alsa-seq-0.6: Binding to the ALSA Library API (MIDI sequencer).

Stabilityprovisional
MaintainerHenning Thielemann
Safe HaskellNone

Sound.ALSA.Sequencer.Event

Contents

Description

This module contains functions for working with events. Reference: http://www.alsa-project.org/alsa-doc/alsa-lib/group___seq_event.html

Synopsis

Output

If you send an event but you do not hear something, then check the following conditions:

  • Check whether your event was actually delivered. E.g. use the event monitor aseqdump in order to see sent messages.
  • If the message was not delivered, maybe you quit the program too early and thus destroyed pending messages. Use syncOutputQueue at the end of the program in order to wait for all messages to be sent.
  • Make sure the sequencer supports output and the target port supports input.
  • Make sure to setup a connection to the receiver.
  • Make sure to have called drainOutput after output.
  • If you use a timestamp in an event, make sure you also declare a queue (and create one before).
  • Make sure you started the queue you used for sending.
  • Be aware of that QueueStart clears the queue before running the queue. That is, events sent before QueueStart are deleted. If you want to keep these events, then use QueueContinue instead.

outputSource

Arguments

:: AllowOutput mode 
=> T mode 
-> T 
-> IO Word

the number of remaining events (or bytes?)

Output an event and drain the buffer, if it became full. Throws exceptions. See also: outputDirect, outputBuffer, outputPending, drainOutput, dropOutput, extractOutput, removeOutput

outputBufferSource

Arguments

:: AllowOutput mode 
=> T mode 
-> T 
-> IO Word

the byte size of remaining events

Output an event without draining the buffer. Throws -EAGAIN if the buffer becomes full. See also output.

outputDirectSource

Arguments

:: AllowOutput mode 
=> T mode 
-> T 
-> IO Word

number of bytes sent to the sequencer

Output an event directly to the sequencer, NOT through the output buffer. If an error occurs, then we throw an exception. See also output.

outputPendingSource

Arguments

:: AllowOutput mode 
=> T mode 
-> IO Word

size of pending events (in bytes)

Return the size (in bytes) of pending events on output buffer. See also output.

extractOutputSource

Arguments

:: AllowOutput mode 
=> T mode 
-> IO T

the first event in the buffer (if one was present)

Extract the first event in output buffer. Throws (Errno 2) exception if output buffer is empty. See also output.

removeOutput :: AllowOutput mode => T mode -> IO ()Source

Remove the first event in output buffer. Throws an exception on error. See also output.

drainOutputSource

Arguments

:: AllowOutput mode 
=> T mode 
-> IO Word

byte size of events remaining in the buffer.

Drain output buffer to sequencer. This function drains all pending events on the output buffer. The function returns immediately after the events are sent to the queues regardless whether the events are processed or not. To get synchronization with the all event processes, use syncOutputQueue after calling this function. Throws an exception on error. See also: output, syncOutputQueue.

dropOutput :: AllowOutput mode => T mode -> IO ()Source

Remove events from both the user-space output buffer, and the kernel-space sequencer queue. See also: drainOutput, dropOutputBuffer, removeOutput.

dropOutputBuffer :: AllowOutput mode => T mode -> IO ()Source

Remove events from the user-space output buffer. See also: dropOutput.

syncOutputQueue :: T mode -> IO ()Source

Wait until all events of the client are processed.

Input

input :: AllowInput mode => T mode -> IO TSource

Get an event from the input buffer. If the input buffer is empty, then it is filled with data from the sequencer queue. If there is no data in the sequencer queue, then the process is either put to sleep (if the sequencer is operating in blocking mode), or we throw EAGAIN (if the sequence is operating in non-blocking mode).

We may also throw ENOSPC, which means that the sequencer queue over-run and some events were lost (this clears the input buffer).

inputPendingSource

Arguments

:: AllowInput mode 
=> T mode 
-> Bool

refill if empty?

-> IO Word

number of events in buffer

Returns the number of events in the input buffer. If the input buffer is empty and the boolean argument is true, then try to fill the input buffer with data from the sequencer queue. See also: input.

dropInput :: AllowInput mode => T mode -> IO ()Source

Remove events from both the user-space input buffer, and the kernel-space sequencer queue. See also: dropInputBuffer, removeOutput.

dropInputBuffer :: AllowInput mode => T mode -> IO ()Source

Remove events from the user-space input buffer. See also: dropInput.

Data types

data T Source

Constructors

Cons 

Fields

highPriority :: !Bool
 
tag :: !Tag
 
queue :: !T
 
time :: !T
 
source :: !T
 
dest :: !T
 
body :: !Data
 

Instances

simple :: T -> Data -> TSource

Construct an ALSA sequencer event from very few information. Most fields are initialized with sensible defaults. You may use this as a start and alter its fields for your special needs.

 (Event.simple myAddr (Event.simpleNote (Event.Channel 0) (Event.Pitch 60) Event.normalVelocity)) {Event.dest = destAddr}

simpleNote :: Channel -> Pitch -> Velocity -> NoteSource

Make a note whose unspecified fields contain 0.

data Ctrl Source

Constructors

Ctrl 

Instances

data Custom Source

Constructors

Custom 

Fields

custom0 :: !Word32
 
custom1 :: !Word32
 
custom2 :: !Word32
 

newtype Tag Source

Constructors

Tag 

Fields

unTag :: Word8
 

Instances

newtype Tempo Source

Constructors

Tempo 

Fields

unTempo :: Int32
 

newtype Value Source

Constructors

Value 

Fields

unValue :: Int32
 

newtype Channel Source

Constructors

Channel 

Fields

unChannel :: Word8
 

newtype Pitch Source

Constructors

Pitch 

Fields

unPitch :: Word8