tabby/avr/send.c

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

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

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

static tabby_printer_response response;

static uint8_t body[TABBY_PRINTER_PACKET_MAX_SIZE];

static uint16_t sum = 0x0000;

/*
 * So like, we're abusing pins here.  So badly, it's beyond.  So here's
 * what's going down: We want to retain the same physical I/O connections
 * between both the sending and receiving flavors of the whole Game Boy
 * Printer endeavor, and that mean/s that we must absolutely bit bang MOSI
 * and MISO opposite from their ordinary roles.  The reason being: There is
 * no notion of MISO or MOSI from the Game Boy's (nor its peripherals')
 * point of view. The SI and SO pins over a link cable are crossed over, so
 * SI on one end always connects to SO on the other, and vice-versa.  The SI
 * and SO pins do not switch roles based on role, unlike on AVR SPI
 * implementations.
 */
static void spi_init() {
    SC_OUTPUT();
    SO_OUTPUT();

    SI_INPUT();
    SI_PULLUP();

    SC_HIGH();
    SO_LOW();
}

static uint8_t spi_send_byte(uint8_t value) {
    uint8_t i, ret = 0;

    for (i=0; i<8; i++) {
        SC_LOW();

        if (value & 0x80) {
            SO_HIGH();
        } else {
            SO_LOW();
        }

        _delay_us(SPI_PULSE_USEC);

        ret   <<= 1;
        value <<= 1;

        if (SI_IS_HIGH()) {
            ret |= 1;
        }

        SC_HIGH();

        _delay_us(SPI_PULSE_USEC);
    }

    return ret;
}

static void spi_send_packet() {
    int i;

    for (i=0; i<sizeof(header); i++) {
        (void)spi_send_byte(header.data[i]);
    }

    for (i=0; i<header.size; i++) {
        (void)spi_send_byte(body[i]);
    }

    (void)spi_send_byte( sum & 0x00ff);
    (void)spi_send_byte((sum & 0xff00) >> 8);

    response.device = spi_send_byte(0);
    response.status = spi_send_byte(0);
}

int main() {
    uint16_t i = 0,
             b = 0;

    uint8_t c;

    uart_init();
     spi_init();

    sei();

    while (1) {
        uart_putchar('O', NULL);

        c = uart_getchar(NULL);

        if (c == 'K') {
            break;
        }
    }

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

        switch (i) {
            case 0: {
                if (c == TABBY_PRINTER_SYNC_1) {
                    header.data[0] = c;
                    i++;

                    b = 0;
                }

                break;
            }

            case 1: {
                if (c == TABBY_PRINTER_SYNC_2) {
                    header.data[1] = c;
                    i++;
                } else {
                    i = 0;
                }

                break;
            }

            case 2: {
                switch (c) {
                    case TABBY_PRINTER_PACKET_INIT:
                    case TABBY_PRINTER_PACKET_JOB:
                    case TABBY_PRINTER_PACKET_DATA:
                    case TABBY_PRINTER_PACKET_CANCEL:
                    case TABBY_PRINTER_PACKET_INQUIRY: {
                        header.type = c;
                        i++;

                        break;
                    }

                    default: {
                        i = 0;

                        break;
                    }
                }

                break;
            }

            case 3: {
                header.compression = c;
                i++;

                break;
            }

            case 4: {
                header.size = c;
                i++;

                break;
            }

            case 5: {
                header.size |= c << 8;
                i++;

                break;
            }

            default: {
                if (b < header.size) {
                    body[b++] = c;
                } else if (b == header.size) {
                    sum = c;
                    b++;
                } else if (b == header.size + 1) {
                    sum |= c << 8;

                    i = 0;
                    b = 0;

                    spi_send_packet();

                    uart_putchar(response.device, NULL);
                    uart_putchar(response.status, NULL);
                }
            }
        }
    }

    return 0;
}