swddude is very young pre-alpha software. Caveat downloader.

swddude is a collection of simple tools for programming and using ARM Cortex microcontrollers, such as the Cortex-M0 and M3, using the SWD protocol.


Larger ARM microcontrollers have JTAG interfaces. OpenOCD and friends already do a great job flashing these micros. But for smaller parts, such as the LPC11xx/LPC13xx series, ARM has defined a new low-pin-count debug interface called SWD. OpenOCD doesn't yet support SWD. In fact, when we started writing swddude, no software on Mac or Linux could do what we wanted!

It's a shame not to be able to use these powerful little microcontrollers, so we wrote swddude to scratch this itch.

What Can It Do?


  • swddude itself can flash code onto the NXP LPC11xx (Cortex-M0 based) and LPC13xx (Cortex-M3 based).
  • swdprobe can interrogate a SWD-compatible chip and dump information about what it finds. This is useful when adding support for new chips to swddude.
  • swdhost provides semihosting I/O for an attached microcontroller. With semihosting, embedded software can send printf-style messages to a host computer through the debug connection -- no UART required.
  • swddump extracts the contents of Flash from a supported microcontroller.

We're working to extend the tools to support more microcontroller varieties. Specifically, we're focusing on microcontrollers without JTAG ports -- devices that can't be easily added to OpenOCD (yet).

How Do I Use It?

You'll need a supported programmer and, of course, a supported microcontroller with a SWD interface. Currently swddude supports using the Bus Blaster (v2.5 programmed with the KT-link compatible CPLD configuration) or any FTDI development board with an FT232H or FT2232H chip that has been wired to the SWD lines of your microcontroller.

Wire up your micro using the configuration described in swd_mpsse.h.

Install libusb 1.0 and the libusb-compat package. The version supplied by your package manager (apt, Homebrew, etc.) should be fine.

Build a recent version of libftdi. As of this writing, you must build libftdi from HEAD -- the released version (0.20) still uses the legacy libusb 0.1 APIs and is incompatible with swddude.

After checking out swddude, build it like so:

$ cd swddude/source
$ make swddude release

This will deposit a swddude binary in swddude/source/release.

To program your microcontroller, you'll need to have your desired firmware in binary format -- not ELF, and not Intel hex. Assuming it's in a file called firmware.bin, you run:

$ swddude -flash firmware.bin -fix_lpc_checksum

This will default to the um232h programmer (FTDI's FT232H development board) configuration. If you are using a Bus Blaster, you should add -programmer bus_blaster to the command line above.

That last option, -fix_lpc_checksum, adds the vector table checksum expected by the NXP LPC series. Without it, your firmware won't run! If some other tool has already written the correct checksum into your firmware, you can omit that option.

Status and Known Issues

These boards are known to work:

  • LPCxpresso LPC1114.
  • LPCxpresso LPC11C24.
  • LPCxpresso LPC1343.

Note that the LPCxpresso boards will only work if you disable the proprietary LPC-Link programming device on the board. On newer boards, you can do this by clearing solder jumpers between the two sections of the board; older boards make you physically cut traces in the same position.

Known issues:

  • Error reporting is not great. Most failures just print a stack trace, which isn't helpful if you're not familiar with the source code. In general, it's worth retrying at least once -- sometimes the SWD communications just need to be reset.
  • swddude makes no attempt at identifying the chip it's programming. If you try programming an unsupported chip, it may do very bad things -- there is no safety net.
  • On the LPC1343 specifically, the SWD interfaces sometimes gets "stuck" and requires a power-cycle. This will show up as failures very early during communication (often referencing the IDCODE register).

Brief Tour of the Source

The source code contains the following top-level directories:

  • build: Anton Staaf's build system.
  • libs: Anton Staaf's support libraries, several of which we use. (We currently include more than we strictly need here.)
  • source: swddude and friends.

The source tree uses git's submodule feature aggressively. If you check out swddude using a simple git clone, you'll be left with empty directories that won't build. You can fix this by running

git submodule update --recursive

Alternatively, you can make this happen automatically when you clone, like so:

git clone --recursive ${git_url}