Sound.c

// Sound.c
// Runs on LM4F120 or TM4C123, 
// edX lab 13 
// Use the SysTick timer to request interrupts at a particular period.
// Daniel Valvano, Jonathan Valvano
// December 29, 2014
// This routine calls the 4-bit DAC

#include "Sound.h"
#include "DAC.h"
#include "..//tm4c123gh6pm.h"
static unsigned short enabled, index; 
const unsigned char SineWave32[32] = {8,9,11,12,13,14,14,15,15,15,14,14,13,12,11,9,8,7,5,4,3,2,2,1,1,1,2,2,3,4,5,7};
// **************Sound_Init*********************
// Initialize Systick periodic interrupts
// Also calls DAC_Init() to initialize DAC
// Input: none
// Output: none
void Sound_Init(void){
	  NVIC_ST_CTRL_R = 0;           // disable SysTick during setup
  NVIC_SYS_PRI3_R = NVIC_SYS_PRI3_R&0x00FFFFFF; // priority 0               
  NVIC_ST_CTRL_R = 0x00000007;  // enable with core clock and interrupts
	DAC_Init();
	index=0;
}

// **************Sound_Tone*********************
// Change Systick periodic interrupts to start sound output
// Input: interrupt period
//           Units of period are 12.5ns
//           Maximum is 2^24-1
//           Minimum is determined by length of ISR
// Output: none
void Sound_Tone(unsigned long period){
// this routine sets the RELOAD and starts SysTick
  NVIC_ST_RELOAD_R = period-1;    // reload value for 500us (assuming 80MHz)
	enabled=1;
}


// **************Sound_Off*********************
// stop outputing to DAC
// Output: none
void Sound_Off(void){
 // this routine stops the sound output
	DAC_Out(0x00); //Turns off the output
	enabled=0;
}


// Interrupt service routine
// Executed every 12.5ns*(period)
void SysTick_Handler(void){

index = (index+1)&0x1F;
  if (enabled != 0) {   
		DAC_Out(SineWave32[index]);
	}
}