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:

• Port: Used to identify the functionality or task that is associated with this message
• Link: Reserved for future use
• Channel: Used to identify the sub-task/functionality

CRTP is implemented in 3 layers:

• CRTP Link is responsible for transferring the packets between the Crazyflie and the host. It will typically handles packet size and error detection.
• CRTP Packet handling delivers the packet to the right subsystem in the Crazyflie and in the host control software.
• Application/ports represents the subsystems that sends and receives messages.

Current port allocation:

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.

The serial port is configured in 115200 8N1. CRTP packets are sent and received asynchronously using the following packet format:

  7   6   5   4   3   2   1   0
+---+---+---+---+---+---+---+---+
|             0xAA              |
+---+---+---+---+---+---+---+---+
|             0xAA              |
+---+---+---+---+---+---+---+---+
|      Port     |  Res  | Chan. |
+---+---+---+---+---+---+---+---+
|         Packet length         |
+---+---+---+---+---+---+---+---+
|            DATA 0             |
+---+---+---+---+---+---+---+---+
:   :   :   :   :   :   :   :   :
+---+---+---+---+---+---+---+---+
|            Cksum              |
+---+---+---+---+---+---+---+---+

+--------+--------+--------+--------+--------+--....--+--------+
|  0xAA  |  0xAA  | Header | Length | Data0  | Packet | Cksum  |
+--------+--------+--------+--------+--------+--....--+--------+

To send setpoints to the commander send:

0xaa 0xaa 0x30 0x0e 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x3e

To ping Crazyflie:

 ->   0xaa 0xaa 0xf0 0x01 0x01 0xf2     # Sent to the copter 
 <-   0xaa 0xaa 0xf0 0x01 0x01 0xf2     # Received from the copter