Logging

This describes the new logger, set to 1.

The logger is able to log any ORB topic with all included fields. Everything
necessary is generated from the .msg file, so that only the topic name needs
to be specified. An optional interval parameter specifies the maximum logging
rate of a certain topic. All existing instances of a topic are logged.

The output log format is .

Usage

By default, logging is automatically started when arming, and stopped when
disarming. A new log file is created for each arming session on the SD card. To
display the current state, use logger status on the console. If you want to
start logging immediately, use logger on. This overrides the arming state, as
if the system was armed. logger off undoes this.

Use

The list of logged topics can be customized with a file on the SD card. Create a
file on the card with a list of topics:

The <interval> is optional, and if specified, defines the minimum interval in
ms between two logged messages of this topic. If not specified, the topic is
logged at full rate.

The topics in this file replace all of the default logged topics.

Scripts

There are several scripts to analyze and convert logging files in the
pyulog repository.

Logging dropouts are undesired and there are a few factors that influence the
amount of dropouts:

• Most SD cards we tested exhibit multiple pauses per minute. This shows
  itself as a several 100 ms delay during a write command. It causes a dropout
  if the write buffer fills up during this time. This effect depends on the SD
  card (see below).
• Formatting an SD card can help to prevent dropouts.
• Increasing the log buffer helps.

SD Cards

More important than the mean write speed is the maximum write time per block (of
4 KB). This defines the minimum buffer size: the larger this maximum, the larger
the log buffer needs to be to avoid dropouts. Logging bandwidth with the default
topics is around 50 KB/s, which all of the SD cards satisfy.

By far the best card we know so far is the SanDisk Extreme U3 32GB. This
card is recommended, because it does not exhibit write time spikes (and thus
virtually no dropouts). Different card sizes might work equally well, but the
performance is usually different.

You can test your own SD card with sd_bench -r 50, and report the results to
https://github.com/PX4/Firmware/issues/4634.

The traditional and still fully supported way to do logging is using an SD card
on the FMU. However there is an alternative, log streaming, which sends the
same logging data via MAVLink. This method can be used for example in cases
where the FMU does not have an SD card slot (e.g. Intel® Aero Ready to Fly Drone) or simply to avoid
having to deal with SD cards. Both methods can be used independently and at the
same time.

The requirement is that the link provides at least ~50KB/s, so for example a
WiFi link. And only one client can request log streaming at the same time. The
connection does not need to be reliable, the protocol is designed to handle
drops.

• mavlink_ulog_streaming.py script in Firmware/Tools.
• QGroundControl:
  

• If log streaming does not start, make sure the is running (see
  above), and inspect the console output while starting.
• If it still does not work, make sure that Mavlink 2 is used. Enforce it by
  setting MAV_PROTO_VER to 2.