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OpenOCD was created by Dominic Rath as part of a 2005 diploma thesis written at the University of Applied Sciences Augsburg ( Since that time, the project has grown into an active open-source project, supported by a diverse community of software and hardware developers from around the world.

What is OpenOCD?

The Open On-Chip Debugger (OpenOCD) aims to provide debugging, in-system programming and boundary-scan testing for embedded target devices.

It does so with the assistance of a debug adapter, which is a small hardware module which helps provide the right kind of electrical signaling to the target being debugged. These are required since the debug host (on which OpenOCD runs) won’t usually have native support for such signaling, or the connector needed to hook up to the target.

Such debug adapters support one or more transport protocols, each of which involves different electrical signaling (and uses different messaging protocols on top of that signaling). There are many types of debug adapter, and little uniformity in what they are called. (There are also product naming differences.)

These adapters are sometimes packaged as discrete dongles, which may generically be called hardware interface dongles. Some development boards also integrate them directly, which may let the development board connect directly to the debug host over USB (and sometimes also to power it over USB).

For example, a JTAG Adapter supports JTAG signaling, and is used to communicate with JTAG (IEEE 1149.1) compliant TAPs on your target board. A TAP is a “Test Access Port”, a module which processes special instructions and data. TAPs are daisy-chained within and between chips and boards. JTAG supports debugging and boundary scan operations.

There are also SWD Adapters that support Serial Wire Debug (SWD) signaling to communicate with some newer ARM cores, as well as debug adapters which support both JTAG and SWD transports. SWD supports only debugging, whereas JTAG also supports boundary scan operations.

For some chips, there are also Programming Adapters supporting special transports used only to write code to flash memory, without support for on-chip debugging or boundary scan. (At this writing, OpenOCD does not support such non-debug adapters.)

Dongles: OpenOCD currently supports many types of hardware dongles: USB-based, parallel port-based, and other standalone boxes that run OpenOCD internally. See Debug Adapter Hardware.

GDB Debug: It allows ARM7 (ARM7TDMI and ARM720t), ARM9 (ARM920T, ARM922T, ARM926EJ–S, ARM966E–S), XScale (PXA25x, IXP42x), Cortex-M3 (Stellaris LM3, ST STM32 and Energy Micro EFM32) and Intel Quark (x10xx) based cores to be debugged via the GDB protocol.

Flash Programming: Flash writing is supported for external CFI-compatible NOR flashes (Intel and AMD/Spansion command set) and several internal flashes (LPC1700, LPC1800, LPC2000, LPC4300, AT91SAM7, AT91SAM3U, STR7x, STR9x, LM3, STM32x and EFM32). Preliminary support for various NAND flash controllers (LPC3180, Orion, S3C24xx, more) is included.

OpenOCD Web Site

The OpenOCD web site provides the latest public news from the community:

Latest User’s Guide:

The user’s guide you are now reading may not be the latest one available. A version for more recent code may be available. Its HTML form is published regularly at:

PDF form is likewise published at:

OpenOCD User’s Forum

There is an OpenOCD forum (phpBB) hosted by SparkFun, which might be helpful to you. Note that if you want anything to come to the attention of developers, you should post it to the OpenOCD Developer Mailing List instead of this forum.

OpenOCD User’s Mailing List

The OpenOCD User Mailing List provides the primary means of communication between users:


Support can also be found on irc: irc://

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