MIDI Sync Messages (Clock)

MIDI Clock messages are used to synchronize the tempo between Grid and other devices. This allows sequencers, drum machines, DAWs, and other MIDI equipment to stay perfectly in time with each other.

Receiving MIDI Clock Messages

The examples below show how to enable MIDI Clock message handling and how to receive clock messages in a callback.

Enable Clock Messages from USB

Use this when the MIDI Clock is coming from a USB connection.

-- Enable handling and forwarding of clock messages received from USB
-- Note: Add this only to the USB-connected Grid module
rx_mode(2, 0x01 | 0x02)

Enable Clock Messages from the Grid Connection

Use this when the MIDI Clock is received through the Grid network.

-- Enable handling of clock messages received via Grid connection
-- Note: Add this to all modules on the Grid
rx_mode(2, 0x02)

Receiving Clock Messages

When a MIDI Clock message is received, the callback below is executed.

-- Callback for received clock messages
self.rtmrx_cb = function(self, header, rtm_byte)
  print("RTM RX: "..rtm_byte)
end

Understanding the Callback

The rtm_byte value contains the received MIDI real-time message.

Common MIDI Sync messages:

Message	Decimal Value	Description
Clock	248	Sent 24 times per quarter note to keep devices in sync
Start	250	Starts playback from the beginning
Continue	251	Continues playback from the current position
Stop	252	Stops playback

Example

If a DAW sends MIDI Clock while playing, the callback will continuously receive:

RTM RX: 248
RTM RX: 248
RTM RX: 248
...

When playback starts:

RTM RX: 250

When playback stops:

RTM RX: 252

This allows your script to react to transport controls and tempo synchronization events.