Logging and parameter frameworks

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_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_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.

Parameters

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.

Logging

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).

Logging using a function

It is possible to use a function to acquire log values instead of reading from a memory location. The idea is to support more complex use cases where, for instance computations are required to produce the log value.

The macro

LOG_ADD_BY_FUNCTION(TYPE, NAME, ADDRESS)

is used to add a log to a group. TYPE and NAME works the same way as for variable logging, but ADDRESS should point at a logByFunction_t struct instead of a variable. The struct contains a function pointer to the function to call when acquiring data, as well as a void pointer with user data passed that is passed on in the function call.

Example:

    float myLogValueFunction(uint32_t timestamp, void* data) {
// Return the log value
return 47.11;
}

logByFunction_t myLogger = {.aquireFloat = myLogValueFunction, .data = 0};

LOG_GROUP_START(myGroup)
LOG_GROUP_STOP(myGroup)


Note: The logging function is only called if the log is part of an active log configuration. It will be called (approximately) at the interval that is setup in the log configuration.

Logging rates

A common usecase is to log rates (events / s) and there are a set of macros to simplify this task.

The rate logger uses a struct to store data, it is called statsCntRateCounter_t and is initialize using the STATS_CNT_RATE_INITmacro. The struct contains a counter, time information and the latest calculated rate. The initialization macro takes a parameter that specifies the update interval (in ms) and defines how often the rate (delta count / delta time) is calculated. The update interval should match the expected event rate to give meaningful results.

With the STATS_CNT_RATE_DEFINE macro, the struct can be defined and initialized in one line.

To register an event, that is to increase the counter, use the STATS_CNT_RATE_EVENTmacro.

Register the rate counter in a log group witht the STATS_CNT_RATE_LOG_ADD macro.

Example:

    static const uint32_t one_second = 1000;
static statsCntRateLogger_t myCounter;
static STATS_CNT_RATE_DEFINE(myOtherCounter, one_second);

void myInit() {
STATS_CNT_RATE_INIT(&myCounter, one_second);
}

void theFcnThatIWantTheCallRateFor() {
...
STATS_CNT_RATE_EVENT(&myCounter);
...
STATS_CNT_RATE_EVENT(&myOtherCounter);
}

LOG_GROUP_START(myGroup)
// The logging type is implicitly LOG_FLOAT