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4 <TITLE>OSS Sequencer Emulation on ALSA</TITLE>
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15 OSS Sequencer Emulation on ALSA</H1></CENTER>
18 <P>Copyright (c) 1998,1999 by Takashi Iwai
19 <TT><A HREF="mailto:iwai@ww.uni-erlangen.de"><iwai@ww.uni-erlangen.de></A></TT>
20 <P>ver.0.1.8; Nov. 16, 1999
23 <HR WIDTH="100%"></H2>
27 This directory contains the OSS sequencer emulation driver on ALSA. Note
28 that this program is still in the development state.
29 <P>What this does - it provides the emulation of the OSS sequencer, access
31 <TT>/dev/sequencer</TT> and <TT>/dev/music</TT> devices.
32 The most of applications using OSS can run if the appropriate ALSA
33 sequencer is prepared.
34 <P>The following features are emulated by this driver:
37 Normal sequencer and MIDI events:</LI>
39 <BR>They are converted to the ALSA sequencer events, and sent to the corresponding
44 <BR>The timer is not selectable by ioctl. The control rate is fixed to
45 100 regardless of HZ. That is, even on Alpha system, a tick is always
46 1/100 second. The base rate and tempo can be changed in <TT>/dev/music</TT>.
51 <BR>It purely depends on the synth drivers whether it's supported since
52 the patch loading is realized by callback to the synth driver.
56 <BR>Most of controls are accepted. Some controls
57 are dependent on the synth driver, as well as even on original OSS.</UL>
58 Furthermore, you can find the following advanced features:
61 Better queue mechanism:</LI>
63 <BR>The events are queued before processing them.
65 Multiple applications:</LI>
67 <BR>You can run two or more applications simultaneously (even for OSS sequencer)!
68 However, each MIDI device is exclusive - that is, if a MIDI device is opened
69 once by some application, other applications can't use it. No such a restriction
72 Real-time event processing:</LI>
74 <BR>The events can be processed in real time without using out of bound
75 ioctl. To switch to real-time mode, send ABSTIME 0 event. The followed
76 events will be processed in real-time without queued. To switch off the
77 real-time mode, send RELTIME 0 event.
79 <TT>/proc</TT> interface:</LI>
81 <BR>The status of applications and devices can be shown via <TT>/proc/asound/seq/oss</TT>
82 at any time. In the later version, configuration will be changed via <TT>/proc</TT>
87 Run configure script with both sequencer support (<TT>--with-sequencer=yes</TT>)
88 and OSS emulation (<TT>--with-oss=yes</TT>) options. A module <TT>snd-seq-oss.o</TT>
89 will be created. If the synth module of your sound card supports for OSS
90 emulation (so far, only Emu8000 driver), this module will be loaded automatically.
91 Otherwise, you need to load this module manually.
92 <P>At beginning, this module probes all the MIDI ports which have been
93 already connected to the sequencer. Once after that, the creation and deletion
94 of ports are watched by announcement mechanism of ALSA sequencer.
95 <P>The available synth and MIDI devices can be found in proc interface.
96 Run "<TT>cat /proc/asound/seq/oss</TT>", and check the devices. For example,
97 if you use an AWE64 card, you'll see like the following:
98 <PRE> OSS sequencer emulation version 0.1.8
99 ALSA client number 63
100 ALSA receiver port 0
102 Number of applications: 0
104 Number of synth devices: 1
106 synth 0: [EMU8000]
107 type 0x1 : subtype 0x20 : voices 32
108 capabilties : ioctl enabled / load_patch enabled
110 Number of MIDI devices: 3
112 midi 0: [Emu8000 Port-0] ALSA port 65:0
113 capability write / opened none
115 midi 1: [Emu8000 Port-1] ALSA port 65:1
116 capability write / opened none
118 midi 2: [0: MPU-401 (UART)] ALSA port 64:0
119 capability read/write / opened none</PRE>
120 Note that the device number may be different from the information of
121 <TT>/proc/asound/oss-devices</TT>
122 or ones of the original OSS driver. Use the device number listed in <TT>/proc/asound/seq/oss</TT>
123 to play via OSS sequencer emulation.
125 3. Using Synthesizer Devices</H2>
126 Run your favorite program. I've tested playmidi-2.4, awemidi-0.4.3, gmod-3.1
127 and xmp-1.1.5. You can load samples via <TT>/dev/sequencer</TT> like sfxload,
129 <P>If the lowlevel driver supports multiple access to synth devices (like
130 Emu8000 driver), two or more applications are allowed to run at the same
133 4. Using MIDI Devices</H2>
134 So far, only MIDI output was tested. MIDI input was not checked at all,
135 but hopefully it will work. Use the device number listed in <TT>/proc/asound/seq/oss</TT>.
136 Be aware that these numbers are mostly different from the list in
137 <TT>/proc/asound/oss-devices</TT>.
