/*
 * Initialize LCD controller and flash HELLO on LCD.
 * The LCD controller of Wytec EduBase board is connected to
 * a shift register on SPI0 of FRDM-KL25Z.  PTA13 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 - Backlight enable
 * Bit 4 - Data 4
 * Bit 5 - Data 5
 * Bit 6 - Data 6
 * Bit 7 - Data 7
 *
 * For simplicity, all delay below 1 ms uses 1 ms.
 *
 */

#include "MKL25Z4.h"

#define RS 1    // BIT0 mask for reg select
#define EN 2    // BIT1 mask for E
#define BL 4    // BIT2 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 SPI0_init(void);
void SPI0_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 SSI2 then initialize LCD controller
void LCD_init(void)
{
    SPI0_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 SPI0_init(void) {
    SIM->SCGC5 |= 0x1000;       /* enable clock to Port D */
    PORTD->PCR[1] = 0x200;      /* make PTD1 pin as SPI SCK */
    PORTD->PCR[2] = 0x200;      /* make PTD2 pin as SPI MOSI */
    PORTD->PCR[0] = 0x100;      /* make PTD0 pin as GPIO */

    SIM->SCGC4 |= 0x400000;     /* enable clock to SPI0 */
    SPI0->C1 = 0x10;            /* disable SPI and make SPI0 master */
    SPI0->BR = 0x60;            /* set Baud rate to 1 MHz */
    SPI0->C1 |= 0x40;           /* Enable SPI module */

    SIM->SCGC5 |= 0x0200;       /* enable clock to Port A */
    PORTA->PCR[13] = 0x100;     /* make PTA13 pin as GPIO */
    PTA->PDDR |= 1 << 13;       /* make PTA13 as output pin for /SS */
    PTA->PSOR = 1 << 13;        /* make PTA13 idle high */
}

void SPI0_write(unsigned char data) {
    volatile char dummy;

    PTA->PCOR = 1 << 13;              /* assert /SS */

    while(!(SPI0->S & 0x20)) { }    /* wait until tx ready */
    SPI0->D = data;                 /* send data byte */
    while(!(SPI0->S & 0x80)) { }    /* wait until tx complete */
    dummy = SPI0->D;                /* clear SPRF */

    PTA->PSOR = 1 << 13;              /* deasssert /SS */
}

void LCD_nibble_write(char data, unsigned char control)
{
    data &= 0xF0;       // clear lower nibble for control
    control &= 0x0F;    // clear upper nibble for data
    SPI0_write(data | control | BL);           // RS = 0, R/W = 0
    SPI0_write(data | control | EN | BL);      // pulse E
    delayMs(0);
    SPI0_write(data | BL);
    SPI0_write(BL);
}

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 (141.94MHz CPU clock)
void delayMs(int n)
{
    int i, j;
    for(i = 0 ; i < n; i++)
        for(j = 0; j < 7000; j++)
            {}  /* do nothing */
}