LED shines when GPIO2 low on ESP-12?

[deshipu]

I just noticed a strange thing. If I set the GPIO2 pin to low (or enable PWM on it), the blue serial LED, which normally blinks when there is serial communication, switches on. I would expect that LED to be connected to GPIO3 or GPIO1, not GPIO2, so I'm not sure what is happening there. Anybody had a similar experience?

[platforma]

Nope, seems okay here. I have ESP12-E. Tried both PWM and Pin.OUT/Pin.IN set to low for pin 2. Does the LED turn off when you set the pin to other values (high or PWM)?

[pfalcon]

Yes, ESP-12 has an on-module blue LED, on GPIO2, active low. I don't see it blinking with serial communication (except for when using BootROM bootloader for programming, but that's bootloader blinking it, not serial communication, i.e. it in no way tied to UART).

[deshipu]

That makes sense, thanks.
At the bootloader time, everything from GPIO1 is echoed on GPIO2 (possibly for debugging), so that would explain why it blinks then.

[pfalcon]

A bit better explanation is that GPIO2 is TXD1, i.e. TX of TX-only UART1, intended to be used for logging. Apparently, bootloader dumps quite a lot there. It would be interesting to see what it writes there, I don't believe I ever saw someone describing that (I bet it's 74880 baud or whatever it is).

This made me think: we forgot to disable OS logging to UART0 in the release %).