/* p3_3.c: Initialize and display "hello" on the LCD using 4-bit data mode.
 *         It uses delay to wait out the time LCD controller is busy.
 *
 * Data and control pins share Port B07-00.
 * 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 0x01     /* PB00 mask for Register Select*/
#define EN 0x04     /* PB02 mask for Enable */

void delayMs(int n);
void LCD_nibble_write(unsigned char data, unsigned char control);
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_DIRSET1 = 0xFF;    /* make PB07-00 pins output for data and controls */
    delayMs(30);                /* initialization sequence */
    LCD_nibble_write(0x30, 0);
    delayMs(10);
    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 after each char */
    LCD_command(0x01);          /* clear screen, move cursor to home */
    LCD_command(0x0F);          /* turn on display, cursor blinking */
}

/* With 4-bit mode, each command or data is sent twice with the upper 
 * nibble first then the lower nibble.
 */
void LCD_nibble_write(unsigned char data, unsigned char control) {
    data &= 0xF0;               /* clear lower nibble for control */
    control &= 0x0F;            /* clear upper nibble for data */
    REG_PORT_OUTCLR1 = 0xFF;    /* clear data bus */
    REG_PORT_OUTSET1 = data | control;  /* RS = 0, R/W = 0 */
    REG_PORT_OUTSET1 = EN;              /* pulse E */
    delayMs(0);
    REG_PORT_OUTCLR1 = EN;              /* clear E */
}

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(4);         /* commands 1, 2 need up to 1.64ms */
    else
        delayMs(1);         /* all others 40 us */
}

void LCD_data(unsigned char data) {
    LCD_nibble_write(data & 0xF0, RS);    /* upper nibble first */
    LCD_nibble_write(data << 4, RS);      /* then lower nibble  */
    
    delayMs(1);
}

/* 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");
}