tabby/avr/send.c

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

#include <tabby/printer.h>
#include <tabby/avr/uart.h>

#define TIMER0_INTERVAL 1953

static volatile uint8_t bits      = 0;
static volatile uint8_t value_in  = 0x00; /* Data coming in from Game Boy */
static volatile uint8_t value_out = 0x00; /* Data going out to Game Boy */

static volatile tabby_printer_packet header = {
    .type        = 0,
    .compression = 0,
    .size        = 0
};

static volatile uint16_t i = 0,
                         b = 0;

/*
 * Internal clock source interrupt vector
 */
ISR(TIMER0_COMPB_vect) {
    value_in >>= 1;

    PORTB |= (1 << PORTB5);

    if (PORTB & (1 << PORTB4)) {
        value_in |= 0x80;
    }

    if (value_out & 0x80) {
        PORTB |=  (1 << PORTB3);
    } else {
        PORTB &= ~(1 << PORTB3);
    }

    value_out <<= 1;

    if (--bits == 0) {
        bits = 8;
    }

    /*
     * Chill out for 60µsec, then ride out the rest of the time until the next
     * interrupt with a high as fuck SCK
     */
    _delay_us(60);

    PORTB &= ~(1 << PORTB5);
}

static void clock_setup() {
    /*
     * Configure MISO as output
     */
    DDRB |= (1 << DDB4);

    /*
     * Configure MOSI as input
     */
    DDRB &= ~(1 << DDB3);

    /*
     * Configure SCK pin as output
     */
    DDRB |= (1 << DDB5);

    /*
     * Enable timer interrupt vector
     */
    TIMSK0 = (1 << TOIE1);

    /*
     * Reset timer counter to zero
     */
    TCNT1 = 0;

    /*
     * Set timer interval
     */
    OCR1A = TIMER0_INTERVAL;

    /*
     * Set timer clock divider to 1/1
     */
    TCCR1B = (1 << CS10);
}

int main() {
    uart_init();

    clock_setup();

    sei();

    while (1) {
        uint8_t c = uart_getchar(NULL);

    }

    return 0;
}