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Free-DAP

This is a free and open implementation of the CMSIS-DAP debugger firmware.

Both SWD and JTAG protocols are supported. However JTAG was not well tested due to lack of good targets. If you have any issues with it - let me know and I'll try to help.

Platform requirements

To create a CMSIS-DAP compliant debugger, your platform must:

  • Implement USB HID (and raw bulk for CMSIS-DAP v2) device able to receive and send arbitrary payloads
  • Provide configuration file dap_config.h with definitions for hardware-dependent calls
  • Call dap_init() at the initialization time
  • Call dap_process_request() for every received request and send the response back

CMSIS-DAP version support

Free-DAP library itself is protocol agnostic and implementation of the specific version of the CMSIS-DAP protocol (v1 or v2) is up to the individual platforms.

Currently RP2040 and SAM D11 implementaitons were updated to support CMSIS-DAP v2. Other platforms would be updated if requested or needed by me.

Configuration

For complete list of settings see one of the existing configuration file, they are pretty obvious.

To configure clock frequency you need to specify two parameters:

  • DAP_CONFIG_DELAY_CONSTANT - clock timing constant. This constant can be determined by calling dap_clock_test() with varying parameter value and measuring the frequency on the SWCLK pin. Delay constant value is the value of the parameter at which output frequency equals to 1 kHz.
  • DAP_CONFIG_FAST_CLOCK - threshold for switching to fast clock routines. This value defines the frequency, at which more optimal pin manipulation functions are used. This is the frequency produced by dap_clock_test(1) on the SWCLK pin. You can also measure maximum achievable frequency on your platform by calling dap_clock_test(0).

Your configuration file will need to define the following pin manipulation functions:

  • DAP_CONFIG_SWCLK_TCK_write()
  • DAP_CONFIG_SWDIO_TMS_write()
  • DAP_CONFIG_TDO_write()
  • DAP_CONFIG_nTRST_write()
  • DAP_CONFIG_nRESET_write()
  • DAP_CONFIG_SWCLK_TCK_read()
  • DAP_CONFIG_SWDIO_TMS_read()
  • DAP_CONFIG_TDI_read()
  • DAP_CONFIG_TDO_read()
  • DAP_CONFIG_nTRST_read()
  • DAP_CONFIG_nRESET_read()
  • DAP_CONFIG_SWCLK_TCK_set()
  • DAP_CONFIG_SWCLK_TCK_clr()
  • DAP_CONFIG_SWDIO_TMS_in()
  • DAP_CONFIG_SWDIO_TMS_out()

Note that all pin manipulation functions are required even if one of the interfaces (JTAG or SWD) is not enabled.

Additionally configuration file must provide basic initialization and control functions:

  • DAP_CONFIG_SETUP()
  • DAP_CONFIG_DISCONNECT()
  • DAP_CONFIG_CONNECT_SWD()
  • DAP_CONFIG_CONNECT_JTAG()
  • DAP_CONFIG_LED()
  • DAP_CONFIG_DELAY()

Tools

A complete RP2040 build requres bin2uf2 utility to generate UF2 file suitable for the RP2040 MSC bootloader. This utility can be downloded here.

Binaries

Generally there are no pre-built binaries due to effort required to maintain them and low potential benefit because of custom hardware requirement.

For RP2040 and Raspberry Pi Pico board specifically there is a binary, since it is a standard and a widely available board that has a nonvolatile bootloader.

The UF2 file is located here. Simply boot into a BootROM MSC mode and copy that file to the drive.

I will try to do my best to keep this binary in sync with the code updates, but it is a manual process, so I may forget. Let me know if you have any issues.

The pins used are as follows:

GPIO Function
11 SWCLK/TCK
12 SWDIO/TMS
13 TDI
14 TDO
15 nRESET
0 VCP TX
1 VCP RX
2 VCP Status
25 (LED) DAP Status

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Free and open implementation of the CMSIS-DAP debugger firmware

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