NCO c++ template

nco.cpp

// vim: set ts=2 sw=2 expandtab list
/*
 * File: nco.cpp
 * Description: NCO c++ template and testdriver
 * 
 * Author: rick kimball
 *
 * g++ -DDEBUG -Wall -Os -g nco.cpp -o nco
 */


#include <stdio.h>

//const long clk_in_freq = 16000000; // a 16MHz clock
const long clk_in_freq = 1000; // a 1k clock

/*
 * default_signal_handler - minimum signal_out functions for NCO
 * 
 * void toggle() - called each time an NCO edge is reached
 *                 occurs at 2x the NCO desired frequency out
 */
typedef struct {
  void toggle(void) {}  /* called by NCO each edge of our oscillator */
} default_signal_handler;

/*
 * NCO - numerical controlled oscillator
 *     freq - desired output frequency
 *     clk_in_freq - frequency of the driving clock
 */

template<const long freq, const long clk_in_freq, typename signal_out>
struct NCO {
  long phase_increment;
  long phase_accumulator;
  signal_out clk_out;

#ifdef DEBUG
  long counter; // optional for verifying frequency
#endif

  NCO() { 
    phase_increment = freq - clk_in_freq;
    phase_accumulator = 0;

#ifdef DEBUG
    counter = 0;
#endif
  }
  
  void rising_edge(void) {
    phase_accumulator = phase_accumulator + phase_increment;
    if( phase_accumulator < 0 ) {
      phase_accumulator = phase_accumulator + clk_in_freq;
    }
    else {
      clk_out.toggle();

#ifdef DEBUG
      counter++;
#endif
    }
  }
};

/*
 * spew something on signal toggle
 */
template<const int sym_rising, const int sym_falling>
struct signal_print_ {
  unsigned x;

  signal_print_() : x(0) {}

  void toggle(void) {
    x = x ^ 1;
    putchar(((x) ? sym_rising : sym_falling ));
  }

};

/*
 * clock in tick / 
 * clk_80_Hz     + -
 * clk_160Hz     1 0
 */
int main(void)
{
  NCO<80,  clk_in_freq, signal_print_<'+','-'> > clk_freq1;
  NCO<160, clk_in_freq, signal_print_<'1','0'> > clk_freq2;

  for(long x=0; x < (clk_in_freq);++x) {

#ifdef DEBUG
    putchar((x&1)?'\\':'/');
#endif

    clk_freq1.rising_edge();
    clk_freq2.rising_edge();
  }
  
#ifdef DEBUG
  putchar('\n');
  printf("clk_freq1.counter=%ld\n", clk_freq1.counter);
  printf("clk_freq2.counter=%ld\n", clk_freq2.counter);
#endif

  return 0;
}

#if EXPECTED_OUTPUT
$ ./nco
/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0/\/\/\/1\/\/\/+0\/\/\/1\/\/\/-0\/\/\/\1/\/\/\+0/\/\/\1/\/\/\-0
clk_freq1.counter=80
clk_freq2.counter=160
#endif
  

nco.h

/* vim: set ts=2 sw=2 expandtab */

/*
 * File: nco.h - numerical control with arbritrary tick handler
 * Description: create an arbitrary frequency from a higher clock signal
 * Author: rick kimball
 * Date: 10/18/2017
 */

#ifndef NCO_H
#define NCO_H
/*
 * NCO - numerical controlled oscillator
 *     freq - desired output frequency
 *     clk_in_freq - frequency of the driving clock
 *     signal_out  - expects a structure or class with a void tick() 
 *                   function that is called once for each clock tick
 *                   of freq.
 */

template<const long freq, const long clk_in_freq, typename signal_out>
struct NCO {
  long phase_increment;
  long phase_accumulator;
  signal_out clk_out;

  /*
   * NCO ctor
   */
  NCO():
    phase_increment(freq - clk_in_freq)
    ,phase_accumulator(0) {
  }

  /* 
   *  rising_edge - compute new accumulator value and conditional trigger tick
   */
  void rising_edge(void) {
    phase_accumulator = phase_accumulator + phase_increment;
    if ( phase_accumulator < 0 ) {
      phase_accumulator = phase_accumulator + clk_in_freq;
    }
    else {
      clk_out.tick();
    }
  }
};


/*
 * default_signal_handler - minimum signal_out functions for NCO
 * 
 * void tick() - called each time frequency out clock tick is reached
 */
typedef struct {
  void tick(void) { }  /* called by NCO each tick of our oscillator */
} default_signal_handler;

#endif

sketch_oct17a

/*
 * arduino uno NCO sample sketch
 *  
 *  toggle 2 pins at different rates 10Hz and 3Hz
 */
#include "nco.h"

/*
 * our tick handler that toggles a pin
 * implemented as a c++ template to make it 
 * easy to create custom
 */
template<const unsigned pin_mask>
struct signal_toggleb {
  void tick(void) {
    PORTB ^= pin_mask;
  }
};

typedef signal_toggleb<(1<<4)> pin12_handler; // convenience typedef

// two clocks at different frequencies
// multiple by 2 to allow us to toggle pin for a high period and a low period
NCO < 60*2, 1000, pin12_handler >          clk_freq1; // toggle PB4 60Hz using a 1000Hz
NCO < 10*2, 1000, signal_toggleb<(1<<5)> > clk_freq2;  // toggle PB5 10Hz aka D13 LED

void setup() {
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
}

void loop() {
  static unsigned long prev;
  unsigned long curr = millis();

  /* use the millis() tick as our 1000Hz clock input signal */
  if ( prev != curr) {
    // catch up for any lost ticks to prevent frequency drift
    do {
      // send a pulse in to each NCO 
      clk_freq1.rising_edge();
      clk_freq2.rising_edge();
      prev++;
    } while ( prev != curr);
  }
}