ESP32 Forum

Hello everyone!

I have a code, which starts early (before app_main, via __attribute__((constructor))) and reads all GPIOs (its config, connected signals etc) to find out, which GPIOs are **reserved**. So I found that pins 6..11 have **reserved** flag (SPI0 flash chip access) and pins 34..39 are marked as **reserved** as well.

Documentation says nothing about pins 34..39 except that they are input-only pins.

Can anyone explain why pins 34..39 are reserved?

Thank you!

Those pins (34–39) are input-only and don’t have internal pullups or pulldowns, which limits their flexibility. They're often marked as "reserved" or restricted in low-level system access because they’re typically used for specific purposes like sensors or special debug functions. Not truly “reserved” in the SPI0 sense, but likely flagged to prevent accidental output use.