tabby/avr/recv.c

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

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

static volatile tabby_printer_packet header;

static volatile uint16_t i, b;

/*
 * SPI byte receipt interrupt vector
 */
ISR(SPI_STC_vect) {
    uint8_t in  = SPDR,
            out = 0;

    uart_putchar(in, NULL);

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

                b = 0;
            }

            break;
        }

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

            break;
        }

        case 2: {
            header.type = in;
            i++;

            break;
        }

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

            break;
        }

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

            break;
        }

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

            if (header.size > TABBY_PRINTER_PACKET_MAX_SIZE) {
                i = 0;
            }

            break;
        }

        default: {
            if (b <= header.size) {
                b++;
            } else if (b == header.size + 1) {
                b++;

                out = TABBY_PRINTER_DEVICE_ID;
            } else if (b == header.size + 2) {
                b++;

                out = TABBY_PRINTER_OK;
            } else if (b == header.size + 3) {
                i = 0;
            }
        }
    }

    SPDR = out;
}

static void spi_init() {
    SS_INPUT();
    SC_INPUT();
    SI_INPUT();
    SO_OUTPUT();

    /*
     * Set SPI slave mode, and shift in/out most significant bit first
     */
    SPCR &= ~((1 << MSTR) | (1 << DORD));

    /*
     * Enable SPI in Mode 3 with interrupts, clock nominally high, output on
     * falling edge, input on rising edge
     */
    SPCR |= (1 << CPOL) | (1 << CPHA) | (1 << SPIE) | (1 << SPE);

    /*
     * Initialize the SPI Data Register and serial buffer
     */
    SPDR = 0;
}

int main() {
    uart_init();
     spi_init();

    sei();

    while (1) {
        sleep_mode();
    }

    return 0;
}