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	SPI (flashrom)	I2C	AVR programming
RP2040	X	X	X	X	Planned	Planned
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>
GP10	SCLK
GP11	MOSI
GP12	MISO
GP13	nCS
GND	<ground>

On the RP2040, two USB CDC interfaces are exposed: the first is the UART interface, the second is for Serprog. If you have no other USB CDC devices, these will be /dev/ttyACM0 and /dev/ttyACM1, respectively.

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). If you want to get stdio readout on your computer, connect GP0 to GP5, and GP1 to GP4.

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.

For Serprog, use the following flashrom options (if /dev/ttyACM1 is the USB serial device on your machine corresponding to the Serprog CDC interface of the Pico):

flashrom -c <flashchip> -p serprog:dev=/dev/ttyACM1:115200 <rest of the read/write cmd>

Different serial speeds can be used, too. Serprog support is techincally untested, as in it does output the correct SPI commands as seen by my logic analyzer, but I don't have a SPI flash chip to test it on.

License

TinyUSB is licensed under the MIT license.

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

libco is licensed under the ISC license

TODO

• CMSIS-DAP JTAG implementation
• Flashrom/SPI support using Serprog
• UART with CTS/RTS flow control
• I2C support by emulating the I2C Tiny USB
  • Expose RP2040-internal temperature ADC on I2C-over-USB bus?
  • Does SMBus stuff need special treatment here?
• Maybe add some way of reconfiguring features while the device is running. Eg. CTS/RTS enable/disable, temperature ADC I2C address, ...
  • Maybe use the Serprog USB serial interface for this, with some extension commands not typically used for Serprog.
• AVR programming (USBavr emulation?)
• Renesas E7-{0,1,2} programming thing????
  • Renesas tell us how this works pls
• Maybe steal other features from the Bus Pirate or Glasgow or so
  • 1-wire? Never seen this one in the wild
  • MIDI? Feels mostly gimmicky...
  • PS/2? Hmmmm idk
  • HD44780 LCD? See MIDI
  • CAN? If I'd first be able to find a CAN device to test it with, sure