// Using the spinner board to test 328 counters
 
#include <SPI.h>
 
const int HALL  =  2; // PD2
const int BLANK =  8; // PB0
const int LAT   =  9; // PB1
 
const int HALL_INT = 0; // Hall effect interrupt 0 on PD2 (INT0)
 
unsigned int savedCounter = 0;
unsigned int slice = 0;
 
void hallStart(void) {
  // TCNT1 is counts per full revolution
  savedCounter = TCNT1;
  TCNT1 = 0;
 
  // Also reset TCNt2 (slice counter) so we always start in a known
  // state
  TCNT2 = 0;
 
  // Calculate a new compare value for timer 2 based on how fast our last revolution was.
  // 512 angle slices, so divide the savedCounter by 512 to get the count per slice
  // But we also have a /8 prescaler, so instead divide by 4096
  int sliceCount = savedCounter / 4096;
 
  // Saved the new slice counter
  OCR2A = sliceCount;  
 
  // Reset the slice number
  slice = 0;
 
  // Now start the 8 bit counter 2
  TCCR2B = 6;                   // Set /256 prescaler
}
 
// ISR for the timer to switch the LEDs
ISR(TIMER2_COMPA_vect)
{
  if (slice == 0 || slice == 128 || slice == 256 || slice == 384)
  {
    setLeds(0xFFFF);
  }
  else if (slice == 1 || slice == 129 || slice == 257 || slice == 385)
  {
    setLeds(0x0001);
  }
 
  slice++;
}
 
void setup() {
  digitalWrite(LAT, LOW);
  pinMode(LAT, OUTPUT);     
 
  digitalWrite(BLANK, HIGH);
  pinMode(BLANK, OUTPUT);     
 
  pinMode(HALL, INPUT_PULLUP);
 
  // Setup the 16 bit counter counter 1
  TCCR1A = 0;                   // Turn off output compare modes
  TCCR1B = 2;                   // Turn on clk/8 prescaler
 
  // Setup 8 bit counter 2
  TCCR2A = 2;                   // CTC mode
  TCCR2B = 0;                   // Start with timer off
  TIMSK2 = 2;                   // Enable Output Compare A interrupt
 
  attachInterrupt(HALL_INT, hallStart, FALLING);
 
  SPI.begin();
  SPI.setDataMode(SPI_MODE0);
  SPI.setBitOrder(LSBFIRST);
  SPI.setClockDivider(SPI_CLOCK_DIV2); // Datasheet says 35 MHz max, so 8 MHz is fine
 
  TCNT1 = 0;
}
 
void setLeds(unsigned int pattern) {
  // Blank the LEDS
  digitalWrite(BLANK, HIGH);
 
  // Transfer the data
  SPI.transfer(pattern & 0xFF);
  SPI.transfer(pattern >> 8);
 
  // Latch the data
  digitalWrite(LAT, HIGH);
  digitalWrite(LAT, LOW);
 
  // Unblank the LEDS
  digitalWrite(BLANK, LOW);
}
 
void loop() {
  // That's right--nothing to do here
}