139 5. Module Options</H2>
140 The following module options are available:
143 <TT>maxqlen</TT></LI>
145 <BR>specifies the maximum read/write queue length. This queue is private
146 for OSS sequencer, so that it is independent from the queue length of ALSA
147 sequencer. Default value is 1024.
149 <TT>seq_oss_debug</TT></LI>
151 <BR>specifies the debug level and accepts zero (= no debug message) or
152 positive integer. Default value is 0.</UL>
155 6. Queue Mechanism</H2>
156 OSS sequencer emulation uses an ALSA priority queue. The
157 events from <TT>/dev/sequencer</TT> are processed and put onto the queue
158 specified by module option.
159 <P>All the events from <TT>/dev/sequencer</TT> are parsed at beginning.
160 The timing events are also parsed at this moment, so that the events may
161 be processed in real-time. Sending an event ABSTIME 0 switches the operation
162 mode to real-time mode, and sending an event RELTIME 0 switches it off.
163 In the real-time mode, all events are dispatched immediately.
164 <P>The queued events are dispatched to the corresponding ALSA sequencer
165 ports after scheduled time by ALSA sequencer dispatcher.
166 <P>If the write-queue is full, the application sleeps until a certain amount
167 (as default one half) becomes empty in blocking mode. The synchronization
168 to write timing was implemented, too.
169 <P>The input from MIDI devices or echo-back events are stored on read FIFO
170 queue. If application reads <TT>/dev/sequencer</TT> in blocking mode, the
171 process will be awaked.
174 7. Interface to Synthesizer Device</H2>
177 7.1. Registration</H3>
178 To register an OSS synthesizer device, use <TT>snd_seq_oss_synth_register</TT>
180 <PRE>int snd_seq_oss_synth_register(char *name, int type, int subtype, int nvoices,
181 snd_seq_oss_callback_t *oper, void *private_data)</PRE>
182 The arguments <TT>name</TT>, <TT>type</TT>, <TT>subtype</TT> and
184 are used for making the appropriate synth_info structure for ioctl. The
185 return value is an index number of this device. This index must be remembered
186 for unregister. If registration is failed, -errno will be returned.
187 <P>To release this device, call <TT>snd_seq_oss_synth_unregister function</TT>:
188 <PRE>int snd_seq_oss_synth_unregister(int index),</PRE>
189 where the <TT>index</TT> is the index number returned by register function.
192 OSS synthesizer devices have capability for sample downloading and ioctls
193 like sample reset. In OSS emulation, these special features are realized
194 by using callbacks. The registration argument oper is used to specify these
195 callbacks. The following callback functions must be defined:
196 <PRE>snd_seq_oss_callback_t:
197 int (*open)(snd_seq_oss_arg_t *p, void *closure);
198 int (*close)(snd_seq_oss_arg_t *p);
199 int (*ioctl)(snd_seq_oss_arg_t *p, unsigned int cmd, unsigned long arg);
200 int (*load_patch)(snd_seq_oss_arg_t *p, int format, const char *buf, int offs, int count);
201 int (*reset)(snd_seq_oss_arg_t *p);
202 Except for <TT>open</TT> and <TT>close</TT> callbacks, they are allowed
204 <P>Each callback function takes the argument type snd_seq_oss_arg_t as the
206 <PRE>struct snd_seq_oss_arg_t {
207 int app_index;
208 int file_mode;
209 int seq_mode;
210 snd_seq_addr_t addr;
211 void *private_data;
212 int event_passing;
214 The first three fields, <TT>app_index</TT>, <TT>file_mode</TT> and
216 are initialized by OSS sequencer. The <TT>app_index</TT> is the application
217 index which is unique to each application opening OSS sequencer. The
219 is bit-flags indicating the file operation mode. See
221 for its meaning. The <TT>seq_mode</TT> is sequencer operation mode. In
222 the current version, only <TT>SND_OSSSEQ_MODE_SYNTH</TT> is used.
223 <P>The next two fields, <TT>addr</TT> and <TT>private_data</TT>, must be
224 filled by the synth driver at open callback. The <TT>addr</TT> contains
225 the address of ALSA sequencer port which is assigned to this device. If
226 the driver allocates memory for <TT>private_data</TT>, it must be released
227 in close callback by itself.
