Using GPIO9 is bad? Causes flash boot fail?

[markxr]

Hi,

I've designed my own board with the ESP32-PICO-D4. It does not boot off flash, instead it just gives me the infamous "flash read err, 1000" error. However, I was able to put it into serial boot mode and write to the flash

I checked my soldering carefully and I really don't think I've created any short circuits etc,

My current hypothesis is that attaching a PCB track to GPIO9 causes it to fail (I will test this later),

GPIO9 is the master SDIO DAT2 pin which is, according to the datasheet, not internally used and not one of the unusable pins. However, I wonder if there is a problem with too much capacitance on the track when the chip is sending out signals during boot or something?

Is that possible? I will try to get an oscilloscope on that pin to see if it's wiggling.

[ESP_Sprite]

Strange, as far as I can tell you're right in that GPIO9 should be available to use. Are you sure it's not accidentally shorted to one of the adjacent pins? It's right next to GPIO17, which is a flash pin, for instance.