midi2cpp | Host MIDI 2.0
USB MIDI 2.0 host on the Teensy 4.1 (Cortex-M7 @ 600 MHz, 1 MB SRAM). First Arduino IDE host recipe in midi2cpp. Backend (src/teensy41_host_midi2.{h,cpp}) bridges the USBHost_t36 fork branch feature/midi2-host-base (MIDIDeviceBase::umpMode, readUMP, writeUMP) into midi2::Host. Hardware validated under stress: 144,693 UMPs received over 9 min 43 s with zero loss against the UMP test bench flood (see Stress mode).
USBHost_t36 fork. Built against
sauloverissimo/USBHost_t36branchfeature/midi2-host-base(USB MIDI 2.0 host descriptor walk + Alt 1 SET_INTERFACE + raw UMP I/O, +110 LOC over PaulStoffregen master, not yet submitted upstream). OverlayUSBHost_t36.handmidi.cpponto~/.arduino15/packages/teensy/hardware/avr/<version>/libraries/USBHost_t36/.
A pure USB MIDI 2.0 host: one MIDIDevice_BigBuffer slot on the Teensy 4.1 host port. On mount the host fires UMP Stream Endpoint Discovery + MIDI-CI Discovery Inquiry; inbound UMP is decoded by midi2::Host typed callbacks and printed to Serial, one line per message. The USB device port runs as plain Serial for debug, so the Teensy does not enumerate as a MIDI device here; it is not a hub showcase (single slot) and not a bridge (that becomes teensy41-bridge-midi2).
Host-only recipes consume no USB PID (D-030). The peer's identity is runtime-discovered (Endpoint Name, Product Instance ID, MIDI-CI triple); the host's own MUID is seeded from ARM_DWT_CYCCNT, with {0x7D, 0x00, 0x00} as the CI Initiator educational prefix.
Requires Arduino IDE 2.x with Teensyduino 1.60+, the USBHost_t36 fork overlaid (see note above), and the midi2cpp Arduino library on your sketchbook (the midi2 core is bundled).
arduino-cli compile -b teensy:avr:teensy41:usb=serial .
arduino-cli upload -b teensy:avr:teensy41:usb=serial -p <port> .In the Arduino IDE: Tools > USB Type > Serial before Upload (the device-side MIDI stack is intentionally off here).
| Pin / connector | Function |
|---|---|
| USB Device port (micro-USB) | debug print via Serial Monitor at 115200 |
| USB Host port (5-pin header) | enumerates one USB MIDI 2.0 device |
USB Host cable: 5-pin header (GND, D+, D-, 5V, GND) to USB-A receptacle. PJRC sells one at pjrc.com/store/cable_usb_host_t36.html; any pigtail with the right pinout works, confirm with a continuity test first. Pinout: https://www.pjrc.com/store/teensy41.html.
Full UMP surface in budget for the host role.
| UMP MT | Spec | Role | Notes |
|---|---|---|---|
| 0x0 JR Timestamp | M2-104-UM §3.5.2 | rx + tx | 500 ms heartbeat, inbound via onJRTimestamp |
| 0x1 / 0x2 System + MIDI 1.0 CV | M2-104-UM §4.1 | rx | MIDI 1.0 peer fallback path |
| 0x4 MIDI 2.0 CV | M2-104-UM §4.2 | rx + tx | NoteOn/Off, CC, PitchBend, ChannelPressure, Program, Per-Note PB, Reg Per-Note Controller |
| 0xD Flex Data | M2-104-UM §6 | rx | Set Tempo, Set Time Signature |
| 0xF UMP Stream | M2-104-UM §7 | rx + tx | Endpoint Discovery (Initiator) + all identity notifications |
MIDI-CI: Discovery Inquiry as Initiator, auto-fired on mount. Profile / Property Exchange / Process Inquiry are reachable through midi2::Host but not exercised by the bundled sketch. Multi-device via hub and the bidirectional bridge are out of scope for v1 (each fits a sibling recipe without touching the backend).
Pair with any midi2cpp device recipe on the peer side and watch the Serial Monitor:
teensy41-midi2(Teensy 4.1 as device, the natural sibling)teensy41-control-surface(Teensy 4.1 with pots + switches)rp2040-midi2(RP2040 device)waveshare-rp2350-usb-a-midi2(RP2350 device)
Also validates against any USB MIDI 2.0 device, and MIDI 1.0 controllers through the alt 0 fallback.
Set #define HOST_STRESS 1 at the top of the sketch and re-upload to turn the recipe into a zero-loss stress receiver, the pair of the UMP test bench flood (rp2040-promicro-ump-test-bench built with -DBENCH_AUTOFLOOD=ON). NoteOn/NoteOff stop printing per message (a print mid-burst would stall the RX path and fake a loss); the flood's monotonic sequence is checked for contiguity and a verdict prints once the flood goes idle. Same shape as HOST_STRESS in adafruit-feather-rp2040-host-midi2.
Hardware validated 2026-06-11: 144,693 UMPs over 9 min 43 s, one 16-bit sequence wrap-around intact, zero gaps.
USBHost_t36 handles disconnect / reconnect natively; umpMode() returns false during the gap, the edge detector fires notifyDeviceUnmounted, and the next mount triggers a fresh Discovery cycle. No watchdog reset needed (unlike RP2040 PIO-USB).
MIT, inherits parent midi2cpp LICENSE.