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	Other stuff
RP2040	X	X	X	X	X	Planned
STM32F072B Discovery	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	Usage	Pin number
GP0	stdio UART TX		VBUS
GP1	stdio UART RX		VSYS
GND	<ground>	<ground>	GND
GP2	SWCLK/TCK		3V3 EN
GP3	SWDIO/TMS		3V3 OUT
GP4	UART TX		ADC VREF
GP5	UART RX		GP28 / ADC2
GND	<ground>	<ground>	GND / AGND
GP6	TDI		GP27 / ADC1
GP7	TDO		GP26 / ADC0
GP8	nTRST		RUN
GP9	nRESET		GP22
GND	<ground>	<ground>	GND
GP10	UART CTS	SCL	GP21
GP11	UART RTS	SDA	GP20
GP12	MISO		GP19
GP13	nCS		GP18
GND	<ground>	<ground>	GND
GP14	SCLK		GP17
GP15	MOSI		GP16
<end>	<bottom>	<bottom>	<end>

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 intefaces, 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 of this program on your computer, connect GP0 to GP5, and GP1 to GP4, or alternatively, use the USE_USBCDC_FOR_STDIO CMake flag, which adds an extra USB-CDC interface for which stdio is used exclusively, while disabling stdio on the UART.

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.

The I2C-Tiny-USB functionality can be used as follows: first, load the i2c-dev and i2c-tiny-usb modules (for now you need a patched version of the latter, can be found in the i2c-tiny-usb-misc/ folder in this repo). Then you can use the I2C USB bridge as any other I2C device on your computer. For example, the i2cdetect, i2cget and i2cset tools from i2c-tools should all work. You can find which I2C device corresponds to the I2C-Tiny-USB, by running i2cdetect -l:

$ sudo i2cdetect -l
[...]
i2c-1	i2c       	i915 gmbus dpb                  	I2C adapter
i2c-8	i2c       	Radeon i2c bit bus 0x95         	I2C adapter
i2c-15	i2c       	i2c-tiny-usb at bus 001 device 011	I2C adapter  # <---- !
i2c-6	i2c       	Radeon i2c bit bus 0x93         	I2C adapter
i2c-13	i2c       	AUX C/DDI C/PHY C               	I2C adapter
[...]

If the board/MCU has a builtin temperature sensor, a fake I2C device on the bus can optionally be enabled to use it as a Jedec JC42.2-compliant temperature sensor (the exact sensor emulated is the Microchip MCP9808). To have it show up in sensors, do the following (with BUSNUM the number from the above i2cdetect -l output):

$ sudo modprobe jc42
$ echo "jc42 0x18" | sudo tee /sys/bus/i2c/device/i2c-BUSNUM/new_device
$ sudo sensors

Temperature readout is currently not really working.

Runtime configuration

Several settings can be applied at runtime, using the dmctl Python script. Settings are communicated over the Serprog USB serial port.

The currently implemented options are:

• support: tells you which features this implementation/board supports
• ctsrts: Enable/disable CTS/RTS-based hardware flow control for the UART port
• i2ctemp: Get or set the I2C address of the fake I2C device of the temperature sensor. Use 0 for getting the value, 0xff for disabling, and any other for setting the address. The I2C device emulated is an MCP9808.

usage: dmctl [-h] [-v] [--ctsrts [CTSRTS]] tty

Runtime configuration control for DapperMime-JTAG

positional arguments:
  tty                Path to DapperMime-JTAG Serprog UART device

optional arguments:
  -h, --help           show this help message and exit
  -v, --verbose        Verbose logging (for this utility)
  --ctsrts [CTSRTS]    Enable or disable CTS/RTS flow control (--ctsrts [true|false])
  --i2ctemp [I2CTEMP]  Control the builtin I2C temperature controller: get (0),
                       disable (-1/0xff) or set/enable (other) the current
                       status and I2C bus address
  --support            Get list of supported/implemented functionality

example:

$ ./dmctl.py /dev/ttyACM1 --ctsrts true

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
  • Parallel ROM flashing support, too, by having the device switch into a separate mode that temporarily disables all other IO protocols
• UART with CTS/RTS flow control
  • Needs configurable stuff as well, as some UART interfaces won't use this.
• Debug interface to send printf stuff directly to USB, instead of having to use the UART interface as a loopback thing.
  • Second UART port for when stdio UART is disabled?
• 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? No. Actually, some parts do, but, laziness.
  • 10-bit I2C address support (Needs poking at the Pico SDK, as it only supports 7-bit ones).
• Host-side script that is an XVC (or hw_server) cable and communicates with the device to perform the JTAG commands, because Vivado no likey OpenOCD.
  • CMSIS-DAP interface can be used directly, see CMSIS_5/CMSIS/DoxyGen/DAP/src/dap_USB_cmds.txt
  • https://github.com/BerkeleyLab/XVC-FTDI-JTAG
  • https://www.eevblog.com/forum/fpga/xilinx-jtag-and-tcf/
  • https://git.eclipse.org/c/tcf/org.eclipse.tcf.git/plain/docs/TCF%20Linux%20Agent%20Prototype.html
  • http://www.eclipse.org/tcf/
  • https://debugmo.de/2012/02/xvcd-the-xilinx-virtual-cable-daemon/
  • https://github.com/Xilinx/XilinxVirtualCable/
  • https://github.com/derekmulcahy/xvcpi
  • OpenOCD as XVC client??
• SUMP logic analyzer?
  • see also this
• Segger RTT?
• Maybe use the ADCs for something?
• General generic manual GPIO mode
• SD/MMC/SDIO (will be a pain)
• AVR programming (USBavr emulation?)
  • AVR ISP is hardly used anymore
  • TPI/UPDI requires 5V levels, Pico doesn't do that :/
  • debugWIRE????
• Renesas E7-{0,1,2} programming thing????
  • Renesas tell us how this works pls
• Maybe steal other features from the Bus Pirate, HydraBus or Glasgow or so
  • 1-wire and 3-wire? Never seen this one in the wild
  • CAN? LIN? If I'd first be able to find a CAN device to test it with, sure