[alsa-devel] [PATCH 13/30] ALSA: doc: ReSTize seq_oss document
Takashi Iwai
tiwai at suse.de
Thu Nov 10 22:06:24 CET 2016
Converted from an ancient plain HTML document. It's much readable now!
Put to designs subdirectory with a slight rename.
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
Documentation/sound/alsa/seq_oss.html | 409 --------------------------------
Documentation/sound/designs/index.rst | 1 +
Documentation/sound/designs/seq-oss.rst | 371 +++++++++++++++++++++++++++++
3 files changed, 372 insertions(+), 409 deletions(-)
delete mode 100644 Documentation/sound/alsa/seq_oss.html
create mode 100644 Documentation/sound/designs/seq-oss.rst
diff --git a/Documentation/sound/alsa/seq_oss.html b/Documentation/sound/alsa/seq_oss.html
deleted file mode 100644
index 9663b45f6fde..000000000000
--- a/Documentation/sound/alsa/seq_oss.html
+++ /dev/null
@@ -1,409 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
-<HTML>
-<HEAD>
- <TITLE>OSS Sequencer Emulation on ALSA</TITLE>
-</HEAD>
-<BODY>
-
-<CENTER>
-<H1>
-
-<HR WIDTH="100%"></H1></CENTER>
-
-<CENTER>
-<H1>
-OSS Sequencer Emulation on ALSA</H1></CENTER>
-
-<HR WIDTH="100%">
-<P>Copyright (c) 1998,1999 by Takashi Iwai
-<TT><A HREF="mailto:iwai at ww.uni-erlangen.de"><iwai at ww.uni-erlangen.de></A></TT>
-<P>ver.0.1.8; Nov. 16, 1999
-<H2>
-
-<HR WIDTH="100%"></H2>
-
-<H2>
-1. Description</H2>
-This directory contains the OSS sequencer emulation driver on ALSA. Note
-that this program is still in the development state.
-<P>What this does - it provides the emulation of the OSS sequencer, access
-via
-<TT>/dev/sequencer</TT> and <TT>/dev/music</TT> devices.
-The most of applications using OSS can run if the appropriate ALSA
-sequencer is prepared.
-<P>The following features are emulated by this driver:
-<UL>
-<LI>
-Normal sequencer and MIDI events:</LI>
-
-<BR>They are converted to the ALSA sequencer events, and sent to the corresponding
-port.
-<LI>
-Timer events:</LI>
-
-<BR>The timer is not selectable by ioctl. The control rate is fixed to
-100 regardless of HZ. That is, even on Alpha system, a tick is always
-1/100 second. The base rate and tempo can be changed in <TT>/dev/music</TT>.
-
-<LI>
-Patch loading:</LI>
-
-<BR>It purely depends on the synth drivers whether it's supported since
-the patch loading is realized by callback to the synth driver.
-<LI>
-I/O controls:</LI>
-
-<BR>Most of controls are accepted. Some controls
-are dependent on the synth driver, as well as even on original OSS.</UL>
-Furthermore, you can find the following advanced features:
-<UL>
-<LI>
-Better queue mechanism:</LI>
-
-<BR>The events are queued before processing them.
-<LI>
-Multiple applications:</LI>
-
-<BR>You can run two or more applications simultaneously (even for OSS sequencer)!
-However, each MIDI device is exclusive - that is, if a MIDI device is opened
-once by some application, other applications can't use it. No such a restriction
-in synth devices.
-<LI>
-Real-time event processing:</LI>
-
-<BR>The events can be processed in real time without using out of bound
-ioctl. To switch to real-time mode, send ABSTIME 0 event. The followed
-events will be processed in real-time without queued. To switch off the
-real-time mode, send RELTIME 0 event.
-<LI>
-<TT>/proc</TT> interface:</LI>
-
-<BR>The status of applications and devices can be shown via <TT>/proc/asound/seq/oss</TT>
-at any time. In the later version, configuration will be changed via <TT>/proc</TT>
-interface, too.</UL>
-
-<H2>
-2. Installation</H2>
-Run configure script with both sequencer support (<TT>--with-sequencer=yes</TT>)
-and OSS emulation (<TT>--with-oss=yes</TT>) options. A module <TT>snd-seq-oss.o</TT>
-will be created. If the synth module of your sound card supports for OSS
-emulation (so far, only Emu8000 driver), this module will be loaded automatically.
