*solved/confirmed* Oak won't boot with pin 4 held low

[postuma]

on the two Oaks I have left available to test, it seems they won't boot if pin 4 is held to ground by way of a 10K resistor. Can anyone confirm?

[PeterF]

I'll check soon, but the only 'documented' pins I know off hand to be cautions of are "Pins 0, 1, and 2 must not be held low at boot" and "Pin 6 must not be held high at boot". Just a sanity check - do you mean the pin marked P4, or the fourth one down (from VCC) - as that is P2?

Edit: No, I can confirm - P4 (TX) to GND via 10k results in no startup, and ~30ma power consumption instead ~75ma power consumption. I have absolutely no idea why though - as far as I can tell, that pin, GPIO1 isn't one of the 'magic' bootup pins, and i can't see why it wouldn't work, except for also being the default serial TX pin??

[postuma]

Thanks Peter for confirming! I should be clear that the won't-boot-if-pulled-low issue occurs also with weaker and stronger pull-downs. Perhaps the Pinout diagram should be amended to clarify that pins 0, 1, 2 and 4 should not be held low at boot. Pin 3 can be held low without problem.

After a fair bit of digging around the ESP8266 GPIO pin 1 (Oak's pin 4), it would seem that in its role as the serial send pin, U0TXD, it is also a strapping pin for chip_test_mode(1: normal mode; 0: chip_test_mode). As such, it should not be pulled down when the system is powered on. It is repurposed as a general IO pin after boot/initialization.

Issue closed?

[PeterF]

Thanks for that... you found the doc I was looking for - I was sure there was more than three pins that could effect the ESP8266 bootup. I'll amend the wiki page as I found the espressif caution now that I know I wasn't imaging things. You should be able to edit your first post to change the title if you want to mark the thread as "solved"