External Interrupts

The EXTI controller consists of 23 edge detectors, which can be configured individually.

EXTI Lines

0..15	EXTI lines 0..15 correspond to the GPIO pins 0..15
16	PVD interrupt
17	RTC Alarm A & B interrupt
18	USB OTG FS interrupt
19	Ethernet wakeup
20	USB OTG HS interrupt
21	Tamper & time stamp interrupt
22	RTC wakeup interrupt

Configuration Register

SYSCFG_EXTICR1 - External interrupt configuration register 1

SYSCFG_EXTICR2 - External interrupt configuration register 2

SYSCFG_EXTICR3 - External interrupt configuration register 3

SYSCFG_EXTICR4 - External interrupt configuration register 4

Select the source input for EXTI

EXTIx	0000	GPIOA pin x (reset state)
	0001	GPIOB pin x
	…
	1010	GPIOK pin x

EXTI_RTSR / EXTI_FTSR - Rising / falling trigger selection register

TRx	0	Trigger for EXTI line x disabled (reset state)
TRx	1	Trigger for EXTI line x enabled

EXTI_IMR - Interrupt mask register

MRx	0	Interrupt request for EXTI line x masked (reset state)
MRx	1	Interrupt request for EXTI line x unmasked

EXTI_PR - Pending register

PRx*	0	No trigger request occurred
PRx*	1	Selected trigger request occured

* This bit is set when the selected edge event arrives on the external interrupt line x. This bis is cleared by programming it to '1'

Programming Example

Setup Peripheral (e.g. GPIOA Pin 5)

#include "reg_stm32f4xx.h"
 
RCC->AHB1ENR |= (0x1 << 0u);    /* Enable GPIOA clock */
 
/* Configure GPIO pin A.5 as input. */
GPIOA->MODER &= ~(0x3 << 10u);    /* Clear existing mode bits 10 and 11. */
 
GPIOA->PUPDR &= ~(0x3 << 10u);    /* Clear existing pull-up/-down bits 10 and 11. */
GPIOA->PUPDR |= (0x1 << 10u);     /* Set pin 5 to pull-up mode. */

Setup SYSCFG

To choose which GPIO peripheral should trigger EXTI line 5 you have to configure the SYSCFG register.

#include "reg_stm32f4xx.h"
 
SYSCFG->EXTICR2 |= (0u << 4u);  /* Set EXTI5 to GPIOA. */

Setup EXTI

#include "reg_stm32f4xx.h"
 
EXTI->RTSR |= (0x1 << 5u);         /* Trigger on rising edge. */
EXTI->IMR |= (0x1 << 5u);          /* Unmask interrupt line. */

Setup NVIC

#include "reg_stm32f4xx.h"
 
NVIC->ISER0 |= (0x1 << 23u);     /* Enable EXTI5 interrupt. */