Tiva C Series TM4C123G LaunchPad Evaluation Board PWM DEMO

Hi,

 i'm trying to use the PWM to change the LEDs (PF1 PF2 PF3) brightness can you help me out?

   SYSCTL->RCGC0 |= (1U << 20);  /* enable clock for PWM */
   SYSCTL->RCGCPWM |= (1U << 1); // for PWM MODULE 1
   SYSCTL->RCGC2 |= (1U << 5);  /* enable clock for GPIOF */
   GPIOF->AFSEL |=(1U << 1 ) | (1U << 2) | (1U << 3); /* Set the GPIO AFSEL bits PF1 PF2 & PF3 */
   GPIOF->PCTL |=(5 << 4 ) | (5 << 8) | (5 << 12); /* Configure the PMCn fields in the GPIOPCTL register 5=PWM */
   SYSCTL->RCC |=(1U << 20 ); /*set the RCC divider for PWM */ 
   SYSCTL->RCC &= ~((0U << 17 ) | (0U << 18 ) | (0U << 19 ));
   //Configure the PWM generator for countdown mode with immediate updates to the parameters.
   PWM1->_2_CTL |= (0x0000 << 0);
   PWM1->_3_GENA |=(0x8C << 0);
   PWM1->_2_GENB |=(0x80C << 0);  
   PWM1->_3_GENB |=(0x80C << 0);
   //Set the period. For a 50Hz frequency
   PWM1->_2_LOAD |=(0x3E7F << 0);
   PWM1->_3_LOAD |=(0x3E7F << 0);
   //Set the pulse width pin for a 25% duty cycle
   PWM1->_2_CMPB |=(0x12B <<0);
   PWM1->_3_CMPA |=(0x12B <<0);
   PWM1->_3_CMPB |=(0x12B <<0);
   //Start the timers in PWM generators.
   PWM1->_2_CTL |=(1U << 0 );
   PWM1->_3_CTL |=(1U << 0 );
   //Enable PWM outputs.
   PWM1->ENABLE |=(0xE << 4);
   while(1){}