🛠 Step through RA4M1 code with a SWD debugger

Goal

Go beyond printf debugging: the UNO R4 Minima exposes an onboard debug connector so you can attach a hardware debugger, halt the Cortex-M4, inspect registers and step through the RA4M1 while it runs.

How

1. Wire a debug probe to the board's SWD connector: SWDIO, SWCLK, GND and 3.3 V (the store page advertises connecting an external debugger to monitor the inner workings).
2. Use a GDB-based toolchain: a CMSIS-DAP probe with OpenOCD + arm-none-eabi-gdb, a J-Link, or the Arduino IDE debugger integration for the Renesas core.
3. Set a breakpoint in loop, run, and watch variables, the peripheral registers and the call stack.

Why it matters

Hard-faults, runaway ISRs and peripheral misconfiguration on a 48 MHz Cortex-M4 are painful over Serial only; with SWD you get cycle-accurate truth.

Gotchas

• Halting the core also stalls USB: the host may see disconnects while stepping.
• If attach fails, try connect-under-reset and double-check SWDIO/SWCLK are not swapped.