#include <stdio.h>        //provides printf function
#include "pico/stdlib.h"  //provides standard library for the pico
#include "hardware/timer.h" //provides timer registers
#include "hardware/irq.h"   //provides irq registers

// 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;
}

#if PICO_TIME_DEFAULT_ALARM_POOL_DISABLED
#error boom
#endif

// Forward declaration
static void alarm_in_us(uint32_t delay_us);

// Use alarm 0
#define ALARM_NUM 0
#define ALARM_IRQ TIMER_IRQ_0

#define ALARM_SECOND 1000000L

uint64_t randomWait() {
  // Wait between 1 and 4 seconds
  return ALARM_SECOND + ((rand() * UINT32_MAX) % (ALARM_SECOND*3));
}

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

    uint64_t sleepy=randomWait();
    uint64_t now=time_us_64();

    // Assume alarm 0 has fired
    printf("%9llu ms Timer 0 fired!, will fire again in %0.3f\n", now/1000,sleepy/(float)ALARM_SECOND);

    alarm_in_us(sleepy);
}

// Set alarm
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("Hello Timer! (Low Level)\n");

    alarm_in_us(ALARM_SECOND << 1); //2 second alarm

    while (1) {
        sleep_ms(1000);
    }
}