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