Segger JLink

J-Link is a series of powerful JTAG and SWD debug probes developed by Segger. They are widely used for debugging and programming ARM microcontrollers and other embedded systems. The J-Link debuggers are known for their speed, reliability, and compatibility with a wide range of development tools and environments, making them a preferred choice among embedded developers and hardware pentesters.

Features

• Multi-Interface Support

  • J-Link supports both JTAG and SWD protocols, allowing it to work with various microcontroller architectures.

• High-Speed Performance

  • It offers fast data transfer rates, enabling quicker debugging sessions and programming.

• Cross-Platform Compatibility

  • Works seamlessly with popular IDEs like Keil, IAR Embedded Workbench, and Eclipse.

• Extensive Support

  • Provides a comprehensive software package, including J-Link software and documentation, making it easier to get started.

Cheat Sheet

# Connect to J-Link device
JLinkExe.exe

# Connect to a target device (select device from pop up window)
connect

# Halt the target CPU
halt

# Reset the target CPU
r  # or 'reset'

# Reset and halt the CPU
reset halt

# Read memory at a specified address
mem32 <address> <count>  # Reads 32-bit words from memory

#Read complete flash and save it
savebin <filename.bin> <start address> <size>

# Write memory to a specified address
w1 <address> <value>     # Write 1 byte
w2 <address> <value>     # Write 2 bytes
w4 <address> <value>     # Write 4 bytes

# Load a binary file into the target device memory
loadbin <file> <address>

# Dump memory to a binary file
savebin <file> <address> <size>
savebin flash_dump.bin 0x08000000 0x00040000 #example

# Set a breakpoint
setbp <address>

# Clear a breakpoint
clrbp <address>

# Step through instructions
step

# Continue execution
go

# Exit J-Link Commander
q  # or 'exit'

Example Commands to Dump a Flash Chip Using J-Link

To dump a flash chip using J-Link, you can use the J-Link Command Line Interface (CLI) or the J-Link GDB Server. Below is an example using the J-Link CLI, which is part of the J-Link software package:

1. Open the Command Prompt (or Terminal on macOS/Linux).

2. Navigate to the J-Link installation directory where the CLI tool is located, usually found under C:\Program Files (x86)\SEGGER\JLink on Windows.

3. Connect the J-Link Debugger to your target device and power it on.

4. Run the J-Link Command Line Tool:

   JLink.exe

   
5. Connect to the Target Device: In the J-Link Command Line interface, use the following command:

   connect

   • Select the Device: Choose the specific device you are targeting (e.g., STM32F4xx).

   • Select Interface: Choose either SWD or JTAG based on your connection type.

   • Specify the Speed: Set the desired speed (default is usually fine).

   

   Successful cJTAG connection
6. Dump the Flash Memory:

   savebin <filename.bin> <start address> <size>

   • <filename.bin>: The name of the output file where the flash dump will be saved.

   • <start address>: The starting address of the flash memory you want to dump (e.g., 0x08000000 for STM32).

   • <size>: The number of bytes to dump (e.g., 0x00040000 for 256KB).

   Example:

   savebin flash_dump.bin 0x08000000 0x00040000

7. Exit the J-Link Command Line Tool

   exit

Resources

• J-Link Commander