@felmue

The data seems to be random indeed, however, it is always the same.
We did notice shark fin like signals on the i2c lines on 400k. We reduced it to 100k but the results stayed the same. We do not believe that the bad signal quality is causing the current issue we are having. On a good working board the signals look identical.

For reference, here is inmage of the signal quality of the SCL/SDA line on 400k speed on the good board.:

The register values are taken with 100000 speed.
I think i forgot register 0x22. I've tested it and added it here:

We've also tested writing the value 0 to 10 on register 0x04. On the good board we can read back the correct value. But on the bad board it always returns 0x78

We are using the M5 Stack with ESP-IDF. We have a CoreS3, Battery module and a CatM module.

After running in the field for a while. some device are not coming online anymore.

We tried resetting the device on location without success.
The only way to properly reset the functionality is to unmount the battery and remount is (Making sure no power is going to the M5Stack.)

We can also not fix the device be rewriting firmware.

It turns out the power chip (Axp2101) isn't responding properly anymore. When we send command to it, it doesn't seem to work. (Sending 0x01 to 0x10 should power off the device, this doesn't happen).

It's not a I2C problem, we can succesfully contact the RTC and the IMU on the same bus.

We can write new firmware and flash it and the problem still occusrs, i can run some tests to get to the bottom of it.

We've compared registers in the AXP2101 from a good sample and a bad sample.

What could cause this behaviour?

How can it be resolved (using software preferably)