Why J-Link?

In case you wonder why GNU ARM Eclipse decided to provide support to SEGGER J-Link, the short answer is: because of J-Link EDU and of SWO. The long answer may include the following:

• wide processor support (there is probably no unsupported ARM processor in the entire galaxy, and if you find one in a remote quadrant, I’m pretty sure it’ll be shortly added to the list)
• it is a true multi-platform solution, providing drivers for Windows, OS X and GNU/Linux
• it comes with a standard GDB server implementation, compatible with existing ARM toolchains
• in addition to the classical JTAG protocol, it implements the new SWD protocol
• when SWD is selected, it is capable to sample the SWO pin, for trace messages and other ARM specific debugging
• it is fast, up to 15 MHz for JTAG clock and up to 7.5 MHz SWO sampling frequency for the new V9hardware (12 MHz JTAG / 6 MHz SWO for V8, and even up to 100 MHz SWO for the high-performance ULTRA+, PRO models)
• it supports all possible target voltages, from 1.2V to 5V
• in addition to the regular debugging functionality, it is also able to write the internal flash, and, even more, it uses a smart flash writing algorithm, to avoid useless writes if the flash blocks did not change
• it is a mature, proven product, with a great support team
• it provides an entire range of probes, J-Link, J-Link Pro, including a special priced version for educational use, the J-Link EDU (available from many distributors, for example from Farnell)

The J-Link was present on the JTAG market for many years, but, considering the initial prices, only the big companies could afford them. After a fierce fight against Chinese clones, sold for a fraction of the price, in 2012 SEGGER decided to introduce a low price version, J-Link EDU, restricted to educational and non-commercial usage, making it the JTAG probe of choice for open source GNU ARM development.

Overview

J-Link comes not only with a GDB server, but with a complete set of drivers and utilities, packed by SEGGER separately for each platform. The same distribution includes drivers for all J-Link probes, so installation is quite simple. The J-Link binaries are available from the SEGGER site. Download the file appropriate for your development platform. Please note that you need to have the J-Link serial number at hand, since the download site will ask for it. You can still download the J-Link software if you do not have the serial number, but you have to pass a multiple step confirmations sequence stating that you are not using illegal clones.

Documentation

The J-Link GDB server is documented in the UM08001 manual, available from the SEGGER J-Link page.

Windows

The Windows file is a ZIP archive, named like Setup_JLinkARM_V480.zip. After unpacking it, a Windows executable file is obtained, named like Setup_JLinkARM_V480.exe.

• double click it to start the installation process
• enter the administrative password
• accept the license
• accept the destination folder (C:\Program Files\SEGGER\JLinkARM_V480)
• accept the default USB driver

The result of the install is a folder (a new folder for each new version installed), and a set of driver files installed in the system folders, overwritten with each new install.

SEGGER Windows distribution.

Please note that on Windows, SEGGER provides both graphical interface and command line versions (having the names suffixed with CL) for most of their tools. For the J-Link plug-in it is recommended to use only the command line version of the  J-Link GDB server (JLinkGDBServerCL.exe).

OS X

The OS X download is an OS X package installer, like JLink_MacOSX_V480.pkg.

• double click it to start the installation process
• accept the license
• enter the administrative password, required to write in the global /Applications folder

The result of the install is a folder called /Applications/SEGGER/JLink/ (the same folder for all versions) where all executables and libraries are stored; please note that, as for many OS X applications, no other driver files are installed in the system folders.

SEGGER J-Link OS X distribution.

USB

On OS X, the USB subsystem automatically identifies and allows access to USB devices, without the need to maintain a manual list similar to the one used by UDEV in GNU/Linux. No other drivers or system configurations are required.

GNU/Linux

There are multiple packages available for GNU/Linux on the SEGGER download site, built as Debian/Red Hat packages, in 32/64-bit versions, or plain TGZ archives. Select the one appropriate for you system and use the specific tools to install the package. For example, on Ubuntu, to install the 64-bit .deb file, use the following command:

sudo dpkg -i jlink_4.80_x86_64.deb

The J-Link executables are installed in /usr/bin.

UDEV

The install procedure automatically adds /etc/udev/rules.d/99-jlink.rules to define the USB IDs of the J-Link devices. No other drivers are required.

Testing

To test if J-Link is able to connect to a specific board, you generally need to specify the interface (JTAG or SWD) and the device name. By default, J-Link GDBServer will try JTAG but if only SWD is wired (which is very common on custom hardware), you would need to specify the interface (-if SWD). The device name is needed for targets which require special handling on connect (e.g. due to silicon bugs which make auto-detection impossible). For a list of available device names, please refer to the SEGGER Supported devices page. Below is an example how to test a JTAG connection to a STM32F103 evaluation board (-device STM32F103RB) on OS X.

$ /Applications/SEGGER/JLink/JLinkGDBServer -if JTAG -device STM32F103RB
SEGGER J-Link GDB Server V4.80 Command Line Version

JLinkARM.dll V4.80 (DLL compiled Dec 20 2013 19:44:31)

-----GDB Server start settings-----
GDBInit file:                  none
GDB Server Listening port:     2331
SWO raw output listening port: 2332
Terminal I/O port:             2333
Accept remote connection:      yes
Generate logfile:              on
Verify download:               on
Init regs on start:            on
Silent mode:                   off
Single run mode:               off
------J-Link related settings------
J-Link script:                 none
Target interface:              JTAG
Host interface:                USB
Target endian:                 little
Target interface speed:        0kHz

Connecting to J-Link...
J-Link is connected.
Firmware: J-Link ARM V8 compiled Nov 25 2013 19:20:08
Hardware: V8.00
S/N: XXXXXXXXX
OEM: SEGGER-EDU
Feature(s): FlashBP, GDB
Checking target voltage...
Listening on TCP/IP port 2331
Connecting to target...
J-Link found 2 JTAG devices, Total IRLen = 9
JTAG ID: 0x3BA00477 (Cortex-M3)
Connected to target
Waiting for GDB connection...
^C

On Windows, to start the GDB server, use back-slashes in the path and the CL (command line) version:

C:\Program Files\SEGGER\JLinkARM_V480\JLinkGDBServerCL

On Ubuntu the command is simple:

/usr/bin/JLinkGDBServer

In all cases, the result should be similar to the one obtained on OS X.

The J-Link plug-in

If you successfully installed SEGGER binaries, you can proceed to the page documenting how to use the GNU ARM Eclipse J-Link hardware debugging plug-in.