/*

* ----------------------------------------------------------------------------

* "THE BEER-WARE LICENSE" (Revision 42):

* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you

* can do whatever you want with this stuff. If we meet some day, and you think

* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch

* ----------------------------------------------------------------------------

*

* HD44780 LCD display driver

*

* Modified for a custom 8-bit mode (v2) by Urja Rannikko 2010.

* Pinout of this 8-bit mode:

* E = PD7, LED backlight = PD6, RW = PD1, RS = PD4, contrast = PD5. PORTB = data port.

*

* The LCD controller is used in 8-bit mode with a full bi-directional

* interface (i.e. R/~W is connected) so the busy flag can be read.

*

*/

#include "main.h"

#include <stdbool.h>

#include <stdint.h>

#include <avr/io.h>

#include <util/delay.h>

#include "hd44780.h"

#define HD44780_BUSYFLAG 0x80

#define LCD_E _BV(7)

#define LCD_RW _BV(1)

#define LCD_RS _BV(4)

/*

* Send one pulse to the E signal (enable). Mind the timing

* constraints. If readback is set to true, read the HD44780 data

* pins right before the falling edge of E, and return that value.

*/

static inline uint8_t

hd44780_pulse_e(bool readback) __attribute__((always_inline));

static inline uint8_t

hd44780_pulse_e(bool readback)

{

uint8_t x;

PORTD |= LCD_E;

/*

* Guarantee at least 500 ns of pulse width. For high CPU

* frequencies, a delay loop is used. For lower frequencies, NOPs

* are used, and at or below 1 MHz, the native pulse width will

* already be 1 us or more so no additional delays are needed.

*/

#if F_CPU > 4000000UL

_delay_us(0.5);

#else

/*

* When reading back, we need one additional NOP, as the value read

* back from the input pin is sampled close to the beginning of a

* CPU clock cycle, while the previous edge on the output pin is

* generated towards the end of a CPU clock cycle.

*/

if (readback)

__asm__ volatile("nop");

# if F_CPU > 1000000UL

__asm__ volatile("nop");

# if F_CPU > 2000000UL

__asm__ volatile("nop");

__asm__ volatile("nop");

# endif /* F_CPU > 2000000UL */

# endif /* F_CPU > 1000000UL */

#endif

if (readback)

x = PINB;

else

x = 0;

PORTD &= ~LCD_E;

return x;

}

/*

* Send one byte to the LCD controller.

*/

void

hd44780_outbyte(uint8_t b, uint8_t rs)

{

PORTD &= ~LCD_RW; // RW

if (rs)

PORTD |= LCD_RS; // RS

else

PORTD &= ~LCD_RS; // RS

PORTB = b;

(void)hd44780_pulse_e(false);

}

/*

* Read one byte from the LCD controller.

*/

uint8_t

hd44780_inbyte(uint8_t rs)

{

uint8_t x;

PORTD |= LCD_RW; // RW

DDRB = 0; // DATABUS IN

if (rs)

PORTD |= LCD_RS; // RS

else

PORTD &= ~LCD_RS; // RS

x = hd44780_pulse_e(true);

DDRB = 0xFF; // DATABUS OUT

PORTD &= ~LCD_RW;

return x;

}

/*

* Wait until the busy flag is cleared.

*/

void

hd44780_wait_ready(void)

{

uint16_t cnt=30000; // With 1us/read this is 30ms+, should be enough.

while ((hd44780_incmd() & HD44780_BUSYFLAG)&&(cnt)) cnt--;

}

/*

* Initialize the LCD controller.

*

* The initialization sequence has a mandatory timing so the

* controller can safely recognize the type of interface desired.

* This is the only area where timed waits are really needed as

* the busy flag cannot be probed initially.

*/

void

hd44780_init(void)

{

DDRB = 0xFF; // Data port out

DDRD = 0xF2; // (comment was obsolete)

_delay_ms(15); /* 40 ms needed for Vcc = 2.7 V */

hd44780_outcmd(HD44780_FNSET(1, 0, 0));

_delay_ms(4.1);

hd44780_outcmd(HD44780_FNSET(1, 0, 0));

_delay_ms(0.1);

hd44780_outcmd(HD44780_FNSET(1, 0, 0));

hd44780_outcmd(HD44780_FNSET(1, 1, 0));

hd44780_wait_ready();

hd44780_outcmd(HD44780_FNSET(1, 1, 0));

hd44780_wait_ready();

hd44780_outcmd(HD44780_DISPCTL(0, 0, 0));

hd44780_wait_ready();

}