03-04-2021, 01:21 PM
Operating system and application specific. And bootloader config specific at power up. I'm guessing you've seen a green LED at boot up set by u-boot, and a flashing blue led in Mobian, probably from Phosh telling you there's a pending notification. It can only flash while the CPU is active, so when it sleeps you may or may not have a constant blue light. Any application with sufficient privileges can set the LED state.
