timer_lowlevel.c

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/timer.h"
#include "hardware/irq.h"

/// \tag::get_time[]
// Simplest form of getting 64 bit time from the timer.
// It isn't safe when called from 2 cores because of the latching
// so isn't implemented this way in the sdk
static uint64_t get_time(void) {
    // Reading low latches the high value
    uint32_t lo = timer_hw->timelr;
    uint32_t hi = timer_hw->timehr;
    return ((uint64_t) hi << 32u) | lo;
}
/// \end::get_time[]

/// \tag::alarm_standalone[]
// Use alarm 0
#define ALARM_NUM 0
#define ALARM_IRQ TIMER_IRQ_0

// Alarm interrupt handler
static volatile bool alarm_fired;

static void alarm_irq(void) {
    // Clear the alarm irq
    hw_clear_bits(&timer_hw->intr, 1u << ALARM_NUM);

    // Assume alarm 0 has fired
    printf("Alarm IRQ fired\n");
    alarm_fired = true;
}

static void alarm_in_us(uint32_t delay_us) {
    // Enable the interrupt for our alarm (the timer outputs 4 alarm irqs)
    hw_set_bits(&timer_hw->inte, 1u << ALARM_NUM);
    // Set irq handler for alarm irq
    irq_set_exclusive_handler(ALARM_IRQ, alarm_irq);
    // Enable the alarm irq
    irq_set_enabled(ALARM_IRQ, true);
    // Enable interrupt in block and at processor

    // Alarm is only 32 bits so if trying to delay more
    // than that need to be careful and keep track of the upper
    // bits
    uint64_t target = timer_hw->timerawl + delay_us;

    // Write the lower 32 bits of the target time to the alarm which
    // will arm it
    timer_hw->alarm[ALARM_NUM] = (uint32_t) target;
}

int main() {
    stdio_init_all();
    printf("Timer lowlevel!\n");

    // Set alarm every 2 seconds
    while (1) {
        alarm_fired = false;
        alarm_in_us(1000000 * 2);
        // Wait for alarm to fire
        while (!alarm_fired);
    }
}

/// \end::alarm_standalone[]