Enable external interrupts ARM Cortex-M0+ (STM32G070)

Question

I'm trying to get a fundamental understanding of programming for STM32 microcontrollers. I'm trying to use an external interrupt from a button to toggle the state of an LED, by setting all the appropriate registers (no external libraries/definitions). I can't seem to get the interrupt routine to work, control is never passed to the handler.

Here's what I'm using to set PC-13 (to which there is a button attached as per the Nucleo-G070RB board) as an external interrupt:

RCC_APBENR2  |= 0b1 <<  0; // Enable SYSCFGEN
RCC_IOPENR   |= 0b1 <<  2; // Enable PORTC
EXTI_RTSR1   |= 0b1 << 13; // Enable interrupt on rising edge at EXTI line 13
EXTI_EXTICR4 |= 0x2 <<  8; // Set PC-13 as GPIO pin for interrupt
EXTI_IMR1    |= 0x1 << 13; // Unmask EXTI line 13

NVIC_ISER    |= 0b1 <<  7; // Enable interrupts for EXTI4_15

I'm not sure what I'm missing.

Here's the full code:

#include <stdint.h>
#include <stdio.h>

#define RCC_IOPENR   *((uint32_t volatile *) 0x40021034)
#define RCC_APBENR2  *((uint32_t volatile *) 0x40021040)

#define GPIOA_MODER  *((uint32_t volatile *) 0x50000000)
#define GPIOA_IDR    *((uint32_t volatile *) 0x50000010)
#define GPIOA_ODR    *((uint32_t volatile *) 0x50000014)

#define GPIOC_MODER  *((uint32_t volatile *) 0x50000800)
#define GPIOC_IDR    *((uint32_t volatile *) 0x50000810)
#define GPIOC_ODR    *((uint32_t volatile *) 0x50000814)

#define NVIC_ISER    *((uint32_t volatile *) 0xE000E100)

#define EXTI_RTSR1   *((uint32_t volatile *) 0x40021800)
#define EXTI_EXTICR1 *((uint32_t volatile *) (0x40021800 + 0x060 + 0x4 * 0))
#define EXTI_EXTICR2 *((uint32_t volatile *) (0x40021800 + 0x060 + 0x4 * 1))
#define EXTI_EXTICR3 *((uint32_t volatile *) (0x40021800 + 0x060 + 0x4 * 2))
#define EXTI_EXTICR4 *((uint32_t volatile *) (0x40021800 + 0x060 + 0x4 * 3))
#define EXTI_IMR1    *((uint32_t volatile *) (0x40021800 + 0x080))
#define EXTI_RPR1    *((uint32_t volatile *) (0x40021800 + 0x00C))

void button_init();
extern void initialise_monitor_handles();

uint8_t volatile g_button_pressed = 0;

int main(void) {
    //asm volatile ("cpsie i");
    initialise_monitor_handles();

    //printf("Hello World!\n");

    RCC_IOPENR  |= 0b1 << 0;         // Enable PORTA
    GPIOA_MODER &= ~(0b11 << (2*5)); // Clear MODE bits for 5th pin (PA-5)
    GPIOA_MODER |= 0b1 << (2*5);     // Set MODE bits for 5th pin (PA-5) to 01 (set output)
    GPIOC_MODER &= ~(0b11 << (2*13)); // Clear MODE bits for 13th pin (PC-13) (set input)

    button_init();

    while(1) {
        if (g_button_pressed) {
            GPIOA_ODR ^= 0b1 << 5;
            printf("Button pressed\n");
            g_button_pressed = 0;
        }
    }
}

void button_init() {
    RCC_APBENR2  |= 0b1 <<  0; // Enable SYSCFGEN
    RCC_IOPENR   |= 0b1 <<  2; // Enable PORTC
    EXTI_RTSR1   |= 0b1 << 13; // Enable interrupt on rising edge at EXTI line 13
    EXTI_EXTICR4 |= 0x2 <<  8; // Set PC-13 as GPIO pin for interrupt
    EXTI_IMR1    |= 0x1 << 13; // Unmask EXTI line 13

    NVIC_ISER    |= 0b1 <<  7; // Enable interrupts for EXTI4_15
}

void EXTI4_15_IRQHandler(void) {
    g_button_pressed = 1;
    printf("Button pressed\n");
    EXTI_RPR1 |= 0xFFFF << 0;
}

I'm using the STM32CubeIDE with the default compiler, and and printing via semihosting with OpenOCD.

So, my question is, am I missing a step or doing something wrong?

Answer 1

So, I figured out what my dumb mistake was. I was so focused in trying to understand where I had gone wrong in setting up the external interrupt, I didn't really check if I had set up the button correctly.

I tried to set PC13 as an input:

GPIOC_MODER &= ~(0b11 << (2*13)); // Clear MODE bits for 13th pin (PC-13) (set input)

before I called my button_init() function, which enables the clock for GPIOC via:

RCC_IOPENR   |= 0b1 <<  2; // Enable PORTC

Since GPIOC was not enabled, PC13 was not set as an input either, so there was nothing to detect.

Here's the fixed code: (I also updated it to use the CMSIS stm32 headers, as suggested by P__J__ )

#define STM32G070xx
#include "stm32g0xx.h"

uint8_t volatile g_button_pressed = 0;

void button_init();
//extern void initialise_monitor_handles();

int main(void) {
//  initialise_monitor_handles();

    //printf("Hello World!\n");
    RCC->IOPENR  |= 0b1 << 0;         // Enable PORTA
    GPIOA->MODER &= ~(0b11 << (2*5)); // Clear MODE bits for 5th pin (PA-5)
    GPIOA->MODER |= 0b1 << (2*5);     // Set MODE bits for 5th pin (PA-5) to 01 (set output)

    button_init();

    while(1) {
        if (g_button_pressed) {
            GPIOA->ODR ^= 0b1 << 5;
//          printf("Button pressed! Yay!\n");
            g_button_pressed = 0;
        }
    }
}

void button_init() {
    // RCC->APBENR2    |= (uint32_t) (0b1 <<  0); // Enable SYSCFGEN
    RCC->IOPENR     |= (uint32_t) (0b1 <<  2); // Enable PORTC
    GPIOC->MODER    &= ~(0b11 << (2*13));      // Clear MODE bits for 13th pin (PC-13) (set input)

    EXTI->RTSR1     |= (uint32_t) (0b1 << 13); // Enable interrupt on rising edge at EXTI line 13
    EXTI->EXTICR[3] |= (uint32_t) (0x2 <<  8); // Set PC-13 as GPIO pin for interrupt
    EXTI->IMR1      |= (uint32_t) (0x1 << 13); // Unmask EXTI line 13

    NVIC->ISER[0]   |= (uint32_t) (0b1 <<  7); // Enable interrupts for EXTI4_15
}

void EXTI4_15_IRQHandler(void) {
    g_button_pressed = 1;
//  printf("Button pressed\n");
    EXTI->RPR1 = 0b1 << 13;
}