-Otherwise, you need to load this module manually.
-<P>At beginning, this module probes all the MIDI ports which have been
-already connected to the sequencer. Once after that, the creation and deletion
-of ports are watched by announcement mechanism of ALSA sequencer.
-<P>The available synth and MIDI devices can be found in proc interface.
-Run "<TT>cat /proc/asound/seq/oss</TT>", and check the devices. For example,
-if you use an AWE64 card, you'll see like the following:
-<PRE> OSS sequencer emulation version 0.1.8
- ALSA client number 63
- ALSA receiver port 0
-
- Number of applications: 0
-
- Number of synth devices: 1
-
- synth 0: [EMU8000]
- type 0x1 : subtype 0x20 : voices 32
- capabilties : ioctl enabled / load_patch enabled
-
- Number of MIDI devices: 3
-
- midi 0: [Emu8000 Port-0] ALSA port 65:0
- capability write / opened none
-
- midi 1: [Emu8000 Port-1] ALSA port 65:1
- capability write / opened none
-
- midi 2: [0: MPU-401 (UART)] ALSA port 64:0
- capability read/write / opened none</PRE>
-Note that the device number may be different from the information of
-<TT>/proc/asound/oss-devices</TT>
-or ones of the original OSS driver. Use the device number listed in <TT>/proc/asound/seq/oss</TT>
-to play via OSS sequencer emulation.
-<H2>
-3. Using Synthesizer Devices</H2>
-Run your favorite program. I've tested playmidi-2.4, awemidi-0.4.3, gmod-3.1
-and xmp-1.1.5. You can load samples via <TT>/dev/sequencer</TT> like sfxload,
-too.
-<P>If the lowlevel driver supports multiple access to synth devices (like
-Emu8000 driver), two or more applications are allowed to run at the same
-time.
-<H2>
-4. Using MIDI Devices</H2>
-So far, only MIDI output was tested. MIDI input was not checked at all,
-but hopefully it will work. Use the device number listed in <TT>/proc/asound/seq/oss</TT>.
-Be aware that these numbers are mostly different from the list in
-<TT>/proc/asound/oss-devices</TT>.
-<H2>
-5. Module Options</H2>
-The following module options are available:
-<UL>
-<LI>
-<TT>maxqlen</TT></LI>
-
-<BR>specifies the maximum read/write queue length. This queue is private
-for OSS sequencer, so that it is independent from the queue length of ALSA
-sequencer. Default value is 1024.
-<LI>
-<TT>seq_oss_debug</TT></LI>
-
-<BR>specifies the debug level and accepts zero (= no debug message) or
-positive integer. Default value is 0.</UL>
-
-<H2>
-6. Queue Mechanism</H2>
-OSS sequencer emulation uses an ALSA priority queue. The
-events from <TT>/dev/sequencer</TT> are processed and put onto the queue
-specified by module option.
-<P>All the events from <TT>/dev/sequencer</TT> are parsed at beginning.
-The timing events are also parsed at this moment, so that the events may
-be processed in real-time. Sending an event ABSTIME 0 switches the operation
-mode to real-time mode, and sending an event RELTIME 0 switches it off.
-In the real-time mode, all events are dispatched immediately.
-<P>The queued events are dispatched to the corresponding ALSA sequencer
-ports after scheduled time by ALSA sequencer dispatcher.
-<P>If the write-queue is full, the application sleeps until a certain amount
-(as default one half) becomes empty in blocking mode. The synchronization
-to write timing was implemented, too.
-<P>The input from MIDI devices or echo-back events are stored on read FIFO
-queue. If application reads <TT>/dev/sequencer</TT> in blocking mode, the
-process will be awaked.
