Quick diagnostic pass
Run this sequence before changing higher-level firmware logic.
- Confirm voltage level compatibility between MCU and adapter.
- Validate TX/RX crossover and common ground.
- Verify baud, data bits, parity, and stop bits on both sides.
- Capture raw serial output to check framing and corruption patterns.
- Review buffer handling for overflow, newline handling, and blocking writes.
Failure signatures
- Random symbols usually indicate framing mismatch or timing drift.
- Clean boot banner then silence often points to task starvation or blocking IO.
- Intermittent output under load can indicate flow-control assumptions or ISR timing issues.
Preventive baseline
Document a known-good serial profile for every board revision and keep it in bring-up notes.