hardware-interface-debug

# Hardware Interface Debug ## Overview Use this skill when firmware symptoms may actually come from board-level signals. Verify power, reset, clocks, pin mapping, voltage levels, and measured waveforms before treating the issue as a software bug. ## When To Use Use this skill when: - The issue involves power rails, reset, crystals, boot pins, connectors, level shifters, pull-ups, or signal integrity. - A peripheral or debug interface has no signal, wrong voltage, ringing, stuck line, or intermittent behavior. - The user has a schematic, board photo, oscilloscope capture, logic analyzer trace, or pinout question. Do not use this skill when the hardware path has already been verified and the issue is clearly inside firmware logic. ## First Questions Ask for: - Board/chip, revision, and affected interface. - Schematic snippet or pin mapping if available. - Expected signal and observed measurement. - Measurement tool: multimeter, oscilloscope, logic analyzer, current probe. - Power source and voltage levels. - Whether the issue is reproducible across boards. ## Workflow 1. Start with power and ground. Confirm rail voltage, sequencing, ripple, current limit, ground reference, and target voltage for debug probes. 1. Check reset and clock. Verify reset release, boot strap states, oscillator startup, clock output, and brownout/watchdog conditions. 1. Trace the signal path. Map MCU pin, package pin, board net, connector, level shifter, external device, and pull c...