/* Drive an HD44780 LCD display in 4-bit mode.
   Adam Sampson <ats@offog.org>
 */

#include <avr/io.h>
#include <stdbool.h>
#include <stdint.h>

#include "lcd.h"

static const uint8_t lcd_mask = _BV(LCD_E) | _BV(LCD_RS) | (0xF << LCD_D4);

// Busy-wait for at least the given number of ms.
void lcd_delay(uint16_t ms) {
	while (--ms != 0) {
		uint16_t i = (F_CPU / 1000) / 4;
		__asm__ __volatile__ (
			"1:\tsbiw %0,1\n"
			"\tbrne 1b\n"
			: "=w" (i)
			: "0" (i));
	}
}

static void lcd_nibble(uint8_t nibble, bool is_cmd) {
	uint8_t v = nibble << LCD_D4;
	if (!is_cmd)
		v |= _BV(LCD_RS);

	LCD_PORT = (LCD_PORT & ~lcd_mask) | v | _BV(LCD_E);
	lcd_delay(1);
	LCD_PORT &= ~_BV(LCD_E);
	lcd_delay(2);
}

void lcd_word(uint8_t word, bool is_cmd) {
	lcd_nibble((word >> 4) & 0xF, is_cmd);
	lcd_nibble(word & 0xF, is_cmd);
}

void lcd_clear() {
	lcd_word(CMD_CLEAR, true);
	lcd_delay(4);
}

void lcd_move(uint8_t x, uint8_t y) {
	lcd_word(CMD_SETDD | (0x40 * y) | x, true);
}

void lcd_puts(const char *s) {
	while (*s != '\0')
		lcd_word(*s++, false);
}

void lcd_init() {
	// Set the LCD pins to be outputs.
	LCD_DDR |= lcd_mask;

	lcd_delay(20);

	for (int i = 0; i < 3; i++) {
		lcd_nibble((CMD_FUNCSET | FUNCSET_DL) >> 4, true);
		lcd_delay(5);
	}
	lcd_nibble(CMD_FUNCSET >> 4, true);

	lcd_word(CMD_FUNCSET | FUNCSET_N, true);
	lcd_word(CMD_DISPCTL | DISPCTL_D, true);
	lcd_word(CMD_ENTRYSET | ENTRYSET_ID, true);

	lcd_clear();
}