RtMIDI feature translation¶

Queue messages as bytes¶

RtMIDI translates all ALSA messages to bytes. 1

It is left the same way, although data types might be changed to ensure bytes are always 8-bit (something like uint8_t).

The ALSA sequencer has a maximum buffer size for MIDI sysex events of 256 bytes.

If a device sends sysex messages larger than this, they are segmented into 256 byte chunks.

RtMIDI rejoins 256-byte SysEx message chunks to a single bytearray.

The initial source contains two ways to do that.

First one uses the system time.

(void)gettimeofday(&tv, (struct timezone *)NULL);
time = (tv.tv_sec * 1000000) + tv.tv_usec;

Second one uses the ALSA sequencer event time data and was implemented by Pedro Lopez-Cabanillas. 2

The second one was commented quite a bit and it can be found in a current source code.

Uses an internal function and different ordering, but it doesn’t seem to influence anything and this doc section is about to be removed.

Before:

snd_seq_set_client_name(seq, client_name);
amidi_data->seq = seq;

Now:

amidi_data->seq = seq;
set_client_name(amidi_data, client_name);

Footnotes

1: I’m not sure if it helps to rejoin SysEx messages or it is done as a way to unify output for Alsa, Jack, etc.
2: LibC manual on getting elapsed time.