I've got two pieces of M5StickC a few days ago. After trying out some of the example codes, the display stopped working in one of them (similar to the "M5StickC screen don't work" topic). I uploaded a small test program into it, which writes to serial port, to see if the other parts were still operating. Incidentally this program dumps data from the AXP chip and the results were surprising:
Output from the one without working display:
Output from the correctly working one:
Both outputs were generated while the stick was running on its internal battery.
The source is on github: https://github.com/mdevel1/M5StickC_Battery_Monitor
After finding and removing two loose magnets inside the case (see "Loose magnets inside can short the battery and other components" topic), and power cycling the stick, the AXP chip somehow returned into a working state, the dumped values are back to normal (except which didn't make sense before), and the display is working too.