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README.md

midi2cpp | Bridge MIDI 2.0

Waveshare ESP32-P4-WIFI6-DEV-KIT

Dual-stack USB MIDI 2.0 bridge on the Waveshare ESP32-P4-WIFI6-DEV-KIT. Runs TinyUSB host on the USB-A jacks (UTMI PHY, OTG_HS controller at 480 Mbps, rhport 1) and TinyUSB device on the USB-Device USB-C jack (INT PHY, OTG_FS controller, rhport 0) in the same firmware, forwarding MIDI 2.0 channel-voice traffic from any upstream device into the host PC's view of ESP32P4Bridge. Mixed-protocol bus: MIDI 1.0 controllers (Arturia, M-Audio, generic synths) coexist with MIDI 2.0 devices on the same USB-A hub, each routed through its own class driver. ESP-IDF v5.4 build, no Arduino IDE.

esp32-p4-devkit-bridge-midi2 banner

Built against the TinyUSB experiment/midi-coexistence branch on top of upstream master. Running CFG_TUH_MIDI=CFG_TUH_MIDI2=1 requires a tie-breaker between the legacy and MIDI 2.0 host class drivers (both match the same Audio + MIDIStreaming class triple); the branch adds an alt-walk bcdMSC defer (~85 lines, gated by #if CFG_TUH_MIDI2 and #if !CFG_TUH_MIDI2_LEGACY_FALLBACK) plus an opt-in user responder (CFG_TUD_MIDI2_USER_RESPONDER) for per-FB group windows and dynamic FB Names. Staged as follow-up PRs upstream.

Topology

                                  ┌───────────────────────────────────────┐
PC / DAW ─── USB-Device USB-C ───►│ Waveshare ESP32-P4-WIFI6-DEV-KIT      │
              (INT PHY, OTG_FS,   │   rhport 0  m2device + m2ci (responder)│
               LP_SYS swap)       │      ▲                                │
                                  │      │ typed-callback forwarding      │
                                  │      ▼                                │
                                  │   rhport 1  m2host (auto-discovery)   │
                                  └───────────────────────────────────────┘
                                          ▲
                                          │ USB-A (UTMI PHY, OTG_HS)
                                          │ via onboard CH334F hub
                                          │
                                  MIDI 2.0 + MIDI 1.0 devices
                                  up to 4 simultaneous via the hub

MIDI 1.0 + MIDI 2.0 host coexistence

The legacy midi_host.c and the new midi2_host.c (merged upstream via PR #3571) both match the same Audio + MIDIStreaming class triple, so without a tie-breaker the order of usbh_class_drivers[] decides who claims each upstream interface (legacy wins, dropping MIDI 2.0 traffic to byte-stream). The experiment/midi-coexistence branch on top of upstream master adds an alt-walk bcdMSC defer so each driver only claims interfaces that match its own protocol version. With the fix in place, plugging an Arturia MiniLab 25 (MIDI 1.0) and an ESP32-S3 device (MIDI 2.0) into the same hub gives one mount per device, each routed through its own class driver. The bridge forwards tuh_midi2_* typed callbacks through m2device to the PC and instruments the legacy callbacks with diagnostic prints (no MIDI 1.0 forwarding yet). Staged as a follow-up PR upstream.

USB identity

What the PC sees on the device side (USB-Device USB-C jack):

Field Value
VID:PID cafe:4092 (development-only)
Product ESP32P4Bridge
Manufacturer github.com/sauloverissimo

The bridge also runs an m2host instance for the upstream side, with its own MUID seeded from esp_random() masked to 28 bits, so the bridge is a CI Initiator towards upstream devices and a CI Responder towards the PC at the same time.

Build

Requires ESP-IDF v5.4+ with . $IDF_PATH/export.sh sourced and the RISC-V toolchain installed ($IDF_PATH/install.sh esp32p4 once on a fresh IDF).

cd idf
./scripts/fetch_tinyusb.sh         # one-off, ~36 MB clone of the experiment branch
. $IDF_PATH/export.sh
idf.py set-target esp32p4
idf.py build
idf.py -p /dev/ttyACM0 flash monitor    # ToUART jack

The CH343 USB-Serial-JTAG bridge (VID 1a86:55d3) on the ToUART USB-C jack binds to cdc_acm (/dev/ttyACM0). Real DTR / RTS, so idf.py flash auto-resets without a button press.

