basic_bootloader

basic_bootloader

Description

The application provides a basic bootloader that can be combined with other applications to perform a specific functionality at boot time.

If you want to learn more about the purpose of a bootloader, we recommend reading this great blog post.

basic_bootloader performs one of two functionalities based on the GNSE button:

1. If the button is not pressed -> boots the user flashed application
2. If the button is pressed long enough -> boots the ST internal bootloader

Configuration

basic_bootloader key configurations:

Memory Map

The internal flash (ROM) memory map can be configured to accommodate a bootloader and an application by adjusting the parameters defined in memory_map.ld.

BOOTROM  (rx)  : ORIGIN = 0x08000000, LENGTH = 0x00000B000   /* Flash memory dedicated to bootloader */
APPROM   (rx)  : ORIGIN = 0x0800B000, LENGTH = 0x000035000   /* Flash memory dedicated to application */

App activity

The application behavior can be adjusted by modifying conf/app_conf.h.

• GNSE_TINY_TRACER_ENABLE enables UART (115200/8-N-1) logging of application activity

#define GNSE_TINY_TRACER_ENABLE 1

Please note that it is considered as a best practice to disable logging when building bootloaders to reduce the binary size.

Setup

To build a basic_bootloader that can be combined with another application in the same memory, you need to use a linker script that supports the new memory map.

Building with CMake

If you are building using CMake, then update CMakeLists.txt LINKER_SCRIPT flag to bootloader.ld when compiling a basic_bootloader binary.

set(LINKER_SCRIPT ${MCU_DIR}/bootloader.ld)

Also, make sure to update LINKER_SCRIPT flag to app.ld when compiling an application binary that will be combined with the bootloader binary.

set(LINKER_SCRIPT ${MCU_DIR}/app.ld)

Building with STM32CubeIDE

If you are building using STM32CubeIDE, then there is no need to change the linker script when building a basic_bootloader binary as can be seen below.

But, make sure to change the application linker script from ../../../target/stm32wl55xx_flash.ld to ../../../target/app.ld.

Combining applications

You can combine two binaries such as the basic_bootloader and basic_lorawan by using the bootloader_app_merge python script.

For example:

python bootloader_app_merge.py \
-b ./build/debug/app/basic_bootloader/main.bin \
-a ./build/debug/app/basic_lorawan/main.bin \
-s 1 \
-d 0xB000 \
-c 0xB008 \
-o ./build/debug/app/basic_lorawan/boot_basic_lorawan.bin

Observation

The device boots and turns on the red LED.

If the button is not pressed, the red LED will stay on for a small period and the device will boot the user-flashed application.

If the button is pressed for long enough, it will turn on the blue LED and turn off the red LED, indicating a successful input and it will continue to boot the ST internal bootloader.