On 1/30/24 03:46, Sahaj Sarup wrote:
Hi, I had a quick question about the ina219 driver https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/hwmon/ti,ina2xx.yaml Is the devictree expecting the shunt-resistor value that is actually on the PCB or is it some calculation based on the calibration value being a static 4096? I am confused because of this comment in the driver
The comment refers to the relationship between calibration value and shunt divider. It (tries to) explain how the values in ina2xx_set_shunt() are calculated. The shunt resistor value provided in devicetree or with platform data should be accurate.
``` In order to keep calibration register value fixed, the product of current_lsb and shunt_resistor should also be fixed and equal to shunt_voltage_lsb = 1 / shunt_div multiplied by 10^9 in order to keep the scale. ``` I am seeing a bit of deviation with a 13 mOhm shunt at 12v 3A, I am getting a reading of 3.14 A from the ina219.
Given that there are always system deviations/inaccuracies, that doesn't sound too bad to me. If you can calibrate against actual measurements, you could try to improve accuracy by providing a slightly different shunt resistor value. Guenter