-
-<H2>
-7. Interface to Synthesizer Device</H2>
-
-<H3>
-7.1. Registration</H3>
-To register an OSS synthesizer device, use <TT>snd_seq_oss_synth_register</TT>
-function.
-<PRE>int snd_seq_oss_synth_register(char *name, int type, int subtype, int nvoices,
- snd_seq_oss_callback_t *oper, void *private_data)</PRE>
-The arguments <TT>name</TT>, <TT>type</TT>, <TT>subtype</TT> and
-<TT>nvoices</TT>
-are used for making the appropriate synth_info structure for ioctl. The
-return value is an index number of this device. This index must be remembered
-for unregister. If registration is failed, -errno will be returned.
-<P>To release this device, call <TT>snd_seq_oss_synth_unregister function</TT>:
-<PRE>int snd_seq_oss_synth_unregister(int index),</PRE>
-where the <TT>index</TT> is the index number returned by register function.
-<H3>
-7.2. Callbacks</H3>
-OSS synthesizer devices have capability for sample downloading and ioctls
-like sample reset. In OSS emulation, these special features are realized
-by using callbacks. The registration argument oper is used to specify these
-callbacks. The following callback functions must be defined:
-<PRE>snd_seq_oss_callback_t:
- int (*open)(snd_seq_oss_arg_t *p, void *closure);
- int (*close)(snd_seq_oss_arg_t *p);
- int (*ioctl)(snd_seq_oss_arg_t *p, unsigned int cmd, unsigned long arg);
- int (*load_patch)(snd_seq_oss_arg_t *p, int format, const char *buf, int offs, int count);
- int (*reset)(snd_seq_oss_arg_t *p);
-Except for <TT>open</TT> and <TT>close</TT> callbacks, they are allowed
-to be NULL.
-<P>Each callback function takes the argument type snd_seq_oss_arg_t as the
-first argument.
-<PRE>struct snd_seq_oss_arg_t {
- int app_index;
- int file_mode;
- int seq_mode;
- snd_seq_addr_t addr;
- void *private_data;
- int event_passing;
-};</PRE>
-The first three fields, <TT>app_index</TT>, <TT>file_mode</TT> and
-<TT>seq_mode</TT>
-are initialized by OSS sequencer. The <TT>app_index</TT> is the application
-index which is unique to each application opening OSS sequencer. The
-<TT>file_mode</TT>
-is bit-flags indicating the file operation mode. See
-<TT>seq_oss.h</TT>
-for its meaning. The <TT>seq_mode</TT> is sequencer operation mode. In
-the current version, only <TT>SND_OSSSEQ_MODE_SYNTH</TT> is used.
-<P>The next two fields, <TT>addr</TT> and <TT>private_data</TT>, must be
-filled by the synth driver at open callback. The <TT>addr</TT> contains
-the address of ALSA sequencer port which is assigned to this device. If
-the driver allocates memory for <TT>private_data</TT>, it must be released
-in close callback by itself.
-<P>The last field, <TT>event_passing</TT>, indicates how to translate note-on
-/ off events. In <TT>PROCESS_EVENTS</TT> mode, the note 255 is regarded
-as velocity change, and key pressure event is passed to the port. In <TT>PASS_EVENTS</TT>
-mode, all note on/off events are passed to the port without modified. <TT>PROCESS_KEYPRESS</TT>
-mode checks the note above 128 and regards it as key pressure event (mainly
-for Emu8000 driver).
-<H4>
-7.2.1. Open Callback</H4>
-The <TT>open</TT> is called at each time this device is opened by an application
-using OSS sequencer. This must not be NULL. Typically, the open callback
-does the following procedure:
-<OL>
-<LI>
-Allocate private data record.</LI>
-
-<LI>
-Create an ALSA sequencer port.</LI>
-
-<LI>
-Set the new port address on arg->addr.</LI>
-
-<LI>
-Set the private data record pointer on arg->private_data.</LI>
-</OL>
-Note that the type bit-flags in port_info of this synth port must NOT contain
-<TT>TYPE_MIDI_GENERIC</TT>
-bit. Instead, <TT>TYPE_SPECIFIC</TT> should be used. Also, <TT>CAP_SUBSCRIPTION</TT>
-bit should NOT be included, too. This is necessary to tell it from other
-normal MIDI devices. If the open procedure succeeded, return zero. Otherwise,
-return -errno.
