text: /*
      Copyright (c) 2007 Stefan Engelke <mbox@stefanengelke.de>
  
      Permission is hereby granted, free of charge, to any person 
      obtaining a copy of this software and associated documentation 
      files (the "Software"), to deal in the Software without 
      restriction, including without limitation the rights to use, copy, 
      modify, merge, publish, distribute, sublicense, and/or sell copies 
      of the Software, and to permit persons to whom the Software is 
      furnished to do so, subject to the following conditions:
  
      The above copyright notice and this permission notice shall be 
      included in all copies or substantial portions of the Software.
  
      THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
      EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
      MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
      NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 
      HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
      WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
      OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
      DEALINGS IN THE SOFTWARE.
  
      $Id$
  */
  
  #include <avr/io.h>
  #include <avr/interrupt.h>
  
  #define PORT_SPI    PORTB
  #define DDR_SPI     DDRB
  #define DD_MISO     DDB4
  #define DD_MOSI     DDB3
  #define DD_SS       DDB2
  #define DD_SCK      DDB5
  
  
  void spi_init()
  // Initialize pins for spi communication
  {
      DDR_SPI &= ~((1<<DD_MOSI)|(1<<DD_MISO)|(1<<DD_SS)|(1<<DD_SCK));
      // Define the following pins as output
      DDR_SPI |= ((1<<DD_MOSI)|(1<<DD_SS)|(1<<DD_SCK));
  
      
      SPCR = ((1<<SPE)|               // SPI Enable
              (0<<SPIE)|              // SPI Interupt Enable
              (0<<DORD)|              // Data Order (0:MSB first / 1:LSB first)
              (1<<MSTR)|              // Master/Slave select   
              (0<<SPR1)|(0<<SPR0)|    // SPI Clock Rate F_CPU/4
              (0<<CPOL)|              // Clock Polarity (0:SCK low / 1:SCK hi when idle)
              (0<<CPHA));             // Clock Phase (0:leading / 1:trailing edge sampling)
  
      SPSR = (1<<SPI2X);              // Double Clock Rate
      
  }
  
  void spi_transfer_sync (uint8_t * dataout, uint8_t * datain, uint8_t len)
  // Shift full array through target device
  {
         uint8_t i;      
         for (i = 0; i < len; i++) {
               SPDR = dataout[i];
               while((SPSR & (1<<SPIF))==0);
               datain[i] = SPDR;
         }
  }
  
  void spi_transmit_sync (uint8_t * dataout, uint8_t len)
  // Shift full array to target device without receiving any byte
  {
         uint8_t i;      
         for (i = 0; i < len; i++) {
               SPDR = dataout[i];
               while((SPSR & (1<<SPIF))==0);
         }
  }
  
  uint8_t spi_fast_shift (uint8_t data)
  // Clocks only one byte to target device and returns the received one
  {
      SPDR = data;
      while((SPSR & (1<<SPIF))==0);
      return SPDR;
  }
  
  