ESP8266 Community Forum

- Tue Jan 07, 2020 4:48 pm #85179 Hi,

The GPIO Pins define what boot option is choosen:


Is this handled in the bootloader? Can this be changed?

My problem is that I use GPIO15 also as digital Input. Sometime when I have an external reset (RST PIN) the GPIO15 is still high. So my esp8266 tries to boot from sd card and crashs. In this case I'm unable to reset the esp8266 again. the only thing that helps is a power down.

My idea is to change the bootloader that the GPIO15 pin is ignored at boot. Is this possible?

- Wed Jan 08, 2020 4:44 am #85184 My understanding is that the inspection of the 3 GPIO pins to determine the initial start up procedure takes place in the primary boot code which is in internal ROM in the device and is not changeable. This also ensures that is impossible to brick the device by changing this part with code that breaks the start up and always allows updating the normal firmware.

It is normally best to utilise these pins as outputs where possible so that pull up / down resistors may be used to guarantee their state at reset. The pins are reverted to inputs during reset and then once the boot sequence is correctly started the app code can safely set them to be outputs.

- Sun Apr 12, 2020 5:14 am #86453 +1