/* Initialize LCD controller and flash HELLO on LCD.
 *
 * The connections between the LCD controller of EduPad 
 * board and the MSP432 LaunchPad are
 *
 * P3.6 - D4  - J2-11 * PA2 - D4 - P3.6
 * P5.2 - D5  - J2-12 * PA3 - D5 - P5.2
 * P5.0 - D6  - J2-13 * PA4 - D6 - P5.0
 * P4.6 - D7  - J1-8  * PA5 - D7 - P6.4
 * P3.0 - R/S - J2-18 * PE0 - R/S - P3.0
 * P6.7 - EN  - J4-35 * PC6 - EN - P6.7
 * For simplicity, all delay below 1 ms uses 1 ms.
 *
 * Built and tested with MSP432P401R Rev. C, Keil MDK-ARM v5.24a and MSP432P4xx_DFP v3.1.0
 */

#include "msp.h"

#define RS 1        /* BIT0 mask for reg select */
#define EN 0x80     /* BIT7 mask for E */
#define BL 0x20     /* BIT5 mask for backlight */

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 SSI2 then 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 */
}

void PORTS_init(void) {
    P3->DIR |= 0x40;    /* LCD D4-D7 */
    P5->DIR |= 4;
    P5->DIR |= 1;
    P4->DIR |= 0x40;

    P3->DIR |= 1;       /* P3_0 for LCD R/S */
    P6->DIR |= 0x80;    /* P6_7 for LCD EN */
}

void LCD_nibble_write(char data, unsigned char control) {
    /* populate data bits */
    if (data & 0x10)
        P3->OUT |= 0x40;
    else
        P3->OUT &= ~0x40;

    if (data & 0x20)
        P5->OUT |= 4;
    else
        P5->OUT &= ~4;

    if (data & 0x40)
        P5->OUT |= 1;
    else
        P5->OUT &= ~1;

    if (data & 0x80)
        P4->OUT |= 0x40;
    else
        P4->OUT &= ~0x40;

    /* set R/S bit */
    if (control & RS)
        P3->OUT |= 1;
    else
        P3->OUT &= ~1;

    /* pulse E */
    P6->OUT |= 0x80;
    delayMs(0);
    P6->OUT &= ~0x80;
}

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);
}

/* system clock at 3 MHz, MSP432P401R Rev. C, Start-up v2.2.1 */
void delayMs(int n) {
    int i, j;

    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* Delay */
}