/* Initialize LCD controller and flash "HELLO" on the LCD.
 *
 * The connections between the LCD controller of EduPad 
 * board and the Tiva LaunchPad are
 * 
 * PA2-PA5 for LCD D4-D7, respectively. 
 * PE0 for LCD R/S
 * PC6 for LCD EN
 *
 * For simplicity, all delay below 1 ms uses 1 ms.
 *
 * Built and tested with Keil MDK-ARM v5.24a and TM4C_DFP v1.1.0
 */

#include "TM4C123GH6PM.h"

#define RS 1    // BIT0 mask for reg select
#define EN 2    // BIT1 mask for E

void delayMs(int n);
void LCD_nibble_write(char data, unsigned char control);
void LCD_command(unsigned char command);
void LCD_data(char data);
void LCD_init(void);
void PORTS_init(void);

int main(void) {
    // initialize LCD controller
    LCD_init();

    while(1) {
        // Write "HELLO" on LCD
        LCD_data('H');
        LCD_data('E');
        LCD_data('L');
        LCD_data('L');
        LCD_data('O');
        delayMs(1000);

        // clear LCD display
        LCD_command(1);
        delayMs(1000);
    }
}

// initialize LCD controller
void LCD_init(void) {
    PORTS_init();

    delayMs(20);                // LCD controller reset sequence
    LCD_nibble_write(0x30, 0);
    delayMs(5);
    LCD_nibble_write(0x30, 0);
    delayMs(1);
    LCD_nibble_write(0x30, 0);
    delayMs(1);

    LCD_nibble_write(0x20, 0);  // use 4-bit data mode
    delayMs(1);
    LCD_command(0x28);          // set 4-bit data, 2-line, 5x7 font
    LCD_command(0x06);          // move cursor right
    LCD_command(0x01);          // clear screen, move cursor to home
    LCD_command(0x0F);          // turn on display, cursor blinking
}

/* PA2-PA5 for LCD D4-D7, respectively. 
 * PE0 for LCD R/S
 * PC6 for LCD EN
 */
void PORTS_init(void) {
    SYSCTL->RCGCGPIO |= 0x01;   // enable clock to GPIOA
    SYSCTL->RCGCGPIO |= 0x10;   // enable clock to GPIOE
    SYSCTL->RCGCGPIO |= 0x08;   // enable clock to GPIOD
    SYSCTL->RCGCGPIO |= 0x04;   // enable clock to GPIOC

    // PORTA 5-2 LCD D7-D4
    GPIOA->AMSEL &= ~0x3C;      // turn off analog of PORTA 5-2
    GPIOA->DATA &= ~0x3C;       // PORTA 5-2 output low
    GPIOA->DIR |= 0x3C;         // PORTA 5-2 as GPIO output pins
    GPIOA->DEN |= 0x3C;         // PORTA 5-2 as digital pins

    // PORTE 0 for LCD R/S
    GPIOE->AMSEL &= ~0x01;      // disable analog
    GPIOE->DIR |= 0x01;         // set PORTE 0 as output for CS
    GPIOE->DEN |= 0x01;         // set PORTE 0 as digital pins
    GPIOE->DATA |= 0x01;        // set PORTE 0 idle high

    // PORTC 6 for LCD EN
    GPIOC->AMSEL &= ~0x40;      // disable analog
    GPIOC->DIR |= 0x40;         // set PORTC 6 as output for CS
    GPIOC->DEN |= 0x40;         // set PORTC 6 as digital pins
    GPIOC->DATA &= ~0x40;       // set PORTC 6 idle low

    GPIOD->AMSEL &= ~0x80;      // disable analog
    GPIOD->DIR |= 0x80;         // set PORTD 7 as output for CS
    GPIOD->DEN |= 0x80;         // set PORTD 7 as digital pins
    GPIOD->DATA |= 0x80;        // set PORTD 7 idle high
}

void LCD_nibble_write(char data, unsigned char control) {
    /* populate data bits */
    GPIOA->DIR |= 0x3C;         // PORTA 5-2 as GPIO output pins
    GPIOA->DATA &= ~0x3C;       // clear data bits
    GPIOA->DATA |= (data & 0xF0) >> 2;  // set data bits

    /* set R/S bit */
    if (control & RS)
        GPIOE->DATA |= 1;
    else
        GPIOE->DATA &= ~1;
    
    /* pulse E */
    GPIOC->DATA |= 1 << 6;
    delayMs(0);
    GPIOC->DATA &= ~(1 << 6);
    
    GPIOA->DIR &= ~0x3C;        // PORTA 5-2 as GPIO input pins
}

void LCD_command(unsigned char command) {
    LCD_nibble_write(command & 0xF0, 0);    // upper nibble first
    LCD_nibble_write(command << 4, 0);      // then lower nibble

    if (command < 4)
        delayMs(2);         // command 1 and 2 needs up to 1.64ms
    else
        delayMs(1);         // all others 40 us
}

void LCD_data(char data) {
    LCD_nibble_write(data & 0xF0, RS);      // upper nibble first
    LCD_nibble_write(data << 4, RS);        // then lower nibble

    delayMs(1);
}


/* delay n milliseconds (50 MHz CPU clock) */
void delayMs(int n) {
    int i, j;
    for(i = 0 ; i< n; i++)
        for(j = 0; j < 6265; j++)
            {}  /* do nothing for 1 ms */
}