arduino1 USB SPI bridge

// Written by Nick Gammon and Matthias Bock
// Licensed as GNU GPL v2

/*
 * For some reason this script won't read in the data ...
 */

/**
 * Send arbitrary number of bits at whatever clock rate (tested at 500 KHZ and 500 HZ).
 * This script will capture the SPI bytes, when a '\n' is recieved it will then output
 * the captured byte stream via the serial.
 */

/*
 * http://arduino.cc/en/Reference/SPI
 *
 * Arduino Mega2560 SPI pins:
 *  MISO: 50
 *  MOSI: 51
 *  SCK:  52
 *  SS:   53
 */
#include <SPI.h>

char buf [100];
volatile byte pos;
volatile boolean process_it;

void setup (void)
{
  // setup USB-serial port
  Serial.begin (9600);
  Serial.println("arduino1 slave");

  // receive on master out / slave in
  pinMode(MOSI, INPUT);

  // send on master in / slave out
  pinMode(MISO, OUTPUT);

  // turn SPI on
  SPCR |= 1 << SPE;

  // switch to slave mode
  SPCR &= 0xff - (1 << MSTR);

  // most significant bit first
  SPI.setBitOrder(MSBFIRST);

  // the base value of the clock is LOW: polarity=0
  // data is captured on the clock's rising edge: phase=0
  SPI.setDataMode(SPI_MODE1);

  // SPI sampling frequency as a fraction of the 16 MHz crystal
  // 16 MHz / 16 = 1 MHz
  SPI.setClockDivider(SPI_CLOCK_DIV16);

  // get ready for an interrupt
  pos = 0;   // buffer empty
  process_it = false;

  // now turn on interrupts
  SPI.attachInterrupt();

  // the rest of the magic is done in SPI.h
}

// SPI interrupt service routine
ISR (SPI_STC_vect)
{
    // grab byte from SPI Data Register
    byte c = SPDR;

    // add to buffer if room
    if (pos < sizeof buf)
    {
    buf [pos++] = c;

    // example: newline means time to process buffer
    if (pos >= 64)
        buf [pos] = 0;
        pos = 0;
        process_it = true;
    }
}

void loop (void)
{
    // wait for flag set in interrupt routine
    if (process_it)
    {
        for (int i=0; i<8; i++)
        {
          Serial.print( int(buf[i]) );
          Serial.print("-");
        }
        Serial.println();
        process_it = false;
    }
}