228 <P>The last field, <TT>event_passing</TT>, indicates how to translate note-on
229 / off events. In <TT>PROCESS_EVENTS</TT> mode, the note 255 is regarded
230 as velocity change, and key pressure event is passed to the port. In <TT>PASS_EVENTS</TT>
231 mode, all note on/off events are passed to the port without modified. <TT>PROCESS_KEYPRESS</TT>
232 mode checks the note above 128 and regards it as key pressure event (mainly
235 7.2.1. Open Callback</H4>
236 The <TT>open</TT> is called at each time this device is opened by an application
237 using OSS sequencer. This must not be NULL. Typically, the open callback
238 does the following procedure:
241 Allocate private data record.</LI>
244 Create an ALSA sequencer port.</LI>
247 Set the new port address on arg->addr.</LI>
250 Set the private data record pointer on arg->private_data.</LI>
252 Note that the type bit-flags in port_info of this synth port must NOT contain
253 <TT>TYPE_MIDI_GENERIC</TT>
254 bit. Instead, <TT>TYPE_SPECIFIC</TT> should be used. Also, <TT>CAP_SUBSCRIPTION</TT>
255 bit should NOT be included, too. This is necessary to tell it from other
256 normal MIDI devices. If the open procedure succeeded, return zero. Otherwise,
259 7.2.2 Ioctl Callback</H4>
260 The <TT>ioctl</TT> callback is called when the sequencer receives device-specific
261 ioctls. The following two ioctls should be processed by this callback:
264 <TT>IOCTL_SEQ_RESET_SAMPLES</TT></LI>
266 <BR>reset all samples on memory -- return 0
268 <TT>IOCTL_SYNTH_MEMAVL</TT></LI>
270 <BR>return the available memory size
272 <TT>FM_4OP_ENABLE</TT></LI>
274 <BR>can be ignored usually</UL>
275 The other ioctls are processed inside the sequencer without passing to
278 7.2.3 Load_Patch Callback</H4>
279 The <TT>load_patch</TT> callback is used for sample-downloading. This callback
280 must read the data on user-space and transfer to each device. Return 0
281 if succeeded, and -errno if failed. The format argument is the patch key
282 in patch_info record. The buf is user-space pointer where patch_info record
283 is stored. The offs can be ignored. The count is total data size of this
286 7.2.4 Close Callback</H4>
287 The <TT>close</TT> callback is called when this device is closed by the
288 applicaion. If any private data was allocated in open callback, it must
289 be released in the close callback. The deletion of ALSA port should be
290 done here, too. This callback must not be NULL.
292 7.2.5 Reset Callback</H4>
293 The <TT>reset</TT> callback is called when sequencer device is reset or
294 closed by applications. The callback should turn off the sounds on the
295 relevant port immediately, and initialize the status of the port. If this
296 callback is undefined, OSS seq sends a <TT>HEARTBEAT</TT> event to the
300 Most of the events are processed by sequencer and translated to the adequate
301 ALSA sequencer events, so that each synth device can receive by input_event
302 callback of ALSA sequencer port. The following ALSA events should be implemented
305 <TABLE BORDER WIDTH="75%" NOSAVE >
307 <TD NOSAVE><B>ALSA event</B></TD>
309 <TD><B>Original OSS events</B></TD>
323 <BR>MIDI_NOTEOFF</TD>
327 <TD NOSAVE>KEYPRESS</TD>
329 <TD>MIDI_KEY_PRESSURE</TD>
335 <TD NOSAVE>SEQ_AFTERTOUCH
336 <BR>MIDI_CHN_PRESSURE</TD>
340 <TD NOSAVE>PGMCHANGE</TD>
342 <TD NOSAVE>SEQ_PGMCHANGE
343 <BR>MIDI_PGM_CHANGE</TD>
349 <TD>SEQ_CONTROLLER(CTRL_PITCH_BENDER)
350 <BR>MIDI_PITCH_BEND</TD>
357 <BR>SEQ_BALANCE (with CTL_PAN)</TD>
363 <TD>SEQ_CONTROLLER</TD>
369 <TD>SEQ_CONTROLLER(CTRL_PITCH_BENDER_RANGE)</TD>
379 <P>The most of these behavior can be realized by MIDI emulation driver
380 included in the Emu8000 lowlevel driver. In the future release, this module
382 <P>Some OSS events (<TT>SEQ_PRIVATE</TT> and <TT>SEQ_VOLUME</TT> events) are passed as event
383 type SND_SEQ_OSS_PRIVATE. The OSS sequencer passes these event 8 byte
384 packets without any modification. The lowlevel driver should process these
385 events appropriately.
387 8. Interface to MIDI Device</H2>
388 Since the OSS emulation probes the creation and deletion of ALSA MIDI sequencer
389 ports automatically by receiving announcement from ALSA sequencer, the
390 MIDI devices don't need to be registered explicitly like synth devices.
391 However, the MIDI port_info registered to ALSA sequencer must include a group
392 name <TT>SND_SEQ_GROUP_DEVICE</TT> and a capability-bit <TT>CAP_READ</TT> or
393 <TT>CAP_WRITE</TT>. Also, subscription capabilities, <TT>CAP_SUBS_READ</TT> or <TT>CAP_SUBS_WRITE</TT>,
394 must be defined, too. If these conditions are not satisfied, the port is not
395 registered as OSS sequencer MIDI device.
396 <P>The events via MIDI devices are parsed in OSS sequencer and converted
397 to the corresponding ALSA sequencer events. The input from MIDI sequencer
398 is also converted to MIDI byte events by OSS sequencer. This works just
399 a reverse way of seq_midi module.
401 9. Known Problems / TODO's</H2>
405 Patch loading via ALSA instrument layer is not implemented yet.</LI>
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