The RTC library allows easy access to the LPC1768s interrupt sources on its RTC. There are two different interrupt sources: periodic interrupts, for example every new second, hour, etc, and an alarm, which is called at a specified time.

Hello World!¶

#include "mbed.h"
#include "RTC.h"

DigitalOut led(LED1);

void ledFunction( void )
{
    led = 1;
    RTC::detach(RTC::Second);
}

void displayFunction( void )
{
    time_t seconds = time(NULL);
    printf("%s", ctime(&seconds));
}

void alarmFunction( void )
{
    error("Not most useful alarm function");
}

int main()
{
    set_time(1256729737); // Set time to Wed, 28 Oct 2009 11:35:37

    tm t = RTC::getDefaultTM();
    t.tm_sec = 5;
    t.tm_min = 36;

    RTC::alarm(&alarmFunction, t);
    RTC::attach(&displayFunction, RTC::Second);
    RTC::attach(&ledFunction, RTC::Minute);

    while(1);
}

Periodic interrupts¶

Periodic interrups can be attached by using:

RTC::attach([function], [TimeUnit]);

The TimeUnit specifies which unit should increase for the function to be called. This function is useful if you are making for example a clock: You can simply connect the display update to an RTC interrupt. Of course you can do something similar by using timer objects, but they aren't timed exactly correct, and it is nicer to do it directly on the RTC.

Alarm function¶

The LPC1768's RTC also allows for one alarm to be activated. The alarm goes off the first time there is a compare match on a specified time and the current time. All fields of the normal C tm structure are supported (http://www.cplusplus.com/reference/ctime/tm/), set a field at -1 for it to be ignored. The RTC::getDefaultTM() function helps with that, it returns a tm structure with every field initialized to -1, so don't care.

So if you want to make an alarm that gets called every monday, every 5 minutes and 30 seconds after the hour, you would use:

tm t = RTC::getDefaultTM();
t.tm_sec = 30;     //30 seconds
t.tm_min = 5;      //5 minute
t.tm_wday = 1;     //monday
RTC::alarm([yourFunction], t);

Attaching member functions¶

For compactness of the documentation attaching member functions of objects isn't included. However it works exactly the same as for example attaching one to a Ticker object: http://mbed.org/users/mbed_official/code/mbed/docs/63cdd78b2dc1/classmbed_1_1Ticker.html#af92f41ff11906b1f96fa6bbe0b17aa29

Disclaimer¶

Believe it or not, but I didn't test every possible combination you can make. So I cannot guarantee every alarm setting will work properly.