-<H4>
-7.2.2 Ioctl Callback</H4>
-The <TT>ioctl</TT> callback is called when the sequencer receives device-specific
-ioctls. The following two ioctls should be processed by this callback:
-<UL>
-<LI>
-<TT>IOCTL_SEQ_RESET_SAMPLES</TT></LI>
-
-<BR>reset all samples on memory -- return 0
-<LI>
-<TT>IOCTL_SYNTH_MEMAVL</TT></LI>
-
-<BR>return the available memory size
-<LI>
-<TT>FM_4OP_ENABLE</TT></LI>
-
-<BR>can be ignored usually</UL>
-The other ioctls are processed inside the sequencer without passing to
-the lowlevel driver.
-<H4>
-7.2.3 Load_Patch Callback</H4>
-The <TT>load_patch</TT> callback is used for sample-downloading. This callback
-must read the data on user-space and transfer to each device. Return 0
-if succeeded, and -errno if failed. The format argument is the patch key
-in patch_info record. The buf is user-space pointer where patch_info record
-is stored. The offs can be ignored. The count is total data size of this
-sample data.
-<H4>
-7.2.4 Close Callback</H4>
-The <TT>close</TT> callback is called when this device is closed by the
-application. If any private data was allocated in open callback, it must
-be released in the close callback. The deletion of ALSA port should be
-done here, too. This callback must not be NULL.
-<H4>
-7.2.5 Reset Callback</H4>
-The <TT>reset</TT> callback is called when sequencer device is reset or
-closed by applications. The callback should turn off the sounds on the
-relevant port immediately, and initialize the status of the port. If this
-callback is undefined, OSS seq sends a <TT>HEARTBEAT</TT> event to the
-port.
-<H3>
-7.3 Events</H3>
-Most of the events are processed by sequencer and translated to the adequate
-ALSA sequencer events, so that each synth device can receive by input_event
-callback of ALSA sequencer port. The following ALSA events should be implemented
-by the driver:
-<BR>
-<TABLE BORDER WIDTH="75%" NOSAVE >
-<TR NOSAVE>
-<TD NOSAVE><B>ALSA event</B></TD>
-
-<TD><B>Original OSS events</B></TD>
-</TR>
-
-<TR>
-<TD>NOTEON</TD>
-
-<TD>SEQ_NOTEON
-<BR>MIDI_NOTEON</TD>
-</TR>
-
-<TR>
-<TD>NOTE</TD>
-
-<TD>SEQ_NOTEOFF
-<BR>MIDI_NOTEOFF</TD>
-</TR>
-
-<TR NOSAVE>
-<TD NOSAVE>KEYPRESS</TD>
-
-<TD>MIDI_KEY_PRESSURE</TD>
-</TR>
-
-<TR NOSAVE>
-<TD>CHANPRESS</TD>
-
-<TD NOSAVE>SEQ_AFTERTOUCH
-<BR>MIDI_CHN_PRESSURE</TD>
-</TR>
-
-<TR NOSAVE>
-<TD NOSAVE>PGMCHANGE</TD>
-
-<TD NOSAVE>SEQ_PGMCHANGE
-<BR>MIDI_PGM_CHANGE</TD>
-</TR>
-
-<TR>
-<TD>PITCHBEND</TD>
-
-<TD>SEQ_CONTROLLER(CTRL_PITCH_BENDER)
-<BR>MIDI_PITCH_BEND</TD>
-</TR>
-
-<TR>
-<TD>CONTROLLER</TD>
-
-<TD>MIDI_CTL_CHANGE
-<BR>SEQ_BALANCE (with CTL_PAN)</TD>
-</TR>
-
-<TR>
-<TD>CONTROL14</TD>
-
-<TD>SEQ_CONTROLLER</TD>
-</TR>
-
-<TR>
-<TD>REGPARAM</TD>
-
-<TD>SEQ_CONTROLLER(CTRL_PITCH_BENDER_RANGE)</TD>
-</TR>
-
-<TR>
-<TD>SYSEX</TD>
-
-<TD>SEQ_SYSEX</TD>
-</TR>
-</TABLE>
-
-<P>The most of these behavior can be realized by MIDI emulation driver
-included in the Emu8000 lowlevel driver. In the future release, this module
-will be independent.
