Firmware written against a schematic that has faults in it produces a board that fails mysteriously, on the bench, weeks later — and the debugging cost lands on the firmware, not the board.
Full firmware specification for a three-phase energy monitoring device, including a hardware review that surfaced design issues before they reached production — a reversed isolator channel, an oscillator marking off by a transposed digit, and a boot-strap conflict on a shared SPI pin.
Each fault was traced to its consequence and given a remedy: a dead CF1 output, a 0.037% systematic over-read that firmware can correct for, and an efuse-level fix for the GPIO12 strap conflict.