Logging

For more information on how to use this and how this is implemented have a look here.

State machines

Downloading the Table Of Contents

Communication protocol

The log port is separated in 3 channels:

Port	Channel	Function
5	0	Table of content access: Used for reading out the TOC
5	1	Log control: Used for adding/removing/starting/pausing log blocks
5	2	Log data: Used to send log data from the Crazyflie to the client

Table of content access

This channel is used to download the Table Of Contents that contains all the variables that are available for logging and what types they are.

The first byte of each messages correspond a command. All communication on this port are initated by the client and all answer from the copter will contain the same command byte.

TOC command byte	Command	Operation
0	GET_ITEM	Get an item from the TOC
1	GET_INFO	Get information about the TOC and the LOG subsystem implementation

Get TOC item

The GET_ITEM TOC command permits to retrieved the log variables name, group and types from the copter. This command is intended to be requested from all the ID from 0 to LOG_LEN (see GET_INFO).

Request (PC to Copter):
        +--------------+----+
        | GET_ITEM (0) | ID |
        +--------------+----+
Length         1         1

Answer (Copter to PC):
        +--------------+----+
        | GET_ITEM (0) | ID |                                        If index out of range
        +--------------+----+------+------------+--------------+
        | GET_ITEM (0) | ID | Type |   Group    |     Name     |     If returning Item
        +--------------+----+------+------------+--------------+
Length        1          1     1    < Null terminated strings >

Byte	Request fields	Content
0	GET_ITEM	At 0 for GET_ITEM operation
1	ID	ID of the item to be retrieved. The variables are numbered from 0 to LOG_LEN (see GET_INFO command)

Byte	Answer fields	Content
0	GET_ITEM	0 for GET_ITEM operation
1	ID	ID of the item returned
2	Type	Variable type of the element. See variable types list
3..	Group	Null-terminated string containing variable group
..	Name	Null-terminated string containing the variable name

Type, group and name are not sent if the required ID is higher than TOC_LEN-1.

Get Info

The get info command is intended to be requested first when connecting to the copter. This permits to know the number of variable, the limitations of the log implementation and the fingerprint of the log variables.

Request (PC to Copter):
        +--------------+
        | GET_INFO (1) |
        +--------------+
Length         1

Answer (Copter to PC):
        +--------------+---------+---------+-----------------+-------------+
        | GET_INFO (1) | LOG_LEN | LOG_CRC |  LOG_MAX_PACKET | LOG_MAX_OPS |
        +--------------+---------+---------+-----------------+-------------+
Length        1             1         4             1               1

Byte	Request fields	Content
0	GET_INFO	At 1 for GET_INFO operation

Byte	Answer fields	Content
0	GET_INFO	1 for GET_INFO operation
1	LOG_LEN	Number of log items contained in the log table of content
2	LOG_CRC	CRC values of the log TOC memory content. This is a fingerprint of the copter build that can be used to cache the TOC
6	LOG_MAX_PACKET	Maximum number of log packets that can be programmed in the copter
7	LOG_MAX_OPS	Maximum number of operation programmable in the copter. An operation is one log variable retrieval programming

Log control

The log control channel permits to setup, activate, deactivate and remove log packets. Like the TOC access channel the first data byte represents a command.

Control command byte	Command	Operation
0	CREATE_BLOCK	Create a new log block
1	APPEND_BLOCK	Append variables to an existing block
2	DELETE_BLOCK	Delete log block
3	START_BLOCK	Enable log block transmission
4	STOP_BLOCK	Disable log block transmission
5	RESET	Delete all log blocks

Create block

Append variable to block

Delete block

Start block

Stop block

Log data

The log data channel is used by the copter to send the log blocks at the programmed rate. The packet format is

Answer (Copter to PC):
        +----------+------------+---------//----------+
        | BLOCK_ID | TIME_STAMP | LOG VARIABLE VALUES |
        +----------+------------+---------//----------+
Length        1          3           0 to 28

Byte	Answer fields	Content
0	BLOCK_ID	ID of the block
1	ID	Timestamp in ms from the copter startup as a little-endian 3 bytes integer
4..	Log variable values	Packed log values in little endian format

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