Unable to use gpio 16 and 17

[mrdebug]

Hi, I have esp32 development board on my desk.
Iìm trying to use gpio 16 and 17 as uarts on digital out but it does not work.
Is my development board broken or it is a normal behaviour?

[ESP_krzychb]

Hi mrdebug,

GPIO16 and 17 may be used for communication with flash or PSRAM, depending on particular chip or module that you have on your development board.

For example see the datasheet of ESP32-WROVER-E module.

ESP32-WROVER-E-flash-psram.png (439.94 KiB) Viewed 3480 times

What is exact ESP32 chip variant or module that you have?

[mkeyno]

I use wroom and both pins are free, however, when I use simple lrdc or
timer library, they work fine, but if use an extra timer they are not
working
Does anybody know which peripheral or API affects this pin functionality?