Posible solution

Labware/Lab12_TuningFork/TuningFork.c

@@ -42,14 +42,34 @@ void DisableInterrupts(void); // Disable interrupts
 void EnableInterrupts(void);  // Enable interrupts
 void WaitForInterrupt(void);  // low power mode
 
+unsigned long flag = 0;
+unsigned long temp = 0;
+unsigned long lastState = 0;
+
 // input from PA3, output from PA2, SysTick interrupts
 void Sound_Init(void){ 
-
+  unsigned long delay;
+  SYSCTL_RCGC2_R |= 0x00000001; // activate port A
+  delay = SYSCTL_RCGC2_R;
+  GPIO_PORTA_AMSEL_R &= ~0x20;      // no analog
+  GPIO_PORTA_PCTL_R &= ~0x000F0000; // regular function
+  GPIO_PORTA_DIR_R |= 0x20;     // make PA5 out
+  GPIO_PORTA_DR8R_R |= 0x20;    // can drive up to 8mA out
+  GPIO_PORTA_AFSEL_R &= ~0x20;  // disable alt funct on PA5
+  GPIO_PORTA_DEN_R |= 0x20;     // enable digital I/O on PA5
+  NVIC_ST_CTRL_R = 0;           // disable SysTick during setup
+  NVIC_ST_RELOAD_R = 39999;     // reload value for 500us (assuming 80MHz)
+  NVIC_ST_CURRENT_R = 0;        // any write to current clears it
+  NVIC_SYS_PRI3_R = NVIC_SYS_PRI3_R&0x00FFFFFF; // priority 0               
+  NVIC_ST_CTRL_R = 0x00000007;  // enable with core clock and interrupts
+  EnableInterrupts();
 }
 
 // called at 880 Hz
 void SysTick_Handler(void){
-
+  if(flag==1)
+		GPIO_PORTA_DATA_R ^= 0x04;
+	else GPIO_PORTA_DATA_R &= ~0x04;
 }
 
 int main(void){// activate grader and set system clock to 80 MHz
@@ -59,5 +79,11 @@ int main(void){// activate grader and set system clock to 80 MHz
   while(1){
     // main program is free to perform other tasks
     // do not use WaitForInterrupt() here, it may cause the TExaS to crash
+    temp = GPIO_PORTA_DATA_R & 0x08;
+		if(temp == 0x08 && lastState == 0x00)
+		{
+			flag ^= 1;
+		}
+		lastState = temp;
   }
 }