-<P>Some OSS events (<TT>SEQ_PRIVATE</TT> and <TT>SEQ_VOLUME</TT> events) are passed as event
-type SND_SEQ_OSS_PRIVATE. The OSS sequencer passes these event 8 byte
-packets without any modification. The lowlevel driver should process these
-events appropriately.
-<H2>
-8. Interface to MIDI Device</H2>
-Since the OSS emulation probes the creation and deletion of ALSA MIDI sequencer
-ports automatically by receiving announcement from ALSA sequencer, the
-MIDI devices don't need to be registered explicitly like synth devices.
-However, the MIDI port_info registered to ALSA sequencer must include a group
-name <TT>SND_SEQ_GROUP_DEVICE</TT> and a capability-bit <TT>CAP_READ</TT> or
-<TT>CAP_WRITE</TT>. Also, subscription capabilities, <TT>CAP_SUBS_READ</TT> or <TT>CAP_SUBS_WRITE</TT>,
-must be defined, too. If these conditions are not satisfied, the port is not
-registered as OSS sequencer MIDI device.
-<P>The events via MIDI devices are parsed in OSS sequencer and converted
-to the corresponding ALSA sequencer events. The input from MIDI sequencer
-is also converted to MIDI byte events by OSS sequencer. This works just
-a reverse way of seq_midi module.
-<H2>
-9. Known Problems / TODO's</H2>
-
-<UL>
-<LI>
-Patch loading via ALSA instrument layer is not implemented yet.</LI>
-</UL>
-
-</BODY>
-</HTML>
diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index 5b3033c556d0..0ca3a6b0a5ce 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -8,3 +8,4 @@ Designs and Implementations
procfile
powersave
oss-emulation
+ seq-oss
diff --git a/Documentation/sound/designs/seq-oss.rst b/Documentation/sound/designs/seq-oss.rst
new file mode 100644
index 000000000000..e82ffe0e7f43
--- /dev/null
+++ b/Documentation/sound/designs/seq-oss.rst
@@ -0,0 +1,371 @@
+===============================
+OSS Sequencer Emulation on ALSA
+===============================
+
+Copyright (c) 1998,1999 by Takashi Iwai
+
+ver.0.1.8; Nov. 16, 1999
+
+Description
+===========
+
+This directory contains the OSS sequencer emulation driver on ALSA. Note
+that this program is still in the development state.
+
+What this does - it provides the emulation of the OSS sequencer, access
+via ``/dev/sequencer`` and ``/dev/music`` devices.
+The most of applications using OSS can run if the appropriate ALSA
+sequencer is prepared.
+
+The following features are emulated by this driver:
+
+* Normal sequencer and MIDI events:
+
+ They are converted to the ALSA sequencer events, and sent to the
+ corresponding port.
+
+* Timer events:
+
+ The timer is not selectable by ioctl. The control rate is fixed to
+ 100 regardless of HZ. That is, even on Alpha system, a tick is always
+ 1/100 second. The base rate and tempo can be changed in ``/dev/music``.
+
+* Patch loading:
+
+ It purely depends on the synth drivers whether it's supported since
+ the patch loading is realized by callback to the synth driver.
+
+* I/O controls:
+
+ Most of controls are accepted. Some controls
+ are dependent on the synth driver, as well as even on original OSS.
+
+Furthermore, you can find the following advanced features:
+
+* Better queue mechanism:
+
+ The events are queued before processing them.
+
+* Multiple applications:
+
+ You can run two or more applications simultaneously (even for OSS
+ sequencer)!
+ However, each MIDI device is exclusive - that is, if a MIDI device
+ is opened once by some application, other applications can't use
+ it. No such a restriction in synth devices.
