MIDI & clock

toern_midi.ino owns MIDI parsing, clock generation/following, and note/transport bridging into the sequencer/synths.

Hardware / library setup

• TRS MIDI via Serial (custom MidiSettings, enlarged Serial8 buffers in toern.ino)
• MIDI.h handlers for note on/off, clock, start/stop
• Analog pulse I/O: CLK-OUT pin 37 (pulseClock*), CLK-IN pin 38, SIDEC pin 28 (sidechainOnVoice, MIDI → TRIG). The CLK-IN GPIO interrupt is attached only in BPM orange EXT.

Clock paths

Direction	Entry points
Soft MIDI clock out	updateMidiClockOutput, midiClockTick
External clock in	myClock (MIDI F8) and analogClockIsr (J26, orange EXT only)
Sequencer beat	playTimer / playback aligned with transport state

checkMidi() is called early in loop() for lower latency.

Notes ↔ engine

• Incoming notes → handleNoteOn / handleNoteOff → sample or synth triggers (respecting mutes / child lock)
• Outgoing notes → MidiSendNoteOn and related send helpers when MIDI out is enabled

Editing safely

Clock math and ISR interplay are easy to break. Prefer small, well-tested changes; there are local planning notes (_internal-docs/MIDI_CLOCK_RELIABILITY_PLAN.md) describing past reliability work if you have that folder checked out.

USB and input budget

The USB build exposes MIDI, Audio and Serial interfaces, but musical note/clock/transport parsing and sending use Serial8/TRS. No musical usbMIDI read/send path is implemented. USB audio output is separately connected to the two output mixers; see Audio graph.

checkMidi() stops reading after four non-callback messages per loop. Clock and Note On run through callbacks and do not consume that count. Unread messages remain queued for the next call instead of being discarded. This bounds ordinary message work; it does not guarantee that the hardware UART buffer cannot overflow under excessive input.

MIDI → TRIG selects the voice that pulses J27. It is a digital trigger output, not onboard sidechain compression. MIDI → FOLD folds incoming pitch into the visible grid; OVWR chooses whether incoming MIDI may overwrite occupied cells; voice-select SEL follows the selected voice.