flipperzero-firmware/wiki/fw/Firmware.md

Overview of Flipper firmware architecture:

HAL

We use STM32 HAL/LL. Description available here: dm00105879.pdf

Flipper HAL

Some flipper-specific implementation of gpio/HAL:

• Init gpio pin: app_gpio_init
• Fast write gpio (inline): app_gpio_write
• Fast read gpio (inline): app_gpio_read
• Microsecond delay delay_us
• Set PWM on timer's pin: pwm_set

Files location: /app/app_hal.[ch]

OS

We use FreeRTOS 10.0.1 for sheduling. Documentation available on freertos.org.

Files location for L476 version: /target_prod/Middlewares/Third_Party/FreeRTOS

Timers map

Platform code

CMSIS, Freertos and HAL files are generated by CubeMX. You can find platform code for L476 version in target_prod folder:

• Drivers/STM32L4xx_HAL_Driver – hardware abstraction layer
• Drivers/CMSIS — ARM specific code
• Inc Src — CubeMX generated headers & code
• Middlewares/Third_Party/FreeRTOS/Source — freeRTOS
• deploy.sh — flash firmware to device
• STM32L476RGTx_FLASH.ld — linker script
• startup_stm32l476xx.s — board startup/initialization assembler code
• flipperzero_l476.ioc — CubeMX project file

You can regenerate platform code:

1. Download CubeMX from st.com
2. Open *.ioc file
3. Click generate code
4. After regenerating, look at git status, regenerating may broke some files.

Arduino compatibility

There are some arduino-style defines (digitalWrite, delay, etc.). Include Arduino.h from /app/Arduino.h

Debug print

You can use pintf to write any message to debug UART. UART specify in Makefile as -DDEBUG_UART=<>.

Implementation of write method located at /app/write.c

Flipper Universal Registry Implementation (FURI)

FURI is used to:

• application control (start, exit, switch between active)
• data exchange between application (create/open channel, subscribe and push messages or read/write values)
• non-volatile data storage for application (create/open value and read/write)

Read more at FURI page

FS

File system is used to volaile storage some files (config, application data, etc.). There are some folders mounted to different volumes:

• /usr for store static data like assets, menu items. Build system add files to usr while building. It can be useful for exchange some static data between application. For example, your app can add link to itself to Plugins menu items file, user will see your app and can call it from this menu.
• Specially /usr/etc-default folder contains default configs for apps. Bootloader has factory default options to reset applications config. Also when new app is bootstapping, system copy files from default config folder to /etc.
• /etc for store configs of application. This volume not overwrite during flashing.
• /var for store some application data (saved keys, application database, logs). This volume also not overwrite during flashing.
• /media/* mounted if SD card is inserted.

Flipper applications

Each flipper functionality except OS/HAL/FURI doing by Flipper application. Some application are called at startup, the rest are called by the user (for example, from menu).

List of Flipper applications

For exchange data between application each app expose own record in FURI. You can subscribe on/read record to get data from application and write to record to send data to application.

List of FURI records

Flipper libraries

Unlike applications that run after startup, libraries are a collection of constants, types, or functions that the user can call from within the application.

List of Flipper libraries

Bootloader

After start, bootloader run first. It can:

1. Runs main firmware
2. Reflashes firmware from temporary area after updating from usb/bluetooth
3. Restores factory default firmware for protected flash area
4. Restores application settings to default by clearing /etc volume

Building

Build in docker container (main way)

1. Install docker compose
2. After startup you should run docker-compose up -d to run the container.
3. Then you can run docker-compose exec dev make to build application.

If Dockerfile is changed you should run docker-compose down and docker-compose build for rebuild the image.

Build in IDE

• Arduino IDE (in progress)
• PlatformIO (in progress)