+
+* Real-time event processing:
+
+ The events can be processed in real time without using out of bound
+ ioctl. To switch to real-time mode, send ABSTIME 0 event. The followed
+ events will be processed in real-time without queued. To switch off the
+ real-time mode, send RELTIME 0 event.
+
+* ``/proc`` interface:
+
+ The status of applications and devices can be shown via
+ ``/proc/asound/seq/oss`` at any time. In the later version,
+ configuration will be changed via ``/proc`` interface, too.
+
+
+Installation
+============
+
+Run configure script with both sequencer support (``--with-sequencer=yes``)
+and OSS emulation (``--with-oss=yes``) options. A module ``snd-seq-oss.o``
+will be created. If the synth module of your sound card supports for OSS
+emulation (so far, only Emu8000 driver), this module will be loaded
+automatically.
+Otherwise, you need to load this module manually.
+
+At beginning, this module probes all the MIDI ports which have been
+already connected to the sequencer. Once after that, the creation and deletion
+of ports are watched by announcement mechanism of ALSA sequencer.
+
+The available synth and MIDI devices can be found in proc interface.
+Run ``cat /proc/asound/seq/oss``, and check the devices. For example,
+if you use an AWE64 card, you'll see like the following:
+::
+
+ OSS sequencer emulation version 0.1.8
+ ALSA client number 63
+ ALSA receiver port 0
+
+ Number of applications: 0
+
+ Number of synth devices: 1
+ synth 0: [EMU8000]
+ type 0x1 : subtype 0x20 : voices 32
+ capabilties : ioctl enabled / load_patch enabled
+
+ Number of MIDI devices: 3
+ midi 0: [Emu8000 Port-0] ALSA port 65:0
+ capability write / opened none
+
+ midi 1: [Emu8000 Port-1] ALSA port 65:1
+ capability write / opened none
+
+ midi 2: [0: MPU-401 (UART)] ALSA port 64:0
+ capability read/write / opened none
+
+Note that the device number may be different from the information of
+``/proc/asound/oss-devices`` or ones of the original OSS driver.
+Use the device number listed in ``/proc/asound/seq/oss``
+to play via OSS sequencer emulation.
+
+Using Synthesizer Devices
+=========================
+
+Run your favorite program. I've tested playmidi-2.4, awemidi-0.4.3, gmod-3.1
+and xmp-1.1.5. You can load samples via ``/dev/sequencer`` like sfxload,
+too.
+
+If the lowlevel driver supports multiple access to synth devices (like
+Emu8000 driver), two or more applications are allowed to run at the same
+time.
+
+Using MIDI Devices
+==================
+
+So far, only MIDI output was tested. MIDI input was not checked at all,
+but hopefully it will work. Use the device number listed in
+``/proc/asound/seq/oss``.
+Be aware that these numbers are mostly different from the list in
+``/proc/asound/oss-devices``.
+
+Module Options
+==============
+
+The following module options are available:
+
+maxqlen
+ specifies the maximum read/write queue length. This queue is private
+ for OSS sequencer, so that it is independent from the queue length of ALSA
+ sequencer. Default value is 1024.
+
+seq_oss_debug
+ specifies the debug level and accepts zero (= no debug message) or
+ positive integer. Default value is 0.
+
+Queue Mechanism
+===============
+
+OSS sequencer emulation uses an ALSA priority queue. The
+events from ``/dev/sequencer`` are processed and put onto the queue
+specified by module option.
+
+All the events from ``/dev/sequencer`` are parsed at beginning.
+The timing events are also parsed at this moment, so that the events may
+be processed in real-time. Sending an event ABSTIME 0 switches the operation
+mode to real-time mode, and sending an event RELTIME 0 switches it off.
+In the real-time mode, all events are dispatched immediately.
+
+The queued events are dispatched to the corresponding ALSA sequencer
+ports after scheduled time by ALSA sequencer dispatcher.
+
+If the write-queue is full, the application sleeps until a certain amount
+(as default one half) becomes empty in blocking mode. The synchronization
+to write timing was implemented, too.