To override TinyUSB with a local working copy: ln -sfn /path/to/your/tinyusb idf/external/tinyusb && idf.py reconfigure.

Hardware

esp32-p4-devkit-bridge-midi2 banner

Connector / Pin Use
USB-C USB-Device INT device PHY (OTG_FS), routed to the PC. Mandatory LP_SYS.usb_ctrl PHY swap applied at boot to route OTG_FS to PHY0 (GPIO24 / GPIO25)
USB-A jacks (×2) UTMI host PHY (OTG_HS, 480 Mbps), routed through onboard CH334F USB hub. Plug upstream MIDI 1.0 / 2.0 devices here
USB-C ToUART CH343 USB-Serial-JTAG bridge, console stdio @ 115200 8N1, flashing
BOOT button Hold during reset to enter download mode (rarely needed; CH343 auto-reset handles it)
RESET button Reboot

Validation

Plug the USB-Device USB-C into the host PC. Plug any USB MIDI 2.0 device into either USB-A jack. The PC should enumerate cafe:4092 ESP32P4Bridge and expose a MIDI 2.0 endpoint.

  • Linux: lsusb | grep cafe:4092 shows ESP32P4Bridge. amidi -l lists the bridge's MIDI 2.0 group. aseqdump -p <bridge-port> shows the upstream device's NoteOn / NoteOff / CC / PitchBend in real time.
  • Windows: Microsoft MIDI Services Console shows ESP32P4Bridge with Native data format = UMP, MIDI 2.0 Protocol = True.
  • macOS: Audio MIDI Setup shows ESP32P4Bridge.

The UART console mirrors the events:

[boot] esp32-p4-devkit-bridge-midi2
Host UTMI PHY ready (rhport 1)
Device INT PHY ready, full speed (rhport 0)
Both TinyUSB tasks started (device on core 0, host on core 1)
[bridge] PC sees ESP32P4Bridge (cafe:4092)

[host] device idx=0 connected, alt=1 (UMP)
[ep] idx=0 UMP v1.1, 1 FB, MIDI2=1
[ep] idx=0 Endpoint Name: <upstream-device-name>
[fwd idx0] NoteOn ch=0 note=64 vel=0x8000
[fwd idx0] CC ch=0 #74 val=0x12345678

The CH334F hub allows up to 4 MIDI 2.0 devices simultaneously (one direct + a 3-port external hub).

Spec coverage

Tier A bridge.

UMP MT Direction Spec Notes
0x4 MIDI 2.0 Channel Voice upstream→PC M2-104-UM §7 NoteOn / Off (16-bit velocity), CC (32-bit), Pitch Bend (32-bit), Channel Pressure, Poly Pressure, Per-Note Pitch Bend, Program with Bank, all forwarded
0xF UMP Stream both M2-104-UM §11 Endpoint Discovery answered locally on each side, not proxied

UMP Stream Discovery and MIDI-CI traffic are answered locally on each side, not forwarded across the bridge.

Showcase

esp32-p4-devkit-bridge-midi2 banner

Console output during operation:

Event Console line
Boot [boot] esp32-p4-devkit-bridge-midi2
PHY init Host UTMI PHY ready (rhport 1) / Device INT PHY ready, full speed (rhport 0)
Device-side ready [bridge] PC sees ESP32P4Bridge (cafe:4092)
Mount upstream [host] device idx=N connected, alt=A (UMP|byte-stream)
Endpoint Info [ep] idx=N UMP vM.m, F FB, MIDI2=1
Endpoint Name [ep] idx=N Endpoint Name: <product>
NoteOn forwarded [fwd idxN] NoteOn ch=C note=N vel=0xVVVV
NoteOff forwarded [fwd idxN] NoteOff ch=C note=N vel=0xVVVV
CC forwarded [fwd idxN] CC ch=C #I val=0xVVVVVVVV
Pitch Bend forwarded [fwd idxN] PitchBend ch=C val=0xVVVVVVVV
Disconnect [host] device idx=N disconnected

Channel Pressure, Poly Pressure, Per-Note Pitch Bend, and Program Change with bank are also forwarded but do not log to console (re-enable in idf/main/main.cpp if needed).

License

MIT, inherits parent midi2cpp LICENSE.