The dap42 project is an open-source firmware and hardware design for an inexpensive, minimalist CMSIS-DAP based debug probe based on the STM32F042F6 in a TSSOP-20 package.

This project is currently in alpha - features generally do 80% of what's needed, but the last 20% is generally untested.

• Serial Wire Debug (SWD) access over CMSIS-DAP 1.0 HID interface (tested with OpenOCD and LPCXpresso)
• CDC-ACM USB-serial bridge
• Device Firmware Upgrade (DFU) over USB (detach-only, switches to on-chip DFuSe bootloader).

In general, the firmware can be uploaded over USB DFU without any extra hardware:

• Unflashed STM32F04x chips always start in the DFU bootloader.
• The bootloader button can be used to force the chip to start from the bootloader on reset (unless disabled)
• The firmware supports the DFU_DETACH request to switch to the bootloader
• When the firmware is reset by the watchdog, it enables the bootloader to ensure that firmware that consistently hard-faults or hangs can always upload new firmware.

The default method to upload new firmware is via dfu-util. The Makefile includes the dfuse-flash target to invoke dfu-util. dfu-util automatically detaches the dap42 firmware and uploads the firmware through the on-chip bootloader.

The dap42 firmware can experimentally also target the STM32F103 chip. The CDC UART is connected to PB11 (the SWIM pin on certain STLink/v2 knockoff designs) as an RX-only input.

To flash directly without a bootloader:

make clean
make TARGET=STM32F103
make TARGET=STM32F103 flash

The dap42 firmware has been tested with gdb and OpenOCD on STM32F042 (of course), STM32F103, and LPC11C14 targets.

In general, the probe can be used with OpenOCD just by specifying the cmsis-dap interface:

openocd -f interface/cmsis-dap.cfg -f your_config.cfg -c "some inline command"

Example OpenOCD configurations can be found under the openocd/ folder.

As of LPCXpresso 8.0.0, the default probe detection rules will not auto-discover generic CMSIS-DAP probes. To use the dap42 probe with LPCXpresso, you can modify the detection rules by editing lpcxpresso/bin/Scripts/probetable.csv in your LPCXpresso installation.

Add the following line to probetable.csv:

0x1209, 0xDA42, 64, 1, 0, 0, 0, "", 0x0000, -1

On Windows 10, the serial port works without requiring additional configuration.

For Windows XP through Windows 7, the DAP42CDC.inf .inf file can be used to load the generic USB serial driver.

On Mac OSX version 10.7 and later, the serial port should work without requiring any additional configuration.

On Linux, the serial port should be detected without requiring additional configuration. Depending on your distro settings, the modem manager may attempt to grab the serial port and use it as a modem. To prevent this, you can define a custom udev rule to ensure that the modem manager ignores the debugger.

ATTRS{idVendor}=="1209" ATTRS{idProduct}=="da42", ENV{ID_MM_DEVICE_IGNORE}="1"

• CMSIS-DAP 1.10 support
• Command queueing (command level, not packet level)
• Serial Wire Output (SWO) trace support
• Serial Line CAN (SLCAN) interface - Silent mode, RX only.
• Media Transfer Protocol (MTP) interface or Mass Storage Device (MSD) interface for drag-n-drop target firmware flashing

• Simultaneous USB-serial bridge and SWO trace using an STM32F042K6 in an LQFP-32 package with both UARTs pinned out.
• ESD protection
• Level-shifting/protective tri-state buffer between the probe and target SWD port.

The dap42 project was inspired by the Dapper Mime CMSIS-DAP proof-of-concept project.

The dap42 USB VID/PID pair is 1209/DA42, allocated through the pid.codes open-source USB PID program.

All contents of the dap42 project are licensed under terms that are compatible with the terms of the GNU Lesser General Public License version 3.

Non-libopencm3 related portions of the dap42 project are licensed under the less restrictive ISC license, except where otherwise specified in the headers of specific files.

See the LICENSE file for full details.