Dapper Mime

This unearths the name of a weekend project that I did in 2014. Both then and now, this is a port of ARM's CMSIS-DAP code to a platform without the need for an expensive proprietary compiler and USB drivers.

Whereas the original code used ST's STM32 USB drivers, this new iteration uses TinyUSB, an open source cross-platform USB stack for embedded systems.

Variants

Most TinyUSB supported MCUs can run this code; a subdirectory under bsp needs to be added for the "BOARD" name with a DAP_config.h to control the SWD/JTAG GPIOs and a unique.h to provide unique serial number (if any) and prefix to the USB product name.

Already added BOARD variants include:

For BOARD=raspberry_pi_pico, this project results in a standards-based CMSIS-DAP alternative to the approaches suggested in Chapter 5 and Appendix A of Getting Started with Raspberry Pi Pico. This uses two RP2040 boards (see wiring loom shown in Figure 34 of Appendix A) where one RP2040 is the debugger and the other RP2040 is being debugged. The instructions in Chapter 5 apply, except no Raspberry Pi is needed.

Alternatively, a special one RP2040 “Raspberry Pi Pico” variant is available here.

For BOARD=stm32f072disco, the inexpensive 32F072BDISCOVERY evaluation board can be used as a CMSIS-DAP SWD debugger.

Building

After initially downloading this project's code, issue the following command to download TinyUSB and CMSIS_5 code:

git submodule update --init --recursive

Follow the TinyUSB build instructions available here, but issue the make command in the base directory of Dapper Mime.

Note that each TinyUSB board name being targeted needs a corresponding subdirectory under the Dapper Mime ./bsp/ subdirectory and a customized version of DAP_config.h for the target.

Alternatively, one can compile with CMake:

mkdir cmake-build && cd cmake-build
cmake -DBOARD=raspberry_pi_pico -DFAMILIY=rp2040 -DCMAKE_BUILD_TYPE=Debug ..

If you have the Pico SDK installed on your system, and the PICO_SDK_PATH environment variable is specified properly, you can omit the --recursive flag in the git submodule invocation (to avoid many many git clones), and pass the -DUSE_SYSTEMWIDE_PICOSDK=On flag to CMake, too.

Usage

These microcontrollers support the following protocols:

MCU	SWD	JTAG	UART
RP2040	X	X	X
STM32F072B Discovery	X		X

The original repository (Dapper Mime) supported only SWD and UART, and worked for these two boards. This fork focusses on adding more protocols, but the author of this fork only has a Raspberry Pi Pico.

The pin mapping for the RP2040 is as follows:

Pin number	Usage
GP0	stdio UART TX
GP1	stdio UART RX
GND	<ground;>
GP2	SWCLK/TCK
GP3	SWDIO/TMS
GP4	UART TX
GP5	UART RX
GND	<ground;>
GP6	TDI
GP7	TDO
GP8	nTRST
GP9	nRESET
GND	<ground;>

The UART pins are for connecting to the device to be debugged, the data is echoed back over the USB CDC interface (typically a /dev/ttyACMx device on Linux).

In SWD mode, the pin mapping is entirely as with the standard Picoprobe setup, as described in Chapter 5 and Appendix A of Getting Started with Raspberry Pi Pico

In JTAG mode, TCK and TMS have the same pins as SWCLK and SWDIO, respectively, TDI and TDO are on the next two consecutive free pins.

In your OpenOCD flags, use -f interface/cmsis-dap.cfg. Default transport is JTAG, if OpenOCD doesn't specify a default to the probe.

License

TinyUSB is licensed under the MIT license.

ARM's CMSIS_5 code is licensed under the Apache 2.0 license.

TODO

• Flashrom/SPI support using Serprog
• I2C support by emulating the I2C Tiny USB
• AVR programming (USBavr emulation?)