Single-ended LVCMOS12/15 input on the Y1 (slave) site of an HP-bank
IOB18 tile was missing. nextpnr emits it for LVCMOS15 inputs on the
N pin of a diff pair; fasm2frames failed with FasmLookupError
(blinky/hdmi-stlv7325, RIOB18_X95Y25). Bit value mirrors the
LVCMOS12_LVCMOS15_LVCMOS18.IN variant at the same site, matching the
bit-identity of the Y0 with/without-LVCMOS18 pair (verified in both
families).