Flipper Zero Firmware
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Using FuriHalBus API

Basic info

On system startup, most of the peripheral devices are under reset and not clocked by default. This is done to reduce power consumption and to guarantee that the device will always be in the same state before use. Some crucial peripherals are enabled right away by the system, others must be explicitly enabled by the user code.

NOTE: Here and afterwards the word *"system"* refers to any code belonging to the operating system, hardware drivers or built-in applications.

To ENABLE a peripheral, call furi_hal_bus_enable(). At the time of the call, the peripheral in question MUST be disabled, otherwise a crash will occur to indicate improper use. This means that any given peripheral cannot be enabled twice or more without disabling it first.

To DISABLE a peripheral, call furi_hal_bus_disable(). Likewise, the peripheral in question MUST be enabled, otherwise a crash will occur.

To RESET a peripheral, call furi_hal_bus_reset(). The peripheral in question MUST be enabled, otherwise a crash will occur. This method is used whenever it is necessary to reset all the peripheral's registers to their initial states without disabling it.

Peripherals

Built-in peripherals are divided into three categories:

  • Enabled by the system on startup, never disabled;
  • Enabled and disabled by the system on demand;
  • Enabled and disabled by the user code.

Always-on peripherals

Below is the list of peripherals that are enabled by the system. The user code must NEVER attempt to disable them. If a corresponding API is provided, the user code must employ it in order to access the peripheral.

Table 1 - Peripherals enabled by the system

Peripheral Enabled at
DMA1 furi_hal_dma.c
DMA2
DMAMUX
GPIOA furi_hal_resources.c
GPIOB
GPIOC
GPIOD
GPIOE
GPIOH
PKA furi_hal_bt.c
AES2
HSEM
IPCC
FLASH enabled by hardware

On-demand system peripherals

Below is the list of peripherals that are enabled and disabled by the system. The user code must avoid using them directly, preferring the respective APIs instead.

When not using the API, these peripherals MUST be enabled by the user code and then disabled when not needed anymore.

Table 2 - Peripherals enabled and disabled by the system

Peripheral API header file
RNG furi_hal_random.h
SPI1 furi_hal_spi.h
SPI2
I2C1 furi_hal_i2c.h
I2C3
USART1 furi_hal_serial.h
LPUART1
USB furi_hal_usb.h

On-demand shared peripherals

Below is the list of peripherals that are not enabled by default and MUST be enabled by the user code each time it accesses them.

Note that some of these peripherals may also be used by the system to implement its certain features. The system will take over any given peripheral only when the respective feature is in use.

Table 3 - Peripherals enabled and disabled by user

Peripheral System Purpose
CRC
TSC
ADC
QUADSPI
TIM1 yes subghz, lfrfid, nfc, infrared, etc...
TIM2 yes subghz, infrared, etc...
TIM16 yes speaker
TIM17 yes cc1101_ext
LPTIM1 yes tickless idle timer
LPTIM2 yes pwm
SAI1
LCD

DMA

The DMA1,2 peripherals are a special case in that they have multiple independent channels. Some of the channels may be in use by the system.

Below is the list of DMA channels and their usage by the system.

Table 4 - DMA channels

DMA Channel System Purpose
DMA1 1 yes digital signal
2 yes
3
4 yes pulse reader
5
6 yes USART_Rx
7 yes LPUART_Rx
DMA2 1 yes infrared, lfrfid, subghz,
2 yes
3 yes cc1101_ext
4 yes cc1101_ext
5 yes cc1101_ext
6 yes SPI
7 yes SPI