Rising & Falling edge detection

hi,

I'm using EKS-LM3S9D92 board with
sys/bios 6.34.4.22 

and i want to detect rising & falling edge at GPIOC

i  configure peripheral as follow 

ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOC);
ROM_GPIOPinTypeGPIOInput(GPIO_PORTC_BASE, GPIO_PIN_6);
ROM_GPIOIntTypeSet(GPIO_PORTC_BASE, GPIO_PIN_6, GPIO_BOTH_EDGES);
ROM_GPIOPinIntEnable(GPIO_PORTC_BASE, GPIO_PIN_6);
ROM_IntEnable(INT_GPIOC);

and in GPIO HWI

RV= ROM_GPIOIntTypeGet(GPIO_PORTC_BASE, GPIO_PIN_6);
if(RV==GPIO_RISING_EDGE)
{
Semaphore_post(sem);
}
else if(RV==GPIO_FALLING_EDGE)
{

Semaphore_post(sem);

}

but it doesn't detect rising edge ????