Flashing Firmware#

The last step is to flash compiled firmware to your microcontroller. RMK supports flashing the firmware via uf2 bootloader or debug probe.

Use uf2 bootloader#

Flashing using uf2 bootloader is easy: set your board to bootloader mode, then a USB drive should appear in your computer. Copy the uf2 firmware to the USB drive, and that's it!

If you're using macOS, an error might appear, you can safely ignore it.

Tips for nRF52840#

For nRF52840, you need to check whether your have a uf2 bootloader flashed to your board. If you can enter bootloader mode, there will be an USB drive shown in your computer. If there's INFO_UF2.TXT in the USB drive, you have it!

The Adafruit_nRF52_Bootloader for nRF52840 has a special MBR section at the beginning of the flash, ensure that the flash origin in memory.x starts with 0x00001000:

If you have a debug probe and don't want to use the bootloader, use the following memory.x config:

Tips for the STM32F411 Blackpill / F401 Bluepill#

For STM32 MCUs the memory.x file us usually created by the embassy-stm32 crate and a memory.x file doesnt have to be created. This will result in a file similar to this: (you can find that in the target directory)

Where the LENGTH value may vary, depending on the chip. This setup works fine for the default stm32-dfu bootloader and the debug probe.

Use tinyuf2 bootloader for stm32#

For some STM32 there is a tinyuf2 bootloader available. Using that you can just drop the finished uf2 file onto the device like it's an USB stick.

Because the bootloader takes up 64K at the beginnning of the first sector, we need to shift the flash address accordingly. To do this first run cargo build --release at least once. get your generated memory.x file out of the target directory:

# pwd in project root
find ./target -name "memory.x"
# example output:
# ./target/thumbv7em-none-eabi/release/build/embassy-stm32-588e747b0f59bbf9/out/memory.x

(The exact path may vary, because of the hash) copy this to your project root:

cp ./target/thumbv7em-none-eabi/release/build/embassy-stm32-dbac6b60f6194464/out/memory.x ./

The file will look something like this:

MEMORY
{
    FLASH : ORIGIN = 0x08000000, LENGTH =  512K /* BANK_1_REGION_1 + BANK_1_REGION_2 + BANK_1_REGION_3 */
    RAM   : ORIGIN = 0x20000000, LENGTH =  128K /* SRAM */
}

For tinyuf2 shift the FLASH region by 64K and adjust the length accordingly:

Then build the firmware using

cargo make uf2 --release

To flash, double tap NRST an the board, the board will go into bootloader mode and appear as a USB flash drive. Drop the *.uf2 files into the drive, the board will then reboot into the firmware.

Use debug probe#

If you have a debug probe like daplink, jlink or stlink(stm32 only), things become much easier: connect it with your board and host, make sure you have installed probe-rs, then just run

cargo run --release

Then the command configured in .cargo/config.toml will be executed. The firmware will be flashed to your microcontroller and run automatically, yay!

Next Steps#

Now you've finished the RMK's user guide. For the next steps, you can checkout features that RMK provides or explore how to configure RMK keyboard: