// Scope test for fast shiftOut function.
#include <DigitalIO.h>

// Create clockPin in output mode with inital level LOW.
DigitalPin<12> clockPin(OUTPUT, LOW);

// Create dataPin in output mode with inital level HIGH.
DigitalPin<13> dataPin(OUTPUT, HIGH);

//------------------------------------------------------------------------------
// Time to send one bit is ten cycles or 625 ns for 16 MHz CPU.
inline __attribute__((always_inline))
void sendBit(uint8_t bit, uint8_t data) {
  dataPin = data & (1 << bit);
  clockPin = 1;
  // may want a nop here - clock pulse is 125 ns wide
  clockPin = 0;
}
//------------------------------------------------------------------------------
// Time to send one byte is 5 usec.
void shiftOut(uint8_t bits) {
  sendBit(7, bits);
  sendBit(6, bits);  
  sendBit(5, bits);  
  sendBit(4, bits);
  sendBit(3, bits);
  sendBit(2, bits);
  sendBit(1, bits); 
  sendBit(0, bits); 
}
//------------------------------------------------------------------------------
void setup() {
  // Not used.
}
//------------------------------------------------------------------------------
void loop() {
  shiftOut(0X55);
  delay(2);
}