git.defcon.no Git - AVRduinoSPI-example/blob - slave/slave.ino

   1 // Interrupt-driven SPI SLAVE example
   2 // Recieves bytes over SPI and stuffs them in
   3 // a sort-of-circular-buffer that is printed to Serial.
   4 // Uses a mix of Arduino and plain AVR code,
   5 // but does not use the Arduino SPI library.
   6
   7 #include <avr/interrupt.h>
   8
   9 volatile uint8_t buffer[16];
  10 volatile uint8_t bptr;
  11
  12
  13 void setup()
  14 {
  15   Serial.begin(115200);
  16   Serial.println("Hello from SLAVE")
  17
  18     // A nice little debug/status pin, set as OUTPUT using the Arduino-way ;)
  19     pinMode(7,  OUTPUT);
  20
  21   // Make sure our buffer-pointer starts at the first buffer byte (pos 0)
  22   bptr = 0;
  23
  24   // Set MISO as OUTPUT using the AVR-way ;)
  25   DDRB=(1<<DDB4);
  26   // Enable SPI (default Slave) and enable SPI interrupts
  27   SPCR=(1<<SPE)|(1<<SPIE);
  28
  29   // Activate interrupts
  30   sei();
  31 }
  32
  33 void loop()
  34 {
  35   // In the main loop, simply output the buffer contents, over and over again..
  36   Serial.print("b ");
  37   for ( uint8_t i = 0; i <= 15; i++ )
  38   {
  39     Serial.print(i);
  40     Serial.print(" = ");
  41     Serial.print(buffer[i]);
  42     Serial.print("  ");
  43   }
  44   Serial.println(" ... ");
  45   delay(500);
  46 }
  47
  48 // The ISR for SPI Serial Transfer Complete gets triggered
  49 // on each byte transferred.
  50 ISR(SPI_STC_vect)
  51 {
  52   // Put data in buffer, increment buffer pointer, wrap around on end.
  53   buffer[bptr] = spi_read();
  54   bptr++;
  55   if (bptr > 15) bptr = 0;
  56 }
  57
  58 uint8_t spi_read( ){
  59   // Getting the transferred byte is as imple as reading the Data Register
  60   // each time a byte has completed transfer. This and the ISR, needs to be
  61   // quick, so that the next byte does not overwrite the current one.
  62
  63   // Sending is done by setting the data register before reading ...
  64   SPDR = 0;
  65   uint8_t d = SPDR;
  66
  67   // Let's add some fun "things happen because of transfers"...
  68   if ( d == 45 ) digitalWrite(7, ( !digitalRead(7) ) );
  69
  70   return d;
  71 }
  72
  73
  74