Analyze the principles and differences between J-Link, J-Trace, and Open JTAG

J-Link, J-Trace, and Open JTAG are all used to debug programs (of course, there are other tools for debugging, such as ICE). J-Link and J-Trace are open source projects of SEGGER, whose goal is to enable embedded developers to use open hardware and software systems to burn, verify, and debug through the JTAG interface. They are all based on the JTAG debug interface protocol.

1. Working Principle

To debug ARM, you must follow the ARM debug interface protocol, and JTAG is one of them. When emulating, IAR, Keil, ADS, etc. all have a common debug interface, and RDI (RDI interface is the debug interface standard proposed by ARM, mainly used for JTAG emulation of ARM chips) is one of them. So how do we complete the conversion from RDI to ARM debug protocol (JTAG)? There are two ways to do this:

(1) Write a service program on the computer to parse the RDI commands in keil, ads, and iar into the relevant JTAG protocol, and then send it to your target board through a physical conversion interface (note that this conversion is only a conversion on the electrical physical layer, just like the function of RS232). H-JTAG is like this. The hardware of H-JTAG is just a physical level conversion interface, so it is very simple. The H-JTAG software installed in the computer is the service program mentioned above, which is responsible for protocol conversion.

(2) Another way is to make a board, use this board to directly receive debugging commands from keil, ads, iar and other software, and use this board to convert rdi->jtag protocol. Then communicate with the target board, which is the working principle of jlink. (This also realizes the USB to JTAG protocol.)

One post said: "Boss, both are done with software, but the software is placed in different places (one is on the computer, the other is in the simulator). The real hardware, like JTRACE, is implemented with FPGA. In essence, it is still a process from software to hardware."

2. Differences between J-Link and J-Trace

I was recently reading Page 12 of "J-Link/J-Trace User Guide (UM08001)" and found that the article explained the difference between JLink and JTrace, which is easy to understand. The excerpt is as follows:

J-Link

JTAG emulator for ARM cores

USB driven JTAG interface for ARM cores.

J-Trace

JTAG emulator for ARM cores

USB driven JTAG interface for ARM cores with

Trace memory. supporting the ARM ETM (Embed-

ded Trace Macrocell).

The ARM Keil Tools official website (http://www.keil.com/pr/article/1141.htm) is more detailed, excerpted as follows:

The SEGGER J-Link is a USB to JTAG adapter supporting ARM7™, ARM9™ and Cortex™-M3 processor based devices with JTAG speeds of up to 12MHz. It interfaces to all evaluation boards and target hardware using a standard 20-pin or 14-pin (optional) JTAG connector.

The SEGGER J-Trace is a combined unit offering real-time trace and JTAG debugging for all ARM7 and ARM9 devices with an integrated ETM (Embedded Trace Macrocell). An integrated 2MB trace buffer enables high speed instruction and data trace at speeds of up to 200MHz, connecting to the target device via a 38-pin Mictor cable. J-Trace also includes a J-Link interface for standard JTAG target debugging via a 20-pin connector.

Trace information from J-Trace is displayed in dedicated windows, providing a seamless interface with other μVision debug and analysis tools.

J-Link is part of several starter kits from various vendors and is indentical with SAM-ICE (from Atmel) and mIDAS-Link (from Analog Devices). With direct J-Link support users can now easily begin taking advantage of the unique and advanced features of RealView MDK compared to other tool offerings and starter kits.

RealView MDK is available from Keil or your local Keil distributor. J-Link and J-Trace are available from SEGGER Microcontroller and its world wide sales channels.

I saw a post in the forum that gave a brilliant answer to the difference between J-Link and J-Trace, as follows:

J-Link is like a camera, you can only see the debugging information when the program stops (at a breakpoint), through the JTAG/SWD interface; J-Trace is like a video recorder, which can record and replay the entire debugging interface, through the ETM interface. Recently, some Cortex-M3 chips support the SWO interface, which is like a high-speed continuous shooting camera. If the sampling interval is small, it looks a bit like Trace. This debugging function has been supported in J-Link v7 and EWARM v5.30.

3. Differences between J-Link and Open JTAG

As mentioned above, both are used to debug programs, and both implement the USB to JTAG protocol function, that is, use USB to connect to the host, use JTAG cable to connect to the JTAG port of the board, and the conversion between them is done through J-Link or Open JTAG conversion. In addition, J-Link is generally an independent component, while Open JTAG is generally integrated into the board.

4. J-Link GDBServer and Open OCD

openOCD is a host computer program (a computer that people can directly issue control commands to, usually a PC. Corresponding to the lower computer). jlink gdbserver and openocd are the same thing, both play the role of a gdb server, used to interpret the debugging signals from arm-elf-gdb and control the hardware (Jlink or openjtag)