+
+The input from MIDI devices or echo-back events are stored on read FIFO
+queue. If application reads ``/dev/sequencer`` in blocking mode, the
+process will be awaked.
+
+Interface to Synthesizer Device
+===============================
+
+Registration
+------------
+
+To register an OSS synthesizer device, use snd_seq_oss_synth_register()
+function:
+::
+
+ int snd_seq_oss_synth_register(char *name, int type, int subtype, int nvoices,
+ snd_seq_oss_callback_t *oper, void *private_data)
+
+The arguments ``name``, ``type``, ``subtype`` and ``nvoices``
+are used for making the appropriate synth_info structure for ioctl. The
+return value is an index number of this device. This index must be remembered
+for unregister. If registration is failed, -errno will be returned.
+
+To release this device, call snd_seq_oss_synth_unregister() function:
+::
+
+ int snd_seq_oss_synth_unregister(int index)
+
+where the ``index`` is the index number returned by register function.
+
+Callbacks
+---------
+
+OSS synthesizer devices have capability for sample downloading and ioctls
+like sample reset. In OSS emulation, these special features are realized
+by using callbacks. The registration argument oper is used to specify these
+callbacks. The following callback functions must be defined:
+::
+
+ snd_seq_oss_callback_t:
+ int (*open)(snd_seq_oss_arg_t *p, void *closure);
+ int (*close)(snd_seq_oss_arg_t *p);
+ int (*ioctl)(snd_seq_oss_arg_t *p, unsigned int cmd, unsigned long arg);
+ int (*load_patch)(snd_seq_oss_arg_t *p, int format, const char *buf, int offs, int count);
+ int (*reset)(snd_seq_oss_arg_t *p);
+
+Except for ``open`` and ``close`` callbacks, they are allowed to be NULL.
+
+Each callback function takes the argument type ``snd_seq_oss_arg_t`` as the
+first argument.
+::
+
+ struct snd_seq_oss_arg_t {
+ int app_index;
+ int file_mode;
+ int seq_mode;
+ snd_seq_addr_t addr;
+ void *private_data;
+ int event_passing;
+ };
+
+The first three fields, ``app_index``, ``file_mode`` and ``seq_mode``
+are initialized by OSS sequencer. The ``app_index`` is the application
+index which is unique to each application opening OSS sequencer. The
+``file_mode`` is bit-flags indicating the file operation mode. See
+``seq_oss.h`` for its meaning. The ``seq_mode`` is sequencer operation
+mode. In the current version, only ``SND_OSSSEQ_MODE_SYNTH`` is used.
+
+The next two fields, ``addr`` and ``private_data``, must be
+filled by the synth driver at open callback. The ``addr`` contains
+the address of ALSA sequencer port which is assigned to this device. If
+the driver allocates memory for ``private_data``, it must be released
+in close callback by itself.
+
+The last field, ``event_passing``, indicates how to translate note-on
+/ off events. In ``PROCESS_EVENTS`` mode, the note 255 is regarded
+as velocity change, and key pressure event is passed to the port. In
+``PASS_EVENTS`` mode, all note on/off events are passed to the port
+without modified. ``PROCESS_KEYPRESS`` mode checks the note above 128
+and regards it as key pressure event (mainly for Emu8000 driver).
+
+Open Callback
+-------------
+
+The ``open`` is called at each time this device is opened by an application
+using OSS sequencer. This must not be NULL. Typically, the open callback
+does the following procedure:
+
+#. Allocate private data record.
+#. Create an ALSA sequencer port.
+#. Set the new port address on ``arg->addr``.
+#. Set the private data record pointer on ``arg->private_data``.
+
+Note that the type bit-flags in port_info of this synth port must NOT contain
+``TYPE_MIDI_GENERIC``
+bit. Instead, ``TYPE_SPECIFIC`` should be used. Also, ``CAP_SUBSCRIPTION``
+bit should NOT be included, too. This is necessary to tell it from other
+normal MIDI devices. If the open procedure succeeded, return zero. Otherwise,
+return -errno.
