2.3.3 Connect via Serial Port
Serial port access is the emergency method when SSH is unavailable on the board: by directly reading the board's console through UART, you can view boot logs, log into the board’s shell, and debug U-Boot and kernel startup. Serial access provides only terminal capabilities and does not support file transfer, remote desktop, or remote IDE.
Applicable Scenarios
| Scenario | Solved by Serial |
|---|---|
| Board is bricked and stuck at logo during boot | Read boot logs to locate the issue |
| Misconfigured network prevents SSH connection | Enter console to restore correct configuration |
| Need to view dmesg or kernel logs | Full kernel output available |
| Debugging U-Boot or kernel boot process | Only viable method |
| Need to transfer files, view desktop, or use remote IDE | Not supported by serial; requires SSH |
Step 1: Wiring
The physical location of the serial port and default baud rate vary by board model (these three parameters differ—always configure according to your specific board model; otherwise, you’ll see garbled text):
| Board Model | Serial Port Location | Default Baud Rate |
|---|---|---|
| RDK X3 | UART2 on the 40-pin GPIO header | 921600 |
| RDK X5 | Onboard micro-USB debug port (built-in USB-UART bridge) | 115200 |
| RDK S100 | Onboard USB-UART (Type-C debug port J16) | 921600 |
All boards use
8N1configuration with no flow control.
RDK X5 and RDK S100 include a built-in USB-UART bridge—simply connect to your PC using a standard USB data cable. For RDK X3, you need a USB-to-TTL module, cross-connecting the module’s RX/TX pins to the board’s UART pins.
Step 2: Select Serial Access in Studio
Open the desktop client and click Add Device at the top. In the pop-up window, choose USB Serial Debugging and fill in the following fields:
| Field | Default Value | Description |
|---|---|---|
| Serial Device | (Automatically listed by Studio) | Typically /dev/tty.usbserial-XXXX on macOS; /dev/ttyUSB0 on Linux; COM3, etc., on Windows |
| Baud Rate | 115200 | Default in Studio UI; switch to 921600 for RDK X3 and RDK S100 |
| Data / Parity / Stop Bits | 8 / N / 1 | Standard serial configuration |
Step 3: Connect
Click Connect. The terminal will immediately display the board’s console: if the board is already running, you’ll see a shell prompt; if the board is booting, you’ll see boot logs.
Common Serial Issues
| Symptom | Possible Cause | Solution |
|---|---|---|
| Serial device list is empty | Driver not installed or cable not properly connected | macOS and Linux are usually driver-free; install CH340/FTDI drivers on Windows |
| Garbled characters appear after connection | Baud rate mismatch | Use 921600 for X3/S100 and 115200 for X5; if still garbled, try 1500000 |
| Characters appear but pressing Enter has no response | Incorrect line-ending setting | Studio defaults to LF; try switching to CRLF |
| Only a few lines appear during boot then stops | Incomplete UART connection or console hijacked | Check jumpers; some kernels may redirect console output to another channel |
Emergency Example: Board Fails to Boot into System
Follow these steps to troubleshoot boot failure:
- Connect the serial cable and power off the board.
- In Studio, start listening on the serial port (connect first).
- Power on the board.
- When you see the U-Boot countdown, press any key to interrupt.
- Once in the U-Boot shell, you can:
setenv bootargs ...to modify boot arguments- Choose an alternative kernel to boot
- Flash firmware via TFTP (advanced)
If you can’t interpret U-Boot output, copy the entire boot log into AI Dock—AI will analyze exactly where the boot process is failing.
Next Steps
Once the board boots successfully, switch to 2.3.2 Connect via SSH to restore full functionality (remote terminal, file management, IDE, remote desktop).