pico_extexclall_inhibits_wfe.c

#include "hardware/sync.h"
#include "hardware/gpio.h"
#include "hardware/irq.h"
#include "hardware/timer.h"
#include "hardware/uart.h"

#include <stdio.h>

#define ALARM0 0
#define DELAY 1000000

int main() {
    /* if commented out, and "wakes" is an _Atomic, all subsequent WFEs are inhibited */
//    m33_hw->actlr &= ~M33_ACTLR_EXTEXCLALL_BITS;

    /* enable sevonpend so that we don't need a nearly empty isr */
    scb_hw->scr |= M33_SCR_SEVONPEND_BITS;

    /* force clear event register */
    __sev();
    __wfe();

    /* init LED */
    gpio_init(PICO_DEFAULT_LED_PIN);
    gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);

    /* enable uart */
    gpio_set_function(0, UART_FUNCSEL_NUM(uart0, 0));
    gpio_set_function(1, UART_FUNCSEL_NUM(uart0, 1));
    uart_init(uart0, 115200);
    uart_puts(uart0, "\r\nhello\r\n");

    /* enable interrupt for alarm, but leave it disabled in nvic */
    hw_set_bits(&timer_hw->inte, 1u << ALARM0);
    irq_set_enabled(hardware_alarm_get_irq_num(ALARM0), false);

    /* first tick will be one interval from now */
    timer_hw->alarm[ALARM0] = timer_hw->timerawl + DELAY;

    while (1) {
        /* if this is an _Atomic, and EXTEXCLALL is left enabled, all WFEs are inhibited */
        _Atomic unsigned wakes = 0;

        /* wait for alarm to fire, with one wfe per condition check */
        while (!(timer_hw->intr & (1U << ALARM0))) {
            gpio_put(PICO_DEFAULT_LED_PIN, 0);
            __wfe();
            gpio_put(PICO_DEFAULT_LED_PIN, 1);

            wakes++;
        }

        /* acknowledge and clear the interrupt in both timer and nvic */
        hw_clear_bits(&timer_hw->intr, 1U << ALARM0);
        irq_clear(hardware_alarm_get_irq_num(ALARM0));

        /* increment and rearm */
        timer_hw->alarm[ALARM0] += DELAY;

        static char buf[64];
        snprintf(buf, sizeof(buf), "wakes since last alarm: %u\r\n", wakes);
        uart_puts(uart0, buf);
    }
}