diff options
| author | Takashi Iwai <tiwai@suse.de> | 2016-11-09 16:46:02 +0100 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2016-11-10 18:09:27 +0100 |
| commit | 07aecc06eb32ff0010dff69438806b6f200fc1fd (patch) | |
| tree | 53c323ea8efa0890afa78b10f34df8af67f2dee9 | |
| parent | 0c266c4b707e263ac74e0bd4330b4193fa46c434 (diff) | |
ALSA: doc: ReSTize seq_oss document
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@suse.de>
| -rw-r--r-- | Documentation/sound/alsa/seq_oss.html | 409 | ||||
| -rw-r--r-- | Documentation/sound/designs/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/sound/designs/seq-oss.rst | 371 |
3 files changed, 372 insertions, 409 deletions
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@ww.uni-erlangen.de"><iwai@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. + |