The CRTP (Crazy RealTime Protocol) is the name of the protocol used to communication with the Crazyflie. The protocol is used for multiple physical layers:

• UART
• USB
• 2.4 GHz NordicSemi Radio
• …

The CRTP packet consists of 32 bytes of data:

The ports numbers are composed of: Priority, task number and message number. * The priority is set by the 2 MSB of the port number. It permit to each task to chose in a per message basis the priority of its messages * The task number is used by CRTP to distribute the messages to the different tasks in the copter * Finally the message number is composed by the two LSB and permit to have 4 different communication channel per task.

A proposed notation is P:T:N, P is the priority, T is the task number and N the message number. The port number is then built as follow:

+---+---+---+---+---+---+---+---+
| P   P | T   T   T   T | N   N |
+---+---+---+---+---+---+---+---+

#define PORT(P,T,N) ((P<<6) | (T<<2) | N)

NOTE: This is currently being changed!

Below is the structures for the packages both for the wired serial interface and for the wireless interface. The limitation for the length of the data is set so that it will fit inside one packet for the wireless transmission.

Wireless:
+------+------+
| PORT | DATA |
+------+------+
| PORT |  <31 |
+------+------+
    1     x   
The wireless firmware adds ADDRESS, PID, LENGTH and CRC automatically.

TODO

Serial port:
+-------+------+--------+------+-----+
| START | PORT | LENGTH | DATA | CRC |
+-------+------+--------+------+-----+
| 0xAAAA| PORT |   <31  | DATA | CRC |
+-------+------+--------+------+-----+
    2      1       1       x      1     :byte

This port is used as a one-way text console. Printouts using printf will be sent on this port and can be read by a receiver if connected.

+--------+
|  Data  |
+--------+
   1-31      :bytes

The contents of the buffer on the copter side is sent if any of the following is fulfulled:

• The output buffer (of 31bytes) is full
• A “newline” character has to be send (\n and/or \r)
• A flush command as been issued

The purpose of the logging is to be able to log variables that are available in the copter during runtime. The available variables are listed using a TOC that can be read from the copter. A logging block can then be registered consisting of there variables and the data will be sent periodically via CRTP to a receiver.

This port is used to access the loggable variables table of content. The first byte of the message is a message ID, three messages ID are defined:

The upstream ID are commands and are sent alone. The downstream have the following formats:

Bytes     1       1          1    Null terminated strings
        +---+------------+------+----------+--------------+
        | 0 |            |      |          |              |
        +---+   Var ID   | Type |  Group   |     Name     |
        | 1 |            |      |          |              |
        +---+------------+------+---+------+--------------+
        | 3 | Num. Vars  |  CRC32   |
        +---+------------+----------+
Bytes     1       1           4

The logging variables are sequentially requested by the receiver until the end. When the last loggable variable is reached it has the ID 0 'Last TOC element'. The reset command permits to reset the TOC pointers so that the next sent TOC element will be the first one. The Get CRC commands also returns the number of loggable variables.

The CRC32 is a hash of the copter's loggable variable TOC. The aim of having this is to be able to cache data on the receiver end and to quickly check the validity of it when connecting.

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The parameters system aims at making accessible all the gettable and settable parameters of the copter. In the copter a table of parameters is hold and can be retrieved. In this table every parameter name is associated with an ID and a group name. Three ID are used to acces the TOC and the paramareters:

This ports permits to access the parameters table of content. The first byte of the message is a message ID, three messages ID are defined:

The upstream ID are commands and are sent alone. The downstream have the following formats:

Bytes     1       1          1    Null terminated strings
        +---+------------+------+----------+--------------+
        | 0 |            |      |          |              |
        +---+  Param ID  | Type |  Group   |     Name     |
        | 1 |            |      |          |              |
        +---+------------+------+---+------+--------------+
        | 3 | Num. Param |  CRC32   |
        +---+------------+----------+
Bytes     1       1           4

The parameters are sequentially requested by the PC until the end. When the last parameter is reached it has the ID 0 'Last TOC element'. The reset command permits to reset the TOC pointers so that the next sent TOC element will be the first one. The Get CRC commands also returns the number of parameters.

The CRC32 is a hash of the copter TOC. This is aim at implementing caching of the TOC in the PC Utils to avoid fetching the full TOC each time the copter is connected.

TODO

TODO

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