+
+Ioctl Callback
+--------------
+
+The ``ioctl`` callback is called when the sequencer receives device-specific
+ioctls. The following two ioctls should be processed by this callback:
+
+IOCTL_SEQ_RESET_SAMPLES
+ reset all samples on memory -- return 0
+
+IOCTL_SYNTH_MEMAVL
+ return the available memory size
+
+FM_4OP_ENABLE
+ can be ignored usually
+
+The other ioctls are processed inside the sequencer without passing to
+the lowlevel driver.
+
+Load_Patch Callback
+-------------------
+
+The ``load_patch`` callback is used for sample-downloading. This callback
+must read the data on user-space and transfer to each device. Return 0
+if succeeded, and -errno if failed. The format argument is the patch key
+in patch_info record. The buf is user-space pointer where patch_info record
+is stored. The offs can be ignored. The count is total data size of this
+sample data.
+
+Close Callback
+--------------
+
+The ``close`` callback is called when this device is closed by the
+application. If any private data was allocated in open callback, it must
+be released in the close callback. The deletion of ALSA port should be
+done here, too. This callback must not be NULL.
+
+Reset Callback
+--------------
+
+The ``reset`` callback is called when sequencer device is reset or
+closed by applications. The callback should turn off the sounds on the
+relevant port immediately, and initialize the status of the port. If this
+callback is undefined, OSS seq sends a ``HEARTBEAT`` event to the
+port.
+
+Events
+======
+
+Most of the events are processed by sequencer and translated to the adequate
+ALSA sequencer events, so that each synth device can receive by input_event
+callback of ALSA sequencer port. The following ALSA events should be
+implemented by the driver:
+
+============= ===================
+ALSA event Original OSS events
+============= ===================
+NOTEON SEQ_NOTEON, MIDI_NOTEON
+NOTE SEQ_NOTEOFF, MIDI_NOTEOFF
+KEYPRESS MIDI_KEY_PRESSURE
+CHANPRESS SEQ_AFTERTOUCH, MIDI_CHN_PRESSURE
+PGMCHANGE SEQ_PGMCHANGE, MIDI_PGM_CHANGE
+PITCHBEND SEQ_CONTROLLER(CTRL_PITCH_BENDER),
+ MIDI_PITCH_BEND
+CONTROLLER MIDI_CTL_CHANGE,
+ SEQ_BALANCE (with CTL_PAN)
+CONTROL14 SEQ_CONTROLLER
+REGPARAM SEQ_CONTROLLER(CTRL_PITCH_BENDER_RANGE)
+SYSEX SEQ_SYSEX
+============= ===================
+
+The most of these behavior can be realized by MIDI emulation driver
+included in the Emu8000 lowlevel driver. In the future release, this module
+will be independent.
+
+Some OSS events (``SEQ_PRIVATE`` and ``SEQ_VOLUME`` events) are passed as event
+type SND_SEQ_OSS_PRIVATE. The OSS sequencer passes these event 8 byte
+packets without any modification. The lowlevel driver should process these
+events appropriately.
+
+Interface to MIDI Device
+========================
+
+Since the OSS emulation probes the creation and deletion of ALSA MIDI
+sequencer ports automatically by receiving announcement from ALSA
+sequencer, the MIDI devices don't need to be registered explicitly
+like synth devices.
+However, the MIDI port_info registered to ALSA sequencer must include
+a group name ``SND_SEQ_GROUP_DEVICE`` and a capability-bit
+``CAP_READ`` or ``CAP_WRITE``. Also, subscription capabilities,
+``CAP_SUBS_READ`` or ``CAP_SUBS_WRITE``, must be defined, too. If
+these conditions are not satisfied, the port is not registered as OSS
+sequencer MIDI device.
+
+The events via MIDI devices are parsed in OSS sequencer and converted
+to the corresponding ALSA sequencer events. The input from MIDI sequencer
+is also converted to MIDI byte events by OSS sequencer. This works just
+a reverse way of seq_midi module.
+
+Known Problems / TODO's
+=======================
+
+* Patch loading via ALSA instrument layer is not implemented yet.
+
--
2.10.2
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