/* Initialize LCD controller and flash HELLO on LCD.
 *
 * The LCD controller of Wytec EduPad board is connected to
 * a shift register which is connected to UCB0 in SPI mode.  
 * P6.7 is used for slave select of the shift register.
 *
 * The connections between the shift register and LCD are
 * Bit 0 - RS (register select)
 * Bit 1 - E (enable)
 * Bit 2 - 
 * Bit 4 - Data 4
 * Bit 5 - Data 5
 * Bit 6 - Data 6
 * Bit 7 - Data 7
 *
 * 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 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 UCB0_Write(unsigned char data);

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 UCB0 then initialize LCD controller
void LCD_init(void) {
    EUSCI_B0->CTLW0 = 0x0001;
    EUSCI_B0->CTLW0 = 0xE9C1;
    EUSCI_B0->CTLW0 &= ~0x0001;

    P1->SEL0 |= 0x60;           /* P1.5, P1.6 for UCB0 */
    P1->SEL1 &= ~0x60;

    /* PP6.7 as slave select */
    P6->DIR |= 0x80;            /* P6.7 set as output */
    P6->OUT |= 0x80;            /* /SS idle high */

    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 UCB0_Write(unsigned char data) {
    P6->OUT &= ~0x80;           // assert chip select
    EUSCI_B0->TXBUF = data;               /* write data */
    while(EUSCI_B0->STATW & 0x01) ;       /* wait for transmit done */
    P6->OUT |= 0x80;            // deassert chip select
}

void LCD_nibble_write(char data, unsigned char control) {
    data &= 0xF0;           // clear lower nibble for control
    control &= 0x0F;        // clear upper nibble for data
    UCB0_Write (data | control);           // RS = 0, R/W = 0
    UCB0_Write (data | control | EN);      // pulse E
    delayMs(0);
    UCB0_Write (data);
}

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 */
void delayMs(int n) {
    int i, j;

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