/*
 * Display number 2014 on the seven-segment LED for TI Tiva LaunchPad
 * with Wytec EduBase.
 * The four digit seven segment LED is driven by two shift registers,
 * one to control the anodes (segments) and the other the common cathods
 * (digit select).  The shift registers are daisy-chained to SSI2
 * of the Tiva LaunchPad.
 * Each digit is enabled for 4 ms.  With four digits, the cycle time is
 * 4 ms * 4 = 16 ms that translates to 62.5 Hz.
 */

#include "TM4C123GH6PM.h"

void delayMs(int n);
void delayUs(int n);
void sevenseg_init(void);
void SSI2_write(unsigned char data);

int main(void)
{
    // initialize SSI2 that connects to the shift registers
    sevenseg_init();
    
    while(1)
    {
        SSI2_write(0x5B);       // write pattern 2 to the seven segments
        SSI2_write(~(1 << 3));  // select digit 3
        delayMs(4);

        SSI2_write(0x3F);       // write pattern 0 to the seven segments
        SSI2_write(~(1 << 2));  // select digit 2
        delayMs(4);
        
        SSI2_write(0x06);       // write pattern 1 to the seven segments
        SSI2_write(~(1 << 1));  // select digit 1
        delayMs(4);
        
        SSI2_write(0x66);       // write pattern 4 to the seven segments
        SSI2_write(~(1 << 0));  // select digit 0
        delayMs(4);
    }
}

// enable SSI2 and associated GPIO pins
void sevenseg_init(void)
{
    SYSCTL->RCGCGPIO |= 0x02;   // enable clock to GPIOB
    SYSCTL->RCGCGPIO |= 0x04;   // enable clock to GPIOC
    SYSCTL->RCGCSSI |= 0x04;    // enable clock to SSI2

    // PORTB 7, 4 for SSI2 TX and SCLK
    GPIOB->AMSEL &= ~0x90;      // turn off analog of PORTB 7, 4 
    GPIOB->AFSEL |= 0x90;       // PORTB 7, 4 for alternate function
    GPIOB->PCTL &= ~0xF00F0000; // clear functions for PORTB 7, 4
    GPIOB->PCTL |= 0x20020000;  // PORTB 7, 4 for SSI2 function
    GPIOB->DEN |= 0x90;         // PORTB 7, 4 as digital pins

    // PORTC 7 for SSI2 slave select
    GPIOC->AMSEL &= ~0x80;      // disable analog of PORTC 7
    GPIOC->DATA |= 0x80;        // set PORTC 7 idle high
    GPIOC->DIR |= 0x80;         // set PORTC 7 as output for SS 
    GPIOC->DEN |= 0x80;         // set PORTC 7 as digital pin     

    SSI2->CR1 = 0;              // turn off SSI2 during configuration
    SSI2->CC = 0;               // use system clock
    SSI2->CPSR = 16;            // clock prescaler divide by 16 gets 1 MHz clock
    SSI2->CR0 = 0x0007;         // clock rate div by 1, phase/polarity 0 0, mode freescale, data size 8
    SSI2->CR1 = 2;              // enable SSI2 as master
}

// This function enables slave select, writes one byte to SSI2,
// wait for transmit complete and deassert slave select.
void SSI2_write(unsigned char data)
{
    GPIOC->DATA &= ~0x80;       // assert slave select
    SSI2->DR = data;            // write data
    while (SSI2->SR & 0x10) {}  // wait for transmit done
    GPIOC->DATA |= 0x80;        // deassert slave select
}

// delay n milliseconds (16 MHz CPU clock)
void delayMs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 3180; j++)
            {}  // do nothing for 1 ms
}

// delay n microseconds (16 MHz CPU clock)
void delayUs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 3; j++)
            {}  // do nothing for 1 us
}

// 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;
}