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====== Crazyflie LOG subsystem ======

The purpose of the logging is to be able to log variables that are available in the copter during runtime. The Crazyflie log system is design in such a way that the copter firmware is mostly independent from the client and all information required to get the log system to work are communicated at connection time. The copter contains a table of content of all the variable possible to log. The client retrieve the list at connection time. The client then program in the copter log packets (ie. list of variable to log at the same time) to be sent back at regular interval.

This mechanism is used both for regular log operation (ie. user requested log to inspect and debug flight data) but also to update indication in the GUI application.

Each variable to log is contained in a group group and has a name. The system is designed to make it easy to add a log variable in the Firmware and have it available in the ground station GUI:

{{:projects:crazyflie:firmware:logmagic.png?800|}}

===== Firmware usage =====

A couple of macros are declared in //log.h// to define new log variables. All log variables should be in a log group. Example:

<code style="c">
LOG_GROUP_START(stabilizer)
LOG_ADD(LOG_FLOAT, roll, &eulerRollActual)
LOG_ADD(LOG_FLOAT, pitch, &eulerPitchActual)
LOG_ADD(LOG_FLOAT, yaw, &eulerYawActual)
LOG_GROUP_STOP(stabilizer)
</code>

^ Macro                        ^ Usage                                             ^
| LOG_GROUP_START(grp_name)    | Start a log group named //grp_name//              |
| LOG_GROUP_STOP(grp_name)     | Stop log group declaration for group //grp_name// |
| LOG_ADD(type, name, address) | Add a log variable. //type// is the variable type (see bellow), //name// is the name as it will be sent to the ground and //address// is the memory address of the variable |

^ Type defines ^ Corresponding C99 type ^ Note ^
| LOG_UINT8    | uint8_t                |      |
| LOG_UINT16   | uint16_t               |      |
| LOG_UINT32   | uint32_t               |      |
| LOG_INT8     | int8_t                 |      |
| LOG_INT16    | int16_t                |      |
| LOG_INT32    | int32_t                |      |
| LOG_FLOAT    | float                  | IEEE 754 binary32 (single precision float) |
| LOG_FP16     | //N/A?//               | IEEE 754 binary16, intended for log report only (not in memory) |