UART Shell

UART AutoShell

UART AutoShell is a lightweight serial console that lets you interface with any TTL-level device directly from the Cardputer’s built-in keyboard and IPS display. Ideal for debugging or gaining root shell access on embedded targets like routers or IP cameras, it can auto-detect the baudrate or let you pick one manually from a keyboard-driven menu.

Features

• Automatic baud-rate scan across 300 – 115 200 bps
• Manual baud-rate selection menu
• Non-blocking, per-character echo to both UART and display
• Smooth line-by-line scrolling on the 240 × 135 px screen
• One-keystroke exit (`) back to the main menu

Usage

First you need to connect to an equipment with UART using pin : G1/RX // G2/TX // GND.
Connect the device with cross RX/TX : Cardputer RX go to TX device and Cardputer TX go to RX device.

1. Flash the firmware to your Cardputer.
2. Boot the device and open the main menu.
3. Select UART AutoShell. The baud-rate picker appears.
4. Navigate with ; (up) and . (down). Press Enter to select.
5. Choose “Auto-detect” or a fixed rate. During auto-detect a spinner shows progress.
6. The GPS on UART2 is released and UART1 starts at the selected speed.
7. Type commands – each character is echoed; press ` to quit.

Key bindings

Key	Function
Enter	Send CRLF and begin a new prompt
Del	Send backspace (0x08)
`	Quit AutoShell
;	Menu up (baud picker)
.	Menu down (baud picker)

Auto-detection heuristic

Each candidate baud-rate is tested for 1.2 s. The scan accepts a rate when

• ≥ 30 bytes are received, and
• printable bytes ≥ 60 % of the total.

A rotating spinner shows progress during the scan.

Scrolling implementation

Whenever the cursor would move below height – LINE_H, the display is scrolled up by one text line using scroll(0, -LINE_H) and the cursor is repositioned. This avoids frame-buffer copies and keeps scrolling smooth.

Ressources

• Hardware Hacking 101 – Getting a root shell via UART (Riverloop Security)
• How to Use Serial Console Recovery for OpenWrt (Instructables)
• Failsafe Mode & Factory Reset (OpenWrt Wiki)
• Serial Console / port.serial (OpenWrt Wiki)

Cameras & IoT

• Exploiting UART to Gain Shell Access on a Security Camera (Medium)
• Shell access over UART – Teardown D-Link DCS-932L (Don’t Panic! blog)
• Accessing & Dumping Firmware Through UART (CyberArk Labs)

Videos

• Finding UART & Getting a Root Shell on a Linux Router
• Hacker’s Guide to UART Root Shells (IoT devices)