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Advanced Linux Sound Architecture (ALSA) - Sequencer
====================================================
http://www.inter.nl.net/users/F.K.W.van.de.Pol/alsa/
By Frank van de Pol, F.K.W.van.de.Pol@Inter.nl.net
ALSA Sequencer
==============
This directory contains a prototype for the ALSA Sequencer. Beware that this
is *development* code. My motivation for writing this prototype is to get a
proof of concept and feasibility for this project. The eventually
(hopefully) working prototype can be used for discussing sequencer APIs.
Current status (last updated 31 Aug 1998):
=========================================
* Allows scheduling and routing of both real-time events and events with a
midi tick timestamp. The sequencer uses tempo (us/beat) and specified PPQ
resolution (ticks/beat) to calculate the ticks from time.
* Both user-land and kernel clients can connect, send events, receive events
and communicate directly with the sequencer (ioctl()). Reads and writes
for user-land clients can be batched, blocking io and select() is
supported. Kernel clients can directly enqueue data to the priority queue
and use a call-back for incoming data.
* A simple timer driver for the system clock (100Hz) is provided
(snd-seq-systimer).
* The time and song position for the queues are maintained by a software
timer. It can be started and stopped by sending SND_SEQ_EVENT_START and
SND_SEQ_EVENT_STOP messages to the timer port (client 0, port 0).
* Support for fixed length events and variable length events (used for
system exclusive data)
* proc interface (/proc/asound/sequencer-*) to see what clients have
registered, get memory status info, queue status etc.
* Muliple independent queues can be used to run different time/tempo
independend application. (ie. multi-user sequencing)
* Included sample clients (in the test/seq/ directory):
- readtime : display information on the sequencer timer.
- usertest1 : decoding of received events to text
- usertest2 : a simple user-land driver that plays received events to
the MIDI output port (/dev/sndmidi00). It uses Round-Robin
scheduling to get reasonable performance. Tested with a
Gravis Ultrasound MAX card and external Yamaha XG
synthesizer.
It supports the following events:
- SND_SEQ_EVENT_NOTEON
- SND_SEQ_EVENT_NOTEOFF
- SND_SEQ_EVENT_PGMCHANGE
- SND_SEQ_EVENT_PITCHBEND
- SND_SEQ_EVENT_CONTROLLER
- SND_SEQ_EVENT_START (send real-time start)
- SND_SEQ_EVENT_STOP (send real-time stop)
- SND_SEQ_EVENT_CONTINUE (send real-time continue)
- SND_SEQ_EVENT_SYSEX
- playmidi : a player for standard midi files (SMF). It is based on the
readmidi library, so only type 0 midi files are supported.
Output is send to client 1 (hard coded), so either
usertest1 or usertest2 should be started first.
- kernel-client1
: a test for the kernel API, just bounces events to next
client
- kernel_client_midi
: a kernel API test which implements a MIDI driver (similar
like the usertest2 driver)
- kernel_client_midi2
: registers a MIDI driver using the midisynth mid-level
driver.
Installation:
=============
- Compile the sequencer:
(directory alsa-driver/kernel/seq)
$ make
- make sure ALSA is loaded
- load the sequencer (need root privileges)
$ insmod snd-seq.o
- load the timer (need root privileges)
$ insmod snd-seq-systimer.o
- Compile the clients:
(directory alsa-driver/test/seq)
$ make
- run the clients
start our synth driver:
$ usertest2 (preferably as root)
and in some other session start playback of a MIDI file (make sure your
synth gear is switched on and the faders on your mixing desk are open..)
$ playfile pick_up_the_pieces.mid
- Have fun.
Todo:
=====
Many things....
- kill some bugs
- work out client & port registration/lookup
- add system announcements
- add open on demand for midisynth
- clean events on client termination
- add synchronization
- add more clients
References on the web:
======================
ALSA: http://alsa.jcu.cz/
ALSA Sequencer: http://www.inter.nl.net/users/F.K.W.van.de.Pol/alsa/
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