LattePanda Iota RP2040 Boot Freeze: GP1 Pull-up Conflict, USB Deadlock,y

Question

Hi everyone, I'm having a strange problem with the RP2040 integrated into the LattePanda Iota and would like to understand the technical reason behind this behavior.

When I connect my custom expansion board, the RP2040 co-processor i snot recognized as USB by windows on boot.

The blue LED lights up but, the microcontroller can't enumerate itself as a USB device to the Intel main processor, preventing any communication or reprogramming.

Investigating with a multimeter, I noticed that the GP1 pin, which on my board has a 10kΩ pull-up resistor to 3.3V, stops at around 2.7V during boot.

This value shows that maybe a voltage divider is formed between the external pull-up and the RP2040's internal pull-down resistor of around 45kΩ, meaning the pin is read as a stable high.

My question is: does anyone know exactly what the RP2040's factory firmware or bootrom does on that pin in the very first moments of boot?

Why does a high level on GP1 (which on the silicon corresponds to pin 3 and handles functions like UART0 RX or SPI0 CS) manage to completely stall the microcontroller before the USB stack even activates?

the RP2040 was programmed with Firmata firmware. If I leave the pin floating (not connecting my board, the rp2040 starts properly).

Any technical explanation on what triggers this hang in the boot sequence or internal pin management would be greatly appreciated.

Thanks for your help

Jason.Miao · Answer

RP2040's bootrom hard-codes GPIO0–3 as the QSPI flash interface during startup, and GPIO1 is the CLK line. Your 10kΩ pull-up fixes the pin at 2.7V (logic high against the ~50kΩ internal pulldown), so the clock never drops and the QSPI read fails. The bootrom retries instead of falling through to USB boot, which is why the USB stack never comes up. The 2.7V is well above the RP2040's Vih threshold (~2.0V), so the pin reads as a stable high. Move the pull-up to GP4 or higher, swap it for 100kΩ+ so the divider drops below Vil, or remove it entirely. The RP2040 datasheet calls out GPIO0–3 as "QSPI boot pins" and warns that external loading on these lines can interfere with flash access.