Characterization tools

Bench runs

bench.py runs the measurement procedure on an instrument: the charge, the rest and the pulsed discharge down to the cutoff. The procedure and its defaults are the same on every instrument. A backend in tools/fuel_gauge/instruments/ runs it on its hardware: it charges with a CC/CV profile until the charger terminates, runs a discharge profile down to its cutoff, and logs both. Supporting an instrument means adding a backend module and listing it in bench.INSTRUMENTS.

python tools/fuel_gauge/bench.py INSTRUMENT [instrument options] mycell_25c.csv \
    --capacity-mah 70 --vterm 4.45 --ichg 70

It writes the discharge log, the charge log next to it as mycell_25c_charge.csv, and the settings as mycell_25c.json. --help lists the profile’s options; --skip-charge starts from a cell that is already full.

nPM1300-EK

The npm1300-ek backend drives the EK’s shell over the interface MCU’s USB port. The PMIC’s USB port powers the charger: connect it to charge and disconnect it to discharge, when the backend asks. The voltage is measured on the EK rather than at the cell terminals, so measure the resistance in between, see Instrument. The EK can’t end a rest on a voltage slope, so the rests have a fixed length.

python tools/fuel_gauge/bench.py npm1300-ek /dev/cu.usbmodemXXXX mycell_25c.csv \
    --capacity-mah 70 --vterm 4.45 --ichg 70 --ntc 10k

--ntc gives the thermistor type; without one, --temp gives the ambient temperature to log.

Fit and replay

fuel_gauge.py works on the logs:

• fit fits the model to bench logs, and prints the board’s battery node properties and Kconfig defaults.

• replay runs the firmware estimator over a log, with a model file or the model of a board’s firmware.

• synth simulates the bench procedure on a model.

• extract turns the battery service’s verbose logs from a device into a log.

Log format

Every instrument writes the same CSV log, which is what the fit and the replay read (tools/fuel_gauge/fuel_gauge_log.py):

Each row’s current is taken as held over the interval since the previous row, like on the device.