The aim of the logging and parameter framework is to easily be able to log data from the Crazyflie and to set variables during runtime.
Table of content (TOC)
The variables that are available for the logging/parameter framework is decided on compile-time for the Crazyflie firmware. Using C macros variables can be made available to the framework below are two examples, one for parameters and one for logging.
This will make the variables used to control the LED-ring expansion available as parameters. Note that they have different types and that neffect is read-only.
PARAM_GROUP_START(ring) PARAM_ADD(PARAM_UINT8, effect, &effect) PARAM_ADD(PARAM_UINT32 | PARAM_RONLY, neffect, &neffect) PARAM_ADD(PARAM_UINT8, solidRed, &solidRed) PARAM_ADD(PARAM_UINT8, solidGreen, &solidGreen) PARAM_ADD(PARAM_UINT8, solidBlue, &solidBlue) PARAM_ADD(PARAM_UINT8, headlightEnable, &headlightEnable) PARAM_ADD(PARAM_FLOAT, glowstep, &glowstep) PARAM_ADD(PARAM_FLOAT, emptyCharge, &emptyCharge) PARAM_ADD(PARAM_FLOAT, fullCharge, &fullCharge) PARAM_GROUP_STOP(ring)
This will make the variables for roll/pitch/yaw/thrust available for the logging framework. These are the variables used to fill in the data in the Python cfclient FlightTab.
LOG_GROUP_START(stabilizer) LOG_ADD(LOG_FLOAT, roll, &eulerRollActual) LOG_ADD(LOG_FLOAT, pitch, &eulerPitchActual) LOG_ADD(LOG_FLOAT, yaw, &eulerYawActual) LOG_ADD(LOG_UINT16, thrust, &actuatorThrust) LOG_GROUP_STOP(stabilizer)
During the compilation a table of content (TOC) is created that holds all the available variables together with the type and access restrictions. There's one TOC for each framework, one for logging and one for parameters. When the client connects it will download the TOC to know which variables can be used. It's then easy to use the Python API (or another API for accessing them.
All the variables have a name and belong to a group. So in the examples above there's two groups defined: ring and stabilizer. To refer to a variable use the naming convention group.name. If you would like to log the roll variable in the stabilizer group it's access by stabilizer.roll. And if you would like to set the effect variable in the ring group it's accessed using ring.effect.
Using the parameter framework it's possible to both read and write variables in run-time, but note the following:
- There's no thread protection on reading/writing. Since the architecture is 32bit and the largest parameter you can have is 32bit it's safe to write one variable. But if you write a group of variables that should be used together (like PID parameters) you might end up in trouble.
- Only use the parameter framework to read variables that are set during start-up. If variables change during runtime then use the logging framework.
- The reading or writing of a parameter can be done at any time once you are connected to the Crazyflie.
The logging framework is used to log variables from the Crazyflie at a specific interval. Instead of triggering a reading of the variables at certain intervals, the framework is used to set up a logging configuration to that will push data from the Crazyflie to the host. After the host has connected to a Crazyflie and downloaded the TOC it will be possible to setup one of these configurations. Once the configuration is set up and started the Crazyflie will start pushing data to the host. A configuration can be stopped and re-started again. Since there's a finite amount of memory a configuration can be deleted to make room for new ones.
Note the following for the logging framework:
- Once a Crazyflie is connected you can set up new logging configurations. It's only possible to create/start/stop/remove configurations that's already created.
- The interval for a logging configuration is specified in 10th of milliseconds.
Note that variables can be logged as different types from what they have been declared as in the firmware. I.e if a variable is declared as a uint32_t you can log it as a uint8_t (this is being done for the motors in the UI).