EXTI internal peripheral

Applicable for

1. Article purpose[edit | edit source]

The purpose of this article is to:

briefly introduce the EXTI peripheral and its main features,
indicate the peripheral instances assignment at boot time and their assignment at runtime (including whether instances can be allocated to secure contexts),
list the software frameworks and drivers managing the peripheral,
explain how to configure the peripheral.

2. Peripheral overview[edit | edit source]

The EXTI peripheral is used to get an interrupt when a GPIO is toggling. It can also wake up the system from Stop low power mode, by means of the PWR internal peripheral when a wake up event occurs, before (eventualy - see the note below) propagating an interrupt to the client processor (Cortex-A7 GIC or Cortex-M4 NVIC in case of STM32MP15). The wake up events can be internal (from other IPs clocked by the LSE, LSI or HSI from RCC), or external (from GPIO).

Notice that:

Up to 16 GPIO pins can be configured as external interrupts: for each index between 0 and 15, one EXTI can be selected among all banks (EXTI<index> = GPIO<one_bank><index>).
On STM32MP13x lines : The 16 GPIO and one internal peripheral events ( AVD/PVD), can generate interrupts connected to the GIC. All the other internal peripheral events can wake up the system, but the EXTI does not generate any interrupt to the GIC; in such cases, another peripheral interrupt has to be used as a trigger via the GIC.
On STM32MP15x lines : The 16 GPIO and 5 internal peripheral events (AVD/PVD, CPU1 SEV, CPU2 SEV, WWDG1 reset, CPU2 SYSRESETREQ) can generate interrupts connected to the GIC and NVIC. All the other internal peripheral events can wake up the system, but the EXTI does not generate any interrupt to the GIC or NVIC for them; in such cases, another peripheral interrupt has to be used as a trigger via the GIC or NVIC.
By default, at reset, all EXTI wake up events are non-secure.

Refer to the STM32 MPU reference manuals for the complete list of features, and to the software frameworks and drivers, introduced below, to see which features are implemented.

3. Peripheral usage[edit | edit source]

This chapter is applicable in the scope of the OpenSTLinux BSP running on the Arm^® Cortex^®-A processor(s), and the STM32CubeMPU Package running on the Arm^® Cortex^®-M processor.

3.1. Boot time assignment[edit | edit source]

The EXTI peripheral is not used at boot time, but is configured during Linux initialization.

3.1.1. On STM32MP15x lines [edit | edit source]

Since wake-up event configuration is done via register bit-field reads and writes, concurrent accesses from Linux and the coprocessor are not possible at boot time:

Linux configures all EXTI events during their respective consumer driver probing
The coprocessor uses the resource management mechanisms to request and configure the EXTI events it needs.

3.2. Runtime assignment[edit | edit source]

3.2.1. On STM32MP13x lines [edit | edit source]

Click on the right to expand the legend...

STM32MP13 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by STM32 MPU Embedded Software:

☐ means that the peripheral can be assigned (☑) to the given runtime context.
⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
✓ is used for system peripherals that cannot be unchecked because they are statically connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP13 reference manuals.

Domain	Peripheral	Runtime allocation			Comment
Domain	Peripheral	Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Comment
Core/Interrupts	EXTI	EXTI	✓	✓

3.2.2. On STM32MP15x lines [edit | edit source]

Click on the right to expand the legend...

STM32MP15 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by STM32 MPU Embedded Software:

☐ means that the peripheral can be assigned (☑) to the given runtime context.
⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
✓ is used for system peripherals that cannot be unchecked because they are statically connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possiblities might be described in STM32MP15 reference manuals.

Domain	Peripheral	Runtime allocation				Comment
Domain	Peripheral	Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Cortex-M4 (STM32Cube)	Comment
Core/Interrupts	EXTI	EXTI	⬚	✓	✓	Shared

Information

The EXTI peripheral is not listed in STM32CubeMX peripherals list because its configuration is partly embedded in the Device tree (for all internal EXTI sources, coming from peripherals with wake up capabilities) and completed with the GPIO configuration that comes from STM32CubeMX pinout view

The OP-TEE EXTI driver is not activated and not used by OpenSTLinux on STM32MP15x lines .

4. Software frameworks and drivers[edit | edit source]

Below are listed the software frameworks and drivers managing the EXTI peripheral for the embedded software components listed in the above tables.

Linux^®: interrupts framework
OP-TEE: OP-TEE EXTI driver
STM32Cube: HAL EXTI driver

5. How to assign and configure the peripheral[edit | edit source]

The peripheral assignment can be done via the STM32CubeMX graphical tool (and manually completed if needed).
This tool also helps to configure the peripheral:

partial device trees (pin control and clock tree) generation for the OpenSTLinux software components,
HAL initialization code generation for the STM32CubeMPU Package.

The configuration is applied by the firmware running in the context in which the peripheral is assigned.

See also additional information in the Interrupt device tree configuration article for Linux^®.