TinyUF2 is an open source cross-platform UF2 bootloader based on the TinyUSB library.

Checkout the code and sync submodules:

$ git clone https://github.com/arturo182/tinyuf2.git
$ cd tinyuf2
$ git submodule update --init --recursive

Specify the board you want to build for:

$ make BOARD=mimxrt1010_evk

The filesystem is structured as follows;

        tinyuf2
           |
           +----hw                    Hardware specific files
           |    |
           |    +---bsp                 Board specific files
           |    |
           |    +---chip                Chip specific (multiple boards)
           |
           +----lib                   External supporting libraries
           |
           +----src                   tinyUF2 specific code

A board is selected by means of the BOARD option on the makefile command line. This references a particular hw/bsp/<BOARD> directory which then links to a specific chip and variant in the hw/chip/ directories. A new board is added under /hw/bsp/<BOARD>. It may optionally need a new chip or variant under the hw/chip directories or, more normally, it might need new pin options in hw/chip/<FAMILY>/<GROUP>/pinning_options.h.

You can add a new board by copying an existing one that is closest to it in the hw/ directory with something like cp -a hw/bsp/mimxrt1010_evk hw/bsp/newboard. Edit hw/bsp/newboard/board.mk to reference the appropriate hw/chip directory and the board_config.h file to adjust settings for the new board.

In general entries in hw/bsp/newboard/board.mk should reference existing pinning definitions in the relavent hw/chip directory rather than being created afresh.

In general non-standard options are frowned upon because it changes the user experience of tinyUF2. However, on occasion these may be needed for specific reasons. The supported options are specified in hw/bsp/<BOARD>/board_config.h for a specific board. Not defining any of these options means sensible defaults will be applied;

• USB_VID: Vendor ID for the board. Default is 0x239A, courtesy of Adafruit Industries.

• USB_PID: PID for the board. Default is 0x0058 which is specifically defined as a generic tinyUF2 boot device. Do not select something else unless you've been allocated a new number by Adafruit.

• VOLUME_LABEL: Volume Label for the tinyUF2 drive. Default is UF2BOOT.

• BOARD_TAP_WAIT: How long to wait for double-tap entry into bootloader before performing regular boot. Default is 500mS.

• BOARD_BLINK_INTERVAL: Blinking interval while in tinyUF2. Default is 500uS on/off.

• BOARD_LED_ON_UF2_START: Should the LED be on or off at UF2 boot? Default is off.