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Hoverboard firmware

This document is part of the hoverboard firmware documentation.

Datalogger

This document describes the high-speed datalogger feature that can be used to sample several variables at a high speed for later analysis.

The datalogger can sample 8 variables simultaneously and at it runs at the PWM frequency, which can also be divided by an integer if slower sampling is required. This allows sampling for example rotor angle, currents and modulation vector length at a rate necessary for debugging the system.

Configuration

The datalogger is configured off-line directly in the source code.

The basic features, like number of samples and sampling speed, are in Inc/config.h:

#define DATALOGGER_ENABLE
#define DATALOGGER_MAX          0xFF
#define DATALOGGER_TYPE         uint16_t
#define DATALOGGER_COUNT_TYPE   uint8_t
#define DATALOGGER_DIVIDER      7
#define DATALOGGER_CHANNELS		8
#define DATALOGGER_TRIG_TRIP
#define DATALOGGER_SAMPLES_AFTER    32

If the DATALOGGER_ENABLE is defined, then the datalogger feature will be compiled in.

DATALOGGER_MAX tells the number of samples to take. I have not tried more than 256, it may work or there may be some memory-borders that prevent having an array that large... Also config bus currently hard limits the maximum samples to transfer to 14 bits, i.e. 16 ksamples.

DATALOGGER_TYPE is the variable type (byte size) of the variables to sample and DATALOGGER_COUNT_TYPE is the type to be used for the index counter. The first cannot really be changed as the size is hardcoded in several places like in config bus. The latter must be changed so that the amount of samples fits inside that.

The DATALOGGER_DIVIDER tells how often to sample the variables. Setting 0 here samples every PWM period while 1 samples every other and 7 samples only every 8th PWM period.

DATALOGGER_CHANNELS define how many channels there is. Currently some parts of the code (transfering the data over modbus) are hard coded to support 8 channels only.

DATALOGGER_TRIG_TRIP controls whether some faults (like overcurrent & short circuit) trigger the datalogger or not. If this is defined, then the faults trigger datalogger. Should be used together with DATALOGGER_SAMPLES_AFTER.

Finally, the DATALOGGER_SAMPLES_AFTER controls whether sampling is done also before the trigger and only the defined amount of samples is stored after trigger. If not defined, everything is samples after the trigger. This is useful with the DATALOGGER_TRIG_TRIP to see what happened just before the trip.

Triggering and loading data

Triggering of the datalogger is currently done only from modbus. There is a control word called dlog_ctrl currently in register 45 that is used to control the datalogger. It contains following:

  • 0th bit (LSB) is the trigger bit. Setting this to 1 triggers the datalogger
  • 1st bit indicates whether the datalogger is stopped. 0 means logger is running while 1 means it is stopped
  • 2nd bit is used to reset the datalogger (write offsets etc)
  • bits 3...15 address of the sample to read. Note that the largest address is the first sampled

The data to read from the datalogger is in register dlog_data, which is a 8 byte register spanning addresses 46...50. To read data from the datalogger:

  1. Trigger the datalogger by writing 1 to the least significant bit of dlog_ctrl register
  2. Wait until the second bit (bit 1) is 1
  3. Write address of the sample to read to the dlog_cltr bits 2...15 (i.e. address * 4)
  4. Read 4 (16-bit) registers from dlog_data register to get the 4 variables
  5. Repeat 3...5 until all samples are read

Note that the data is stored in reverse order, i.e. the sample with address 0 is the last sample.

The lowest bit tells whether to transfer the first 4 or last 4 sampled variables. I.e. reading address 0 results in the first 4 channels and address 1 the last 4 channels. For this reason you need to read addresses up to two times the number of samples.

If DATALOGGER_SAMPLES_AFTER is defined, after 1st bit indicates that the datalogger has stopped, the address (bits 3...15) indicate the position after where the datalogger stopped writing in the ring buffer, i.e. it contains the offset of the oldest sample. Note that as the logger writes in reverse order, the address should be then decreased from this offset to read the values in order.

Implementation

The variables are configured in Src/main.c so that the pointers to the variables to be sampled are written to datalogger_var[0] through datalogger_var[7]. These are (void *) pointers, but internally currently sample 16 bits. If the variable is less wide (e.g. byte), other bits of the sample may contain rubbish and must be cleaned after fetching the data.

The sampling itself happens in Src/svm.c, after the modulation. This allows for fast sampling at the PWM frequency, but as the sampling is done after modulation it does not affect the modulator performance and as a side benefit it has access to calculated vector lengths as well as it should have fresh current measurement values also.

Copyright

Copyright (C) 2022 Lauri Peltonen