/* p3_2.c: Initialize and blink "HELLO" on the LCD using 8-bit data mode.
 *          Polling of the busy bit of the LCD status register is used.
 *
 * Data pins use Port B07-00, control pins use Port A06-04.
 *
 * 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_command_noPoll(unsigned char command);
void LCD_data(unsigned char data);
void LCD_init(void);
void LCD_ready(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) {
    int i;
    unsigned char* ARRAY_PORT_PINCFG1 = (unsigned char*)&REG_PORT_PINCFG1;

    REG_PORT_DIRSET0 = RS | RW | EN;    /* make PA06-04 pins output for control */
    REG_PORT_DIRSET1 = 0x000000FF;      /* make PB07-00 pins output for data */
    for (i = 0; i < 8; i++)
        ARRAY_PORT_PINCFG1[i] |= 2;     /* enable PB07-00 input buffer */

    delayMs(30);                /* initialization sequence */
    LCD_command_noPoll(0x30);	/* LCD does not respond to status poll yet */
    delayMs(5);
    LCD_command_noPoll(0x30);
    delayMs(1);
    LCD_command_noPoll(0x30);   /* busy flag cannot be polled before this command */

    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 */
}

/* This function waits until LCD controller is ready to
 * accept a new command/data before returns.
 * It polls the busy bit of the status register of the LCD controller.
 * In order to read the status register, the data port of the
 * microcontroller has to switch direction to input before reading
 * the LCD. The data port of the microcontroller is returned to
 * output port before the end of this function.
 */
void LCD_ready(void) {
    char status;

    /* change to read configuration to poll the status register */
    REG_PORT_DIRCLR1 = 0x000000FF;  /* make PB7-0 pins input */

    REG_PORT_OUTCLR0 = RS;          /* RS = 0 */
    REG_PORT_OUTSET0 = RW;          /* R/W = 1 */

    do {    /* stay in the loop until it is not busy */
        REG_PORT_OUTSET0 = EN;          /* pulse E high */
        delayMs(0);
        status = REG_PORT_IN1;          /* read status */
        REG_PORT_OUTCLR0 = EN;          /* clear E */
        delayMs(0);
    } while (status & 0x80);            /* check busy bit */

    /* return to default write configuration */
    REG_PORT_OUTCLR0 = RW;          /* R/W = 1 */
    REG_PORT_DIRSET1 = 0x000000FF;  /* make PB7-0 pins output */
}

/* This function waits for LCD controller ready before issuing
 * the next command.
 */
void LCD_command(unsigned char command) {
    LCD_ready();                    /* wait for LCD controller ready */
    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 */
}

/* This function is used at the beginning of the initialization
 * when the busy bit of the status register is not readable.
 */
void LCD_command_noPoll(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 */
}

/* This function waits for LCD controller ready before issuing
 * the next data.
 */
void LCD_data(unsigned char data) {
    LCD_ready();                    /* wait for LCD controller ready */
    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 */
}

/* 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");
}