UART-CLI for debugging MCU firmware

UART-CLI: Essential Debugging Tool for Embedded Firmware

UART-CLI gives you direct access to firmware status via a serial interface. It lets you check GPIO states, software versions, and hardware configs without fancy gear. Unlike JTAG or SWD, UART just needs basic adapters like CP2102 and a terminal like Tera Term or PuTTY.

For remote devices, CLI stays indispensable. If your wireless stack (LoRa, CAN, Ethernet) breaks after a commit, UART commands pinpoint the issue in minutes, skipping hours of GDB debugging.

Advantages Over Traditional Debugging

CLI slips into debug builds and gets stripped from release versions with a single Makefile flag (Y/N). It doesn't bog down production firmware or hurt performance.

Tricky stacks like LTE/IP or Bluetooth get debugged with simple tools: Ethernet via UART, GPIO with a multimeter. CLI opens a "conversation" with the firmware—dynamic log levels (INFO, DEBUG, PARANOID) per module stop log floods in big firmwares (320 kB, 80+ components).

UART-CLI works over any channel: CAN (ISO-TP), UDP, LoRa—with a host console utility and optional traffic compression.

Key Use Cases

• Multi-core MCUs: Core0 via JTAG/GDB, Core1/2 via separate UARTs (e.g., SPC58NN84E7RMHBR).
• Hang Detection: No echo on Enter signals a freeze without a heartbeat LED.
• Automation: Run tests, log serial numbers, encryption keys.
• Pin Backup: When JTAG/SWD pins are tied up by relays/buttons, UART stays free (BOOT pins).

| Interface Comparison |

|----------------------|

| Interface | Wires | Cable Length | Cost | ESD Resistance |

| UART-CLI | 4 (Rx/Tx/GND/VDD) | >1 m | Low | High |

| JTAG/SWD | 20 | <40 cm | High (7k RUB–5k EUR) | Low |

20+ Practical UART-CLI Use Cases

• Dump GPIO states with one command.
• Query firmware/hardware versions.
• Run module tests by substring (e.g., "i2c").
• Verify DAC (sine wave at frequency), FatFS dump.
• Diagnose interrupts.
• Load non-volatile configs (transceiver modulation).
• Simulate protocols/API for testing.
• Debug without symbols (-g3) due to NOR-Flash limits.
• Quick reboot vs. 2 minutes in Eclipse Terminate&Relaunch.
• Copy-paste in TeraTerm (impossible in GUI configurators).
• Non-IT staff using PDF guides.
• Smoke test: Enter → cursor → firmware alive.

CLI replaces JTAG in 80% of cases, except total hangs.

Key Takeaways

• UART-CLI is a minimalist gateway to firmware, like an ISA microprocessor bus.
• Debug complex stacks (Ethernet) with simple tools (UART), hierarchically.
• Dual mode: logs + interactive commands ease bus/DMA load.
• Scales to any interface without GUI.
• Saves time/money vs. JTAG in production.

— Editorial Team