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| OSS Sequencer Emulation on ALSA</H1></CENTER> |
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| <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 |
| applicaion. 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> |
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