EXTI internal peripheral

Revision as of 14:45, 18 March 2021 by Registered User (Merge articles)

1 Peripheral overview[edit]

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). 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>).
  • The 16 GPIO and 4 internal peripheral events 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.

1.1 Features[edit]

Refer to STM32MP15 reference manuals for the complete feature list, and to the software components, introduced below, to see which features are implemented.

1.2 Security support[edit]

The EXTI is a secure peripheral. By default, at reset, all EXTI wake up events are non-secure.

2 Peripheral usage and associated software[edit]

2.1 Boot time[edit]

The EXTI is not used by the boot chain, but is configured during Linux initialization. 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.

2.2 Runtime[edit]

2.2.1 Overview[edit]

The EXTI can be allocated to:

  • the Cortex-A7 non-secure for use in Linux with the interrupts framework

or


2.2.2 Software frameworks[edit]

Internal peripherals software table template

| Core/Interrupts
| EXTI
| 
| Linux interrupt framework
| STM32Cube EXTI driver
|
|-
|}

2.2.3 Peripheral configuration[edit]

The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration can be done alone via the STM32CubeMX tool for all internal peripherals. It can then be manually completed (particularly for external peripherals), according to the information given in the corresponding software framework article.

2.2.4 Peripheral assignment[edit]

Internal peripherals assignment table template

| rowspan="1" | Core/Interrupts
| rowspan="1" | EXTI
| EXTI
|
| 
| 
| Shareable (multiple choices supported)
|-

|}
Info white.png 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