I am trying to boot my Pico from an external NOR flash module, but I'm not sure how to do it. The QSPI pins on the RP2040 look to be used already, is there any way I can access these externally or set up another interface? Theoretically, XIP would work, but I'm even more confused on how to use it. Any help would be great.
XIP is only available on the QSPI interface. You have to boot first from the NOR flash on the QSPI interface or via USB programming. You can't run code from an external flash module, but you could copy code from that flash module to the internal SRAM first and then execute that.