F-Machine BLE Protocol

Introduction

Several F-Machine products are available in Bluetooth LE-enabled variants. These devices share a common BLE protocol using an 18-byte message with a CRC-8 checksum. Commands map to button presses on the physical device UI.

Covered devices:

Device	BLE Name	Secondary Function
Tremblr BT-R	FM-T	Suction
Gigolo BT-R	FM-G	None
Alpha	FM-A	Thrust Depth

BLE Profile

ble_names:
  - "FM-T"
  - "FM-G"
  - "FM-A"
services:
  - uuid: "0xfff0"
    characteristics:
      - uuid: "0xfff1"
        properties: [read, write]
        role: tx
        description: "Command endpoint"
      - uuid: "0xfff4"
        properties: [notify, read]
        role: rx
        description: "Response/notification endpoint"

Device Configuration

Pairing

No special pairing procedure required.

Command Message Format

CMD 64 00 00 00 00 31 32 33 34 00 00 00 00 00 00 00 CRC

Position	Value	Description
Byte 0	Command byte	See command table below
Byte 1	0x64	Constant
Bytes 2–5	0x00	Constant
Bytes 6–9	0x31 0x32 0x33 0x34	Password placeholder (not implemented)
Bytes 10–16	0x00	Constant
Byte 17	CRC byte	CRC-8 checksum

Notification Response Format

CMD 64 00 BITMASK 00 00 00 00 00 00 00 00 00 00 00 00 00 CRC

Position	Value	Description
Byte 0	Command byte	See command table below
Byte 1	0x64	Constant
Byte 2	0x00	Constant
Byte 3	Bitmask byte	See response bitmask below
Bytes 4–16	0x00	Constant
Byte 17	CRC byte	CRC-8 checksum

Commands

Each command represents a button event. Button-held events are followed by a button-released event when released.

Command	Byte	Description
On/Off hold	0x01	On/Off button held down
On/Off release	0x02	On/Off button released
Speed buttons release	0x03	Speed buttons released
Reserved	0x04	Unknown / Reserved
Speed Up hold	0x05	Speed Up button held down
Speed Down hold	0x06	Speed Down button held down
Secondary Function Up hold	0x07	Secondary Function Up button held down
Secondary Function Down hold	0x08	Secondary Function Down button held down
Secondary Function buttons release	0x09	Secondary Function buttons released

The secondary function (0x07/0x08/0x09) controls different physical mechanisms depending on the device: Suction on the Tremblr BT-R, and Thrust Depth on the Alpha. The Gigolo BT-R has no secondary function and does not use these commands.

CRC-8 Checksum

The checksum is computed over the first 17 bytes of the message:

function calcCRC8 (data) {
    let bitCount = 0
    let crc = 0

    for (let i = 0; i < 17; i++) {
        let byte = data[i]
        for (let b = 0; b < 8; b++) {
            if ((byte & (1 << b)) !== 0 ) {
                bitCount++
            }
        }
    }

    const remainder = bitCount % 3
    if (remainder === 0) {
        crc = 222 - bitCount
    } else if (remainder === 1) {
        crc = Math.floor(bitCount / 2) + 111
    } else {
        crc = Math.floor(bitCount / 3) + 177
    }

    return crc
}

Response bitmask

Although multiple buttons may be held simultaneously, the device only ever reports the highest value bit at any one time.

000xxxxx
   ||||\_ Is On/Off Held (`0x01`)
   |||\__ Is Speed Up Held (`0x02`)
   ||\___ Is Speed Down Held (`0x04`)
   |\____ Is Secondary Function Up Held (`0x08`)
   \_____ Is Secondary Function Down Held (`0x10`)

An example, if Speed Up and Secondary Function Up are both held, only 0x08 will be returned until Secondary Function Release is sent, then it will reply 0x02 as Speed Up is still held. Once nothing is held it will go back to 0x00.

Notes

• All three BLE devices (Tremblr BT-R FM-T, Gigolo BT-R FM-G, Alpha FM-A) share this protocol. The secondary function commands (0x07/0x08/0x09) are only applicable to the Tremblr BT-R (suction) and the Alpha (thrust depth); the Gigolo BT-R has no secondary function.
• Password bytes (0x31 0x32 0x33 0x34) are intended for authentication but not implemented in current firmware. It's unknown whether firmware can be upgraded.
• CRC formula: based on bitCount mod 3, applies one of three linear transformations to the total bit count.

Sources

• GitHub Issue (docs.buttplug.io#13)