ESP32 Forum

Here is what I found from trial & error:

- RTC bits 0-9 require the following initialization to be used as inputs from the ULP:
rtc_gpio_init (IO#) - I don't see why this is required because the function description says "This function must be called when initializing a pad for an analog function." We are obviously not using the pin for a digital function, not analog.
rtc_gpio_set_direction (IO#, RTC_GPIO_MODE_INPUT_ONLY) - This makes more sense, but you would think it would already default to input like the other pins.
- RTC bits 10-15 do not require any initialization to be used as inputs from the ULP.
- GPIO0 still has a 2.2K pullup resistor that I don't know how to disable.

So even though I figured out how to read all the pins, the logic to configure them doesn't make sense.

Once of the examples I looked at earlier on was:

https://github.com/espressif/esp-idf/bl ... ple_main.c

Which Contains this comment:

/* Initialize GPIO0 as RTC IO, input, disable pullup and pulldown */

This comment is false, since the pullup resistor cannot be disabled? (and is not disabled when this program is run)

Are you sure the board you use doesn't have an external pull-up on GPIO0? 2.2K sounds too low to be an internal pull-up, these are usually tens of KOhms.

It is the rev 1 version of the DevkitC.

Huh, no pull-up there. Can I ask how you measured the 2.2K?

I used a 3.3K resistor to pull it down and measured the voltage. The 2.2K was only a rough visual estimate, I did not make a precise measurement or calculation.

There was some problem with devkitc V1 and the auto reset circuit which could be related?