diff --git a/embassy-boot-nrf/README.md b/embassy-boot-nrf/README.md index f0d87e18c..b77cf80bd 100644 --- a/embassy-boot-nrf/README.md +++ b/embassy-boot-nrf/README.md @@ -6,6 +6,25 @@ An adaptation of `embassy-boot` for nRF. ## Features -* Load applications with or without the softdevice. -* Configure bootloader partitions based on linker script. -* Using watchdog timer to detect application failure. +- Load applications with or without the softdevice. +- Configure bootloader partitions based on linker script. +- Using watchdog timer to detect application failure. + +## Working with a SoftDevice + +When a SoftDevice is present, it handles starting the bootloader and the application as needed. + +The SoftDevice architecture supports the bootloader via a configurable base address, referred to as `BOOTLOADERADDR`, in the application flash region. This address can be specified either: + +1. At the `MBR_BOOTLOADER_ADDR` location in flash memory (defined in `nrf_mbr.h`), or +2. In the `UICR.NRFFW[0]` register. + +The `UICR.NRFFW[0]` register is used only if `MBR_BOOTLOADER_ADDR` has its default value of `0xFFFFFFFF`. This bootloader relies on the latter approach. + +In the `memory.x` linker script, there is a section `.uicr_bootloader_start_address` (origin `0x10001014`, length `0x4`) that stores the `BOOTLOADERADDR` value. +Ensure that `__bootloader_start` is set to the origin address of the bootloader partition. + +When a bootloader is present, the SoftDevice forwards interrupts to it and executes the bootloader reset handler, defined in the bootloader's vector table at `BOOTLOADERADDR`. + +Once the bootloader loads the application, the SoftDevice initiates the Application Reset Handler, defined in the application’s vector table at APP_CODE_BASE hardcoded in the SoftDevice. +The active partition's origin **must** match the `APP_CODE_BASE` value hardcoded within the SoftDevice. This value can be found in the release notes for each SoftDevice version.