Setting the Hibernation RTC clock

Thanks for the reply Amit, especially point 3, it was a bit confusing for me when i read it on the data sheet. With your clarification and a bit of trail and error I was able to produce the following code that is meant to simply generate the sought after, 1Hz interrupt:

#include "inc/hw_hibernate.h"
#include "driverlib/sysctl.h"
#include "driverlib/interrupt.h"
#include "driverlib/debug.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/hibernate.h"

//
// Handler for hibernate interrupts.
//
void HibernateISRHandler(void)
{
	uint32_t ui32Status;

	// Get the interrupt status and clear any pending interrupts.
	ui32Status = HibernateIntStatus(true);
	HibernateIntClear(ui32Status);

	// Process the RTC match 0 interrupt.
	if(ui32Status & HIBERNATE_INT_RTC_MATCH_0)
	{
		// update match value
		uint32_t ui32RTCMatch;
		ui32RTCMatch = HibernateRTCMatchGet(0);
		HibernateRTCMatchSet(0,ui32RTCMatch + 1);	// a second in the future

//		HibernateRTCSet(0);							// reset RTC count

		// toggle gpio value
		if(GPIOPinRead(GPIO_PORTF_BASE, GPIO_PIN_3))
		{
			GPIOPinWrite(GPIO_PORTF_BASE,GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3,0x00);
		}
		else
		{
			GPIOPinWrite(GPIO_PORTF_BASE,GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3,0x08);
		}

	}

}

//
// main function
//
int main(void)
                              {
	// run system clock at 40-MHz
	SysCtlClockSet(SYSCTL_SYSDIV_5 | SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ |
			       SYSCTL_OSC_MAIN);

	// GPIO Config RGB: 2=red=pin1, 4=blue=pin2 and 8=green=pin3
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
	GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3);
	GPIOPinWrite(GPIO_PORTF_BASE,GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3, 0x08);

	// Hibernation Module config
	SysCtlPeripheralEnable(SYSCTL_PERIPH_HIBERNATE);
	HibernateEnableExpClk(0);		// set HIBCTL.CLK32EN, input irelevant
	while(!(HWREG(HIB_RIS) & HIB_RIS_WC)) {}	// wait for clk stability
	HibernateClockConfig(HIBERNATE_OSC_LOWDRIVE);
	SysCtlDelay(64000000);

	// Hib RTC Config
	HibernateRTCEnable();							// start RTC count
	HibernateRTCSet(0);								// load RTC value
	HibernateRTCMatchSet(0,5);						// set match value
	HibernateIntEnable(HIBERNATE_INT_RTC_MATCH_0);	// En RTC match interrupt

	// MCU intrrupt set up
	IntEnable(INT_HIBERNATE_TM4C123);
	IntMasterEnable();

	// signal for me
	GPIOPinWrite(GPIO_PORTF_BASE,GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3, 0x00);

	// catch loop
	while(1)
	{
		if(HibernateRTCGet() > HibernateRTCMatchGet(0))
		{
			_nop();
		}
	}

}

The above code does generate a 1Hz interrupt as expected but after about 65 seconds the interrupt is no longer generated. As if the RTC count somehow surpassed the match value (hibernation register inspection revealed this to be the case) but how is this so? The processor is running at 40-MHz, it has a whole second before the RTC count value is increased and the Hibernation ISR is pretty short.I inspected the

I inspected the driverlib/hibernation.c source code and it uses a static function called _HibernateWriteComplete() which polls the WRC bit in the HIBCTL to make sure hibernation register writes are completed before proceeding but in theory, the hibernation module registers running at 32.769-kHz meaning that only a single cycle (1/32768 of a second) is necessary to complete the write. In my ISR I only make 2 writes to Hibernation module registers which does not add up to the whole second I have before the RTC count in increased. I know there are additional timing overhead sources I'm not considering like: the ISR service time, and the function calls made inside the ISR itself but even if considered these overheads would not explain why does the RTC count value Increase beyond the RTC match value. maybe its something I'm missing.

I also tried simply resetting the RTC count to zero in the ISR to see if it improved the problem. The ISR kept firing well after five minutes but not at a 1Hz, it was well over.

Thank you Amit, I just tried the modification to the code you suggested and it's been generating the interrupt consistently. Thank you, for your time, your patients and for being so kind.