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This is an old revision of the document!
The protocol used to communicate with the Crazyflie is called the Crazy RealTime Protocol, or CRTP in short. It's a simple protocol mainly designed to suit the radio chip used on the Crazyflie but the protocol can also be used on other physical links.
This page and it's sub-pages describe the protocol itself, not the implementation of some of the more complex functions such as logging and parameters.
Each packet has a 1 byte header and can carry up to 29 bytes data payload. The header field has the following layout:
7 6 5 4 3 2 1 0 +----+----+----+----+----+----+----+----+ | Port | Link | Chan. | +----+----+----+----+----+----+----+----+
Where:
CRTP is implemented in 3 layers:
+-----------------------+ | Application/ports | +-----------------------+ | CRTP packets handling | +-----------------------+ | CRTP Link | +-----------------------+
Current port allocation:
Port | Target | Used for |
---|---|---|
0 | Console | Read console text that is printed to the console on the Crazyflie using consoleprintf |
2 | Parameters | Get/set parameters from the Crazyflie. Parameters are defined using a macro in the Crazyflie source-code |
3 | Commander | Sending control set-points for the roll/pitch/yaw/thrust regulators |
5 | Log | Set up log blocks with variables that will be sent back to the Crazyflie at a specified period. Log variables are defined using a macro in the Crazyflie source-code |
14 | Client-side debugging | Debugging the UI and exists only in the Crazyflie Python API and not in the Crazyflie itself. |
15 | Link layer | Used to control and query the communication link |
Below are details on how CRTP is implemented for different physical links. Currently only the radio link is working but there's some legacy support for the UART still in the code.
The wireless interface will add additional header data like CRC when sending the packet and therefore the packet sent to the wireless interface is only a CRTP packet.
This is currently not implemented but it will potentially replace the serial port link. The use of this is to get CRTP at higher speeds than the radio can transmit.
7 6 5 4 3 2 1 0 +---+---+---+---+---+---+---+---+ | 0xAA | +---+---+---+---+---+---+---+---+ | 0xAA | +---+---+---+---+---+---+---+---+ | Port | Res | Chan. | +---+---+---+---+---+---+---+---+ | Packet length | +---+---+---+---+---+---+---+---+ | DATA 0 | +---+---+---+---+---+---+---+---+ : : : : : : : : : +---+---+---+---+---+---+---+---+ | DATA 30 | +---+---+---+---+---+---+---+---+ | Cksum | +---+---+---+---+---+---+---+---+ +--------+--------+--------+--------+--------+--....--+--------+ | 0xAA | 0xAA | Header | Length | Data0 | Packet | Cksum | +--------+--------+--------+--------+--------+--....--+--------+
Field | Byte | Bit | Description |
---|---|---|---|
Start | 0-1 | 0-2 | Start token for synchronization (0xAAAA) |
Header | 2 | 0-1 | The destination channel |
2 | 2-3 | Reserved for the link layer | |
2 | 4-7 | The destination port | |
Size | 3 | Number of data byte | |
Data | 4-.. | The data in the packet | |
Cksum | 4+size | Checksum. Sum of all the bytes, excluding Start, modulo 256. |