Draft:MultiWii Serial Protocol

MultiWii Serial Protocol (MSP). is a communication protocol originally developed for the MultiWii flight controller software, designed to facilitate communication between flight controllers and external devices. The protocol allows for a wide range of functionalities including configuration, telemetry, and control commands. Over time, MSP has been adopted by various other flight control systems, such as Betaflight, Cleanflight, and iNav

History

The MSP was first introduced with the MultiWii flight controller, an open-source project that used Arduino-based hardware for controlling multi-rotor aircraft. As the popularity of MultiWii grew, so did the adoption of MSP by other flight controller projects. The protocol's simplicity and efficiency made it an ideal choice for resource-constrained environments typical of early flight controllers.

Protocol Overview

MSP is a binary protocol that uses a specific message structure to ensure reliable communication. Each MSP message consists of the following components:

• Header: The start of each MSP message is denoted by the characters $M< for requests from the ground station to the flight controller and $M> for responses from the flight controller.
• Size: A single byte indicating the length of the payload.
• Command: A single byte indicating the type of command or response.
• Payload: A variable-length field containing the data associated with the command.
• Checksum: A single byte used for error-checking, calculated as the XOR of all bytes in the size, command, and payload fields.

Common MSP Commands

Some of the commonly used MSP commands include:

• MSP_API_VERSION (0x01): Retrieves the API version of the flight controller firmware.
• MSP_FC_VERSION (0x03): Retrieves the flight controller firmware version.
• MSP_BOARD_INFO (0x04): Retrieves information about the flight controller board.
• MSP_STATUS (0x101): Retrieves the current status of the flight controller.
• MSP_RAW_IMU (0x102): Retrieves raw sensor data from the IMU (Inertial Measurement Unit).
• MSP_RC (0x105): Retrieves the current values of the RC (Remote Control) channels.
• MSP_ATTITUDE (0x106): Retrieves the current attitude (roll, pitch, yaw) of the aircraft.
• MSP_ALTITUDE (0x107): Retrieves the current altitude.
• MSP_SET_RAW_RC (0x200): Sets the values of the RC channels.
• MSP_ARM (0x240): Arms the flight controller.
• MSP_DISARM (0x241): Disarms the flight controller.

Applications

MSP is widely used in various applications within the realm of unmanned aerial vehicles (UAVs) and drones. Its primary applications include:

• Configuration Tools: Ground station software such as Betaflight Configurator uses MSP to configure flight controller parameters.
• Telemetry: MSP allows for real-time telemetry data to be sent from the flight controller to external devices, providing critical flight information.
• Control Interfaces: MSP enables the development of custom control interfaces, allowing developers to create applications that interact with the flight controller.

Adoption and Future Development

MSP has been adopted by numerous flight control systems due to its lightweight and efficient design. Its open nature encourages community contributions and adaptations. As drone technology continues to evolve, so too does the MSP, with ongoing development to support new features and capabilities.