source: avrstuff/V-USB_Dev/firmwares/CrO2/main.c@ 4af90bf

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

#include <string.h>
#include <stdbool.h>

#include "usbdrv/usbdrv.h"

static uint8_t ioblock[275]; // Max. Size of an MO5 standard block including sync header
static uint8_t status; // status bits
static uint16_t writePos;
static uint16_t blksz;

static uint16_t readPos;
static uint8_t bitpos;
static uint8_t bit; // Currently generated bit

int main() {
        // Init
        status = 0;
        writePos = 0;
        blksz = 0;

        wdt_enable(WDTO_2S);

        // USB
        usbInit();
        sei();

        bit = 1;
        bitpos = 0;
        readPos = 0;

        // Setup TIMER 1 for MFM pulses generation
        TCCR1A = (1<<COM1A0); // Enable OC1A output
        // CTC mode with OCR1A as MAXregister
        TCCR1B = (1<<WGM12) | (1<<CS10);
        OCR1A = 12800; // 800us bit clock
        OCR1B = 6400; // Half-clock for 1 bits
        TIMSK = (1 << OCIE1B) | (1 << OCIE1A); // interrupts on both timer matches.

        // TODO only start the timer when actually needed (start of block)
        // and stop it when done.
        DDRB |= 2; // OC1A/PB1 as output


        while(1) {
                wdt_reset();
                usbPoll();

                // TODO send data to tape !
        }
}


uint8_t usbFunctionSetup(uint8_t data[8]) {
        usbRequest_t *rq = (void *)data;

        usbMsgPtr = ioblock;
        switch(rq->bRequest)
        {
                case 0:
                        {  /* CONFIGURE */
                                status = rq->wValue.bytes[0];
                                return 0;
                        }
                case 1:
                        {  /* RECEIVE/POLL DATA (TAPE > USB) */
                                return 254; 
                        }
                case 2:
                        {
                                /* SEND DATA (USB > TAPE) */
                                /* Get ready, actual data will come in usbFunctionWrite */
                                // TODO store type of MO5 block + size in ioblock
                                writePos = 0;
                                blksz = rq->wLength.word;
                                return USB_NO_MSG; // Call usbFunctionWrite to send the data
                        }
        }
        return 0;
}

uint8_t usbFunctionWrite(uint8_t* data, uint8_t len)
{
        // The data for a single request will be sent as slices of up to 8 bytes.
        for (int i = 0; i < len; i++)
        {
                // TODO leave place for sync header and block type+size
                ioblock[writePos++] = data[i];
        }

        // TODO compute checksum as we go

        return writePos>= blksz ? 1:0;
        // returns 0: "needs more data"
        // returns 1: "done"
        // returns FF: "error"
}

ISR (TIMER1_COMPA_vect)
{
        // generate next bit
        bit = (ioblock[readPos] >> bitpos) & 1;
        bitpos++;
        if (bitpos > 7)
        {
                bitpos = 0;
                readPos++;
                if (readPos > 270)
                        readPos = 0; // TODO stop timer
        }
}

ISR (TIMER1_COMPB_vect)
{
        TCCR1A |= (bit << FOC1A); // Force toggle of A on B compare when generating a 1 bit
}