SSI program stall after AFSEL register call.

I am trying to set up the SSI as per the datasheet. I am using the TM4C launchpad and have called for an LED to light after the following two lines, but it never ends up lighting up:

// Alternate function select on PA_2, PA_3, PA_4, PA_5
GPIO_PORTA_AFSEL_R |= (1<<2) | (1<<4) | (2<<5);
GPIO_PORTA_AFSEL_R &= ~(1<<3);

This should be selecting the alternate functions on the IO pins to work as SSI, except for the CS pin (pin PA_3) which I need to manually manipulate. When I run the code on the launchpad the LED does not light up after these two lines. What gives?

-Alex