/*
 * This program generate a sawtooth waveform and a sine wave
 * using the DAC on the Wytec EduBase board.
 *
 * The Wytec EduBase board has a dual channel 12-bit DAC (MCP4922)
 * connected to the Tiva LaunchPad through SSI2.  PORTD 6 is used
 * for slave select.
 */

#include "TM4C123GH6PM.h"
#include <math.h>

void DAC_init(void);
void DAC_write(int value, int channel);

int main(void)
{
    int i = 0;
    float f;

    DAC_init();

    while(1)
    {
        // create a sawtooth waveform
        DAC_write(i++, 0);
        
        // create a sine wave
        f = sinf(0.00314159 * i) * 0x07FF + 0x800;
        DAC_write((int)f, 1);
    }
}

// initialize SSI2 that connects to the DAC
void DAC_init(void)
{
    SYSCTL->RCGCGPIO |= 0x02;   // enable clock to GPIOB  
    SYSCTL->RCGCGPIO |= 0x08;   // enable clock to GPIOD 
    SYSCTL->RCGCSSI |= 0x04;    // enable clock to SSI2

    // PORTB 7, 4 for SSI2
    GPIOB->AFSEL |= 0x90;       // PORTB 7, 4 for SSI2
    GPIOB->PCTL &= ~0xF00F0000; // PORTB 7, 4 for SSI2
    GPIOB->PCTL |= 0x20020000;
    GPIOB->DEN |= 0x90;         // PORTB 7, 4 as digital pins

    // use PD6 for DAC chip select
    GPIOD->DIR |= 0x40;
    GPIOD->DEN |= 0x40;
    GPIOD->AMSEL &= ~0x40;
    GPIOD->DATA |= 0x40;
    
    // initialize SSI2 
    SSI2->CR1 = 0;      // make it master
    SSI2->CC = 0;       // use system clock
    SSI2->CPSR = 16;    // clock prescaler divide by 16 gets 1 MHz clock
    SSI2->CR0 = 0x7;      // clock rate div by 1, phase/polarity 0 0, mode freescale, data size 8
    SSI2->CR1 = 2;      // enable SSI2
}

// write a value to DAC through SSI2
void DAC_write(int value, int channel)
{
    const int BUFFERED = 0x4000;
    const int UNITYGAIN = 0x2000;
    const int NOTSHUTDOWN = 0x1000;
    
    GPIOD->DATA &= ~0x40;       // assert chip select
    value = (value & 0x0FFF) | (channel ? 0x8000 : 0) | BUFFERED | UNITYGAIN | NOTSHUTDOWN;
    SSI2->DR = value >> 8;      // send high byte
    SSI2->DR = value & 0xFF;    // send low byte
    while (SSI2->SR & 0x10) ;   // wait for transmit done
    GPIOD->DATA |= 0x40;        // deassert chip select   
}

// This function is called by the startup assembly
// code to perform system specific initialization tasks.
void SystemInit(void)
{
    // Grant coprocessor access
    // This is required since TM4C123G has
    // a floating point coprocessor
    SCB->CPACR |= 0x00f00000;
}