[Coco] MM1 programmes

[Bob Devries]

FYI:

Active Sense
Category: System Realtime
Purpose
A device sends out an Active Sense message (at least once) every 300
milliseconds if there has been no other activity on the MIDI buss, to let
other devices know that there is still a good MIDI connection between the
devices.
Status
0xFE
Data
None
Errata
When a device receives an Active Sense message (from some other device), it
should expect to receive additional Active Sense messages at a rate of one
approximately every 300 milliseconds, whenever there is no activity on the
MIDI buss during that time. (Of course, if there are other MIDI messages
happening at least once every 300 mSec, then Active Sense won't ever be
sent. An Active Sense only gets sent if there is a 300 mSec "moment of
silence" on the MIDI buss. You could say that a device that sends out Active
Sense "gets nervous" if it has nothing to do for over 300 mSec, and so sends
an Active Sense just for the sake of reassuring other devices that this
device still exists). If a message is missed (ie, 0xFE nor any other MIDI
message is received for over 300 mSec), then a device assumes that the MIDI
connection is broken, and turns off all of its playing notes (which were
turned on by incoming Note On messages, versus ones played on the local
keyboard by a musician). Of course, if a device never receives an Active
Sense message to begin with, it should not expect them at all. So, it takes
one "nervous" device to start the process by initially sending out an Active
Sense message to the other connected devices during a 300 mSec moment of
silence on the MIDI bus.

This is an optional feature that only a few devices implement (ie, notably
Roland gear). Many devices don't ever initiate this minimal "safety"
feature.

Here's a flowchart for implementing Active Sense. It assumes that the device
has a hardware timer that ticks once every millisecond. A variable named
Timeout is used to count the passing milliseconds. Another variable named
Flag is set when the device receives an Active Sense message from another
device, and therefore expects to receive further Active Sense messages.


Regards, Bob Devries; Ipswich, Queensland, Australia