Pinout
With RTL on the iCE40
The wafer names IOB_6a, IOT_8b… as well as the pin number ICE_2, ICE_3, ICE_4… can be used from the RTL by picking them from this PCF file.
For Amaranth, until this gets upstreamed, the various board resources including its pins are defined on pico_ice.py.
With code on the RP2040
The FPGA pins and other signals are defined in pico_ice.h.
The PMOD pins can also be accessed from pmod.h and ice_pmod.h.