File content as of revision 4:503239af19b8:

#include "mbed.h"

// Use buttons to select alarm time. Cycle through hours in an incrementing
// fashion using button1, hit select and increment through minutes. Hit
// select one more time to begin the alarm timer.
//
// The Time LEDs will blink in time with the button inputs to show the 
// currently selected alarm time. Once select is hit a second time to begin
// the timer, the LEDs will blink out the configured delay in hours and
// minutes before going into a low power sleep mode.
//
// Once the alarm fires, hitting the select button will turn the alarm off
// until the next time it fires.
//__________________________________________________________________________
// You may also use the RTC (hardware or software through the Time API) to
// set a real world time and set an alarm for a specific timestamp rather
// than on a delay. This would require manually setting the time on each
// reset however, or an internet connection to automatically collect the
// time. See Example <TODO>[HERE] for how to do that.

// Time constants in seconds
#define HOUR   60 * 60
#define MINUTE 60

// Globals
DigitalOut alarm_out(D2, 0);
DigitalOut alarm_led(LED_RED, 1);
DigitalOut hour_led(LED_GREEN, 1);
DigitalOut min_led(LED_BLUE, 1);

InterruptIn inc_time(BUTTON1);
InterruptIn select(BUTTON2);

LowPowerTicker alarm_event;

volatile uint64_t delay        = 0;
volatile uint8_t  hour_count   = 0;
volatile uint8_t  min_count    = 0;
volatile uint8_t  select_state = 0;

// Timer Callbacks
void inc_select(void) {
    if (select_state < 2) {
        select_state++;
    } else {
        // Use select button to disable alarm
        alarm_out = 0;
        alarm_led = 1;
    }
}

void set_time_leds(void) {
    if (select_state == 0) {
        hour_led = !hour_led;
    } else {
        min_led = !min_led;
    }    
}

void inc_delay(void) {
    if (select_state == 0) {
        delay += HOUR;
        hour_count++;
        hour_led = !hour_led;
    } else {
        delay += MINUTE;
        min_count++;
        min_led = !min_led;
    }
}

void trigger_alarm_out(void) {
    alarm_out = 1;
    alarm_led = 0;
}

// Main thread
int main() {
    // Configure interrupt-in pins (button controls)
    select.rise(inc_select);
    inc_time.fall(set_time_leds);
    inc_time.rise(inc_delay);
    
    // Sleep while waiting for user input to set the desired delay
    while (select_state < 2) { wait_ms(10); }
    
    // Once the delay has been input, blink back the configured hours and
    // minutes selected
    for (uint8_t i = 0; i < hour_count * 2; i++) {
        hour_led = !hour_led;
        wait(0.25f);
    }
    
    for (uint8_t i = 0; i < min_count * 2; i++) {
        min_led = !min_led;
        wait(0.25f);
    }

    // Attach the low power ticker with the configured alarm delay
    alarm_event.attach(&trigger_alarm_out, delay);
    
    // Sleep in the main thread
    while (1) { wait(100000); }
}