BLE HID Central (HOGP - HID over GATT Profile) module for ZMK firmware.

This module allows ZMK keyboards to connect to external BLE HID devices (mice, trackpads) and forward their input through the keyboard.

• HOGP Central: Connect to BLE HID devices as a central
• Auto-reconnect: Automatically reconnect to bonded devices on boot
• Pairing mode: Manual pairing with configurable timeout
• Serial commands: Debug and control via USB serial console

manifest:
  remotes:
    - name: hh
      url-base: https://github.com/hh
  projects:
    - name: zmk-hogp
      remote: hh
      revision: main

Many BLE trackpads use LE Legacy pairing, but upstream ZMK forces Secure Connections Only. Apply the included patch:

./zmk-hogp/scripts/apply-patches.sh

Or manually patch zmk/app/Kconfig:

 menuconfig ZMK_BLE
     select BT
     select BT_SMP
-    select BT_SMP_SC_PAIR_ONLY
+    select BT_SMP_SC_PAIR_ONLY if !ZMK_HOGP

Add to your board's _defconfig or prj.conf:

# Enable HOGP central
CONFIG_ZMK_HOGP=y
CONFIG_ZMK_HOGP_LOG_LEVEL_DBG=y

# Enable serial commands (auto-enabled with HOGP)
CONFIG_ZMK_SERIAL_CMD=y
CONFIG_ZMK_USB_LOGGING=y

# Required: BLE Central role
CONFIG_BT_CENTRAL=y
CONFIG_BT_GATT_CLIENT=y

# Required: Allow Legacy Pairing for trackpads
CONFIG_BT_SMP_SC_PAIR_ONLY=n
CONFIG_BT_SMP_ENFORCE_MITM=n

# Recommended: Bonding settings
CONFIG_BT_KEYS_OVERWRITE_OLDEST=y
CONFIG_BT_MAX_PAIRED=7

Commands must be prefixed with !:

1. Build and flash firmware with USB logging enabled
2. Open serial console: picocom /dev/ttyACM0 -b 115200
3. Put your trackpad in pairing mode
4. Send !pair to start scanning
5. Device will connect when HID Service UUID (0x1812) is found
6. Switch keyboard to BLE output (!ble) to forward trackpad data to host

This means the trackpad uses Legacy pairing but ZMK is forcing Secure Connections Only.

Fix: Apply the ZMK patch (see Installation step 3) and ensure these configs are set:

CONFIG_BT_SMP_SC_PAIR_ONLY=n
CONFIG_BT_SMP_ENFORCE_MITM=n

Ensure USB logging is enabled:

CONFIG_ZMK_USB_LOGGING=y

The trackpad data flows through BLE, not USB. Switch the keyboard to BLE output:

!ble

For custom report handling:

#include <zmk/hogp/hogp.h>

void my_report_handler(const uint8_t *data, uint16_t len) {
    // Process HID report (e.g., forward to host)
}

hogp_register_report_callback(my_report_handler);

┌─────────────────┐     BLE HOGP     ┌──────────────┐
│   BLE Trackpad  │ ───────────────> │   Keyboard   │
│  (HID Peripheral)│                  │ (HID Central)│
└─────────────────┘                  └──────┬───────┘
                                            │
                                            │ BLE/USB HID
                                            v
                                     ┌──────────────┐
                                     │     Host     │
                                     │   Computer   │
                                     └──────────────┘

MIT License - See LICENSE