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2 Debug Adapter Hardware

Defined: dongle: A small device that plugs into a computer and serves as an adapter .... [snip]

In the OpenOCD case, this generally refers to a small adapter that attaches to your computer via USB or the parallel port. One exception is the Ultimate Solutions ZY1000, packaged as a small box you attach via an ethernet cable. The ZY1000 has the advantage that it does not require any drivers to be installed on the developer PC. It also has a built in web interface. It supports RTCK/RCLK or adaptive clocking and has a built-in relay to power cycle targets remotely.

2.1 Choosing a Dongle

There are several things you should keep in mind when choosing a dongle.

  1. Transport Does it support the kind of communication that you need? OpenOCD focusses mostly on JTAG. Your version may also support other ways to communicate with target devices.
  2. Voltage What voltage is your target - 1.8, 2.8, 3.3, or 5V? Does your dongle support it? You might need a level converter.
  3. Pinout What pinout does your target board use? Does your dongle support it? You may be able to use jumper wires, or an "octopus" connector, to convert pinouts.
  4. Connection Does your computer have the USB, parallel, or Ethernet port needed?
  5. RTCK Do you expect to use it with ARM chips and boards with RTCK support (also known as “adaptive clocking”)?

2.2 Stand-alone JTAG Probe

The ZY1000 from Ultimate Solutions is technically not a dongle but a stand-alone JTAG probe that, unlike most dongles, doesn't require any drivers running on the developer's host computer. Once installed on a network using DHCP or a static IP assignment, users can access the ZY1000 probe locally or remotely from any host with access to the IP address assigned to the probe. The ZY1000 provides an intuitive web interface with direct access to the OpenOCD debugger. Users may also run a GDBSERVER directly on the ZY1000 to take full advantage of GCC & GDB to debug any distribution of embedded Linux or NetBSD running on the target. The ZY1000 supports RTCK & RCLK or adaptive clocking and has a built-in relay to power cycle the target remotely.

For more information, visit:

ZY1000 See:

2.3 USB FT2232 Based

There are many USB JTAG dongles on the market, many of them based on a chip from “Future Technology Devices International” (FTDI) known as the FTDI FT2232; this is a USB full speed (12 Mbps) chip. See: for more information. In summer 2009, USB high speed (480 Mbps) versions of these FTDI chips started to become available in JTAG adapters. Around 2012, a new variant appeared - FT232H - this is a single-channel version of FT2232H. (Adapters using those high speed FT2232H or FT232H chips may support adaptive clocking.)

The FT2232 chips are flexible enough to support some other transport options, such as SWD or the SPI variants used to program some chips. They have two communications channels, and one can be used for a UART adapter at the same time the other one is used to provide a debug adapter.

Also, some development boards integrate an FT2232 chip to serve as a built-in low-cost debug adapter and USB-to-serial solution.

2.4 USB-JTAG / Altera USB-Blaster compatibles

These devices also show up as FTDI devices, but are not protocol-compatible with the FT2232 devices. They are, however, protocol-compatible among themselves. USB-JTAG devices typically consist of a FT245 followed by a CPLD that understands a particular protocol, or emulates this protocol using some other hardware.

They may appear under different USB VID/PID depending on the particular product. The driver can be configured to search for any VID/PID pair (see the section on driver commands).

2.5 USB JLINK based

There are several OEM versions of the Segger JLINK adapter. It is an example of a micro controller based JTAG adapter, it uses an AT91SAM764 internally.

2.6 USB RLINK based

Raisonance has an adapter called RLink. It exists in a stripped-down form on the STM32 Primer, permanently attached to the JTAG lines. It also exists on the STM32 Primer2, but that is wired for SWD and not JTAG, thus not supported.

2.7 USB ST-LINK based

ST Micro has an adapter called ST-LINK. They only work with ST Micro chips, notably STM32 and STM8.

For info the original ST-LINK enumerates using the mass storage usb class; however, its implementation is completely broken. The result is this causes issues under Linux. The simplest solution is to get Linux to ignore the ST-LINK using one of the following methods:

2.8 USB TI/Stellaris ICDI based

Texas Instruments has an adapter called ICDI. It is not to be confused with the FTDI based adapters that were originally fitted to their evaluation boards. This is the adapter fitted to the Stellaris LaunchPad.

2.9 USB CMSIS-DAP based

ARM has released a interface standard called CMSIS-DAP that simplifies connecting debuggers to ARM Cortex based targets

2.10 USB Other

2.11 IBM PC Parallel Printer Port Based

The two well-known “JTAG Parallel Ports” cables are the Xilinx DLC5 and the Macraigor Wiggler. There are many clones and variations of these on the market.

Note that parallel ports are becoming much less common, so if you have the choice you should probably avoid these adapters in favor of USB-based ones.

2.12 Other...