Thanks, adding a 10k pull-down on SD1 enabled the USB bootloader.I've got the schematics, thanks.
Make sure that QSPI SD1 is not pulled-up by FPGA at least for 10ms after Reset, otherwise it will enter in UART bootloader mode instead of USB.
RP2350's pulls are very weak (around 60k equivalent) and can be easily overridden even by a 10k one (like I did from my logic analyzer).
Cyclone 10 has stronger pulls despite they call them 'weak'.
I would check the signals with an oscilloscope.
GPIO24 has nothing to do with the boot process, and by default is pulled down at reset (and isolated from the core) like any other GPIO.
It just happens to be available sense the voltage on VBUS.
USB is perfectly functional without it.
The rework is a little tedious and near the limit of my soldering skills. Is there any way to bypass this check? I’m wondering if I could create an OTP boot that skips this and then jumps back to the BootROM. Any ideas for a software work around?
Statistics: Posted by steieio — Tue Nov 04, 2025 3:45 am