional
because the format is auto-detected. For capture, this is optional too
because the format is decided according to suffix of given path.
Anyway, this option is used for cases to fail to detect or decide.
* --separate-channels (-I)
* When using several files as source or destination for transmission
of data frame, this option can be used with several file paths.
When '--separate-channels' option is used, users can give several file
paths to source/destination of data transmission, else they can give single
file path for the purpose. When multiple files are handled by this option,
for playback, data frames in first channel is used to construct buffer for
data transmission with multi channel. For capture, data frames in each
channel of buffer are written to each of given path. Furthermore, when a
single path is given for capture, file paths are auto-generated according
to available number of channels. For example, 'name.wav' is given for
2 channels capture, 'name-0.wav' and 'name-1.wav' are generated. In a
case of no suffix, 'name-0' and 'name-1' are generated.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
ALSA has PCM interface to transfer data frames. In userspace, there're
some implementation to utilize this interface to produce application
programming interface; alsa-lib (libasound) and tinyalsa. However, it's
possible to use the interface with raw I/O operations.
This commit adds an common interface to transfer data frames for this
program, named as 'xfer'. This internal interface is designed for users
to select several backend for data transmission. This includes some
functions expected to be called by main program just for data
transmission. In an aspect to maintain PCM substream, suspend feature is
required to handle a pair of SIGTSTP/SIGCONT UNIX signals.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
