The SequencerEventHandler abstract class is used to define an interface that other class can implement to receive sequencer events. Note that if the last argument of these functions is NULL, the event is sent i. If neither a callback handler is set nor events are enabled, then the signal is emitted. The sequencer core stuff only takes care of two things: The output pool has also a room size, which is used to wake up the thread when it falls into sleep in blocking write mode. Get identifier of a sequencer handle. An event has several storage types according to its usage.

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Zlsa default, the connection of ports via the third client is always allowed if proper read and write subscription capabilities are set both to the source and destination ports.


The control rate is fixed to regardless of HZ. The data field is a union of event data. It includes the time-stamp mode, data storage type, and scheduling priority. Most of controls are accepted. The former means that the port allows to send events to other ports, whereas the latter capability means that the port allows to receive events from other ports.

A client can have one or more ports seauencer communicate between other clients. The event can be dispatched immediately without queueing, alsz. The close callback is called when this device is closed by the application.


This callback must read the data on user-space swquencer transfer to each device. In the case of tick queue, the tempo is controlled in the manner of MIDI.

From this time, events from keyboard are automatically sent to this program.

It is the responsibility of sender client to fill the port id of source. The flags field consists of bit flags which describe several conditions of the sequebcer 1 byte.

Create an ALSA sequencer port.

The Linux MIDI-HOWTO : HOWTO Use MIDI Sequencers With Softsynths.

Some controls are dependent on the synth driver, as well as even on original OSS. The sender must set this value as the destination client. The received timer events are broadcasted to all subscribed clients. In the API, the skew is defined by two values, the skew base and the skew value. Note that scheduling at the current or earlier time is different from the direct dispatch mode even though the event is delivered immediately.

A typical filter program, which receives an event and sends it immediately after some modification, will appear as following:. There is, however, a parameter to change the speed of this queue, called skew. For such events, ALSA sequencer provides several different data storage types.

Although the direct dispatched event needs less memory, it means also that the event cannot be resent if the destination is unable to receive it momentarily. It is the same identifier specified in the call to open. An client that relies on these relative timestamps is the MIDI input port. It is one of the three methods of delivering input events offered by the library.


alsa-seq: Binding to the ALSA Library API (MIDI sequencer).

Source Contents Index alsa QueuedConnection, then the signal is enqueued using the application’s event loop, and it is safe seequencer call any GUI methods in this case. Alternatively, a queue may be shared among several clients. In the future release, this module will be independent. MIDI input was not checked at all, but hopefully it will work.

We can even connect several filter applications which work individually in order to process the MIDI events. There are two memory issues: This library allows to easily create applications managing ALSA clients.

This is the name that should be passed to open in most cases.

On the other hand, in the case of realtime queue, the time resolution is fixed to nanoseconds.