Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+===============================
+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.
+