On an invensense IMU with fast sampling we need to lower the slave
sample rate for slave sensors such as the built-in AK8963 compass on a
MPU9250.
The slave rate is set as a multiple of the main rate, so it needs to be
much lower for fast sampling. If we leave it high then it greatly
impacts on IMU sample rate.
Without this change a MPU9250 with fast sampling and a compass enabled
will give a gyro rate of around 7200Hz. With this change it gets 7760Hz
FIFO sensors produce data at a well known rate, but samples come in
bunches, so we can't use the system clock to calculate deltaT.
non-FIFO sensors produce data when we sample them, but that rate is
less regular due to timing jitter.
For FIFO sensors this changes makes us use a learned sample rate,
which allows for different clock speeds on sensor and system board.
For non-FIFO sensors we use the system clock to measure deltaT
the overall effect is a fix for sensors that produce samples at other
than the claimed datasheet rate.
this moves to using a 1p filter on the high rate data, followed by
averaging down to 1kHz then a 2p filter to apply configured cutoff
frequency.
It also fixes the FIFO reset to not cause data corruption. We need to
disable all FIFO channels before doing the reset, and wait for the
FIFO to stop in the sensor.
Finally it moves sampling of the MPU6000 and MPU9250 into the main
thread. That significantly improves scheduling performance as we no
longer get long FIFO SPI transfers happening during other tasks. All
transfers happen at the start of the fast loop. That makes timing much
more predictable.
Thanks to Leonard and Paul for help with this design!
When blocking forever there's no reason to call panic later since it
will never going to be reached. This reduces binary size in a few bytes
since the message isn't required anymore.
this allows enable/disable of fast sampling per IMU, making
experimentation easier.
It also fixes the fast sampling to always average over 8 samples, and
fixes the 9250 to use the correct accumulator when not doing fast
sampling
Two cases of what seems to be FIFO alignment errors have been seen on
a Pixracer-beta board with a ICM-20608. At a cost of 2 extra bytes per
transfer we can catch these by looking for sudden temperature changes
caused by bad data in the temperature registers.
Andrew Tridgell
bugobliterator
Lucas De Marchi
murata
mirkix
Randy Mackay
Pierre Kancir
hiro2233