clock_generator/firmware/src/main.c

#define	F_CPU   8000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <stdbool.h>

#define SPI_PORT PORTB
#define SPI_DDR DDRB
#define SPI_SCK PB5
#define SPI_MOSI PB3
#define SPI_SS PB2

#define LCD_CD PB6
#define LCD_RST PB1

void spi_init(void) {
    SPI_DDR |= (1 << SPI_SCK) | (1 << SPI_MOSI) | (1 << SPI_SS);
    SPI_PORT |= (1 << SPI_SS);
    SPCR = (1 << SPE) | (1 << MSTR);
    SPSR = (1 << SPI2X);
}

uint8_t spi_byte(uint8_t data) {
   SPDR = data;
   while(!(SPSR & (1 << SPIF)));
   return SPDR;
 }

void lcd_write(uint8_t data) {
    SPI_PORT &= ~(1 << SPI_SS);
    spi_byte(data);
    SPI_PORT |= (1 << SPI_SS);
}

void lcd_init(void) {
    SPI_DDR |= (1 << LCD_CD) | (1 << LCD_RST);
    _delay_ms(1);
    SPI_PORT |= (1 << LCD_RST);
    _delay_ms(5);

    lcd_write(0x40); // (6)  Set Scroll Line: Display start line 0
    lcd_write(0xA1); // (13) Set SEG direction: SEG reverse
    lcd_write(0xC0); // (14) Set COM direction: Normal COM0 - COM63
    lcd_write(0xA6); // (11) Set Inverse Display: Display inverse off
    lcd_write(0xA2); // (17) Set LCD Bias Ratio: Set Bias 1/9 (Duty 1/65)
    lcd_write(0x2F); // (5)  Set Power Control: Booster, Regulator and Follower on
    lcd_write(0x27); // (8)  Set VLCD Resistor Ratio: Set Contrast
    lcd_write(0x81); // (9)  Set Electronic Volume: Set Contrast
    lcd_write(0x10); // (9)  Set Electronic Volume: Set Contrast
    lcd_write(0xAF); // (12) Set Display Enable: Display on
}

void lcd_fill(uint8_t data) {
    for (uint8_t i = 0; i < 8; i++) {
        SPI_PORT &= ~(1 << LCD_CD);
        lcd_write(0x00);
        lcd_write(0x10);
        lcd_write(0xB0 + i); // page address 0 + i

        SPI_PORT |= (1 << LCD_CD);

        for (uint8_t j = 0; j < 102; j++) {
            lcd_write(data);
        }
    }
}

int main(void) {
    // FastPWM: 1.25kHz
    TCCR0A = (1 << WGM01) | (1 << WGM00) | (1 << COM0B1);
    TCCR0B = (1 << CS01) | (1 << WGM02); // prescaler = 8;
    OCR0A = 100;
    OCR0B = 10;
    DDRD |= (1 << PD5);

    bool reverse = 0;

    spi_init();
    lcd_init();
    lcd_fill(0xFF);

    while (1) {
        _delay_ms(1);

        if (OCR0B > 100)
            reverse = !reverse;

        if (reverse)
            OCR0B++;
        else
            if (OCR0B > 0)
                OCR0B--;
            else
                reverse = !reverse;
    }
}