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 26
| 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 |