/* p3_1.c: Initialize and blink "Hello" on the LCD using 8-bit data mode.
 *         It uses delay to wait out the time LCD controller is busy.
 *
 * Data pins use Port B07-00, control pins use Port A06-04.
 * This program does not poll the status of the LCD.
 * Timing is more relax than the HD44780 datasheet to accommodate the
 * variations among the LCD modules.
 * You may want to adjust the amount of delay to optimize performance.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a
 */

#include "samd21.h"

#define RS 0x10     /* PA04 mask for Register Select*/
#define RW 0x20     /* PA05 mask for Read/Write */
#define EN 0x40     /* PA06 mask for Enable */

void delayMs(int n);
void LCD_command(unsigned char command);
void LCD_data(unsigned char data);
void LCD_init(void);

int main(void) {
    LCD_init();

    for(;;) {
        LCD_command(1);     /* clear display */
        delayMs(500);
        LCD_command(0x80);  /* set cursor at beginning of first line */
        LCD_data('H');      /* write the word "Hello" */
        LCD_data('e');
        LCD_data('l');
        LCD_data('l');
        LCD_data('o');
        delayMs(500);
    }
}

void LCD_init(void) {
    REG_PORT_DIRSET0 = RS | RW | EN;    /* make PA06-04 pins output for control */
    REG_PORT_DIRSET1 = 0x000000FF;      /* make PB07-00 pins output for data */

    delayMs(30);            /* initialization sequence */
    LCD_command(0x30);
    delayMs(10);
    LCD_command(0x30);
    delayMs(1);
    LCD_command(0x30);

    LCD_command(0x38);      /* set 8-bit data, 2-line, 5x7 font */
    LCD_command(0x06);      /* move cursor right after each char */
    LCD_command(0x01);      /* clear screen, move cursor to home */
    LCD_command(0x0F);      /* turn on display, cursor blinking */
}

/* send a command to the LCD controller */
void LCD_command(unsigned char command) {
    REG_PORT_OUTCLR0 = (RS | RW);   /* RS = 0, R/W = 0 */
    REG_PORT_OUTCLR1 = 0xFF;        /* clear data bus */
    REG_PORT_OUTSET1 = command;     /* put command on data bus */
    REG_PORT_OUTSET0 = EN;          /* pulse E high */
    delayMs(0);
    REG_PORT_OUTCLR0 = EN;          /* clear E */
    if (command < 4)
        delayMs(4);                 /* command 1, 2 need up to 1.64ms */
    else
        delayMs(1);                 /* all others 40 us */
}

/* send a byte of data to the LCD controller */
void LCD_data(unsigned char data) {
    REG_PORT_OUTSET0 = RS;          /* RS = 1 */
    REG_PORT_OUTCLR0 = RW;          /* R/W = 0 */
    REG_PORT_OUTCLR1 = 0xFF;        /* clear data bus */
    REG_PORT_OUTSET1 = data;        /* put command on data bus */
    REG_PORT_OUTSET0 = EN;          /* pulse E high */
    delayMs(0);
    REG_PORT_OUTCLR0 = EN;          /* clear E */
    delayMs(1);                     /* delay 40 us */
}

/* millisecond delay based on 1 MHz system clock */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 199; i++)
            __asm("nop");
}