afsk.ino

#include <util/crc16.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#include <SPI.h>
#include <avr/pgmspace.h>
#include "ax25modem.h"

static const uint8_t PROGMEM _sine_table[] = {
#include "sine_table.h"
};

/* CONFIGURABLE BITS */

#define APRS_TX_INTERVAL  120000  // APRS TX Interval 
#define RADIO_POWER  0x07
/*
 0x02  5db (3mW)
 0x03  8db (6mW)
 0x04 11db (12mW)
 0x05 14db (25mW)
 0x06 17db (50mW)
 0x07 20db (100mW)
 */

#define HX1_ENABLE 5
#define HX1_TXD    9

#define BAUD_RATE      (1200)
#define TABLE_SIZE     (512)
#define PREAMBLE_BYTES (25)
#define REST_BYTES     (5)

#define PLAYBACK_RATE    (F_CPU / 256)
#define SAMPLES_PER_BAUD (PLAYBACK_RATE / BAUD_RATE)
#define PHASE_DELTA_1200 (((TABLE_SIZE * 1200L) << 7) / PLAYBACK_RATE)
#define PHASE_DELTA_2200 (((TABLE_SIZE * 2200L) << 7) / PLAYBACK_RATE)
#define PHASE_DELTA_XOR  (PHASE_DELTA_1200 ^ PHASE_DELTA_2200)

char txstring[80];  
volatile static uint8_t *_txbuf = 0;
volatile static uint8_t  _txlen = 0;
volatile int txstatus=1;
volatile int txstringlength=0;
volatile char txc;
volatile int txi;
volatile int txj;
volatile boolean lockvariables = 0;

_txbuf = "NORMAN PRICE\n"

void setup() {
  pinMode(HX1_ENABLE, OUTPUT);
  digitalWrite(HX1_ENABLE, LOW);
  wait(500);
  initialise_interrupt();


ISR(TIMER2_OVF_vect)
{
  static uint16_t phase  = 0;
  static uint16_t step   = PHASE_DELTA_1200;
  static uint16_t sample = 0;
  static uint8_t rest    = PREAMBLE_BYTES + REST_BYTES;
  static uint8_t byte;
  static uint8_t bit     = 7;
  static int8_t bc       = 0;

  /* Update the PWM output */
  OCR2B = pgm_read_byte(&_sine_table[(phase >> 7) & 0x1FF]);
  phase += step;

  if(++sample < SAMPLES_PER_BAUD) return;
  sample = 0;

  /* Zero-bit insertion */
  if(bc == 5)
  {
    step ^= PHASE_DELTA_XOR;
    bc = 0;
    return;
  }

  /* Load the next byte */
  if(++bit == 8)
  {
    bit = 0;

    if(rest > REST_BYTES || !_txlen)
    {
      if(!--rest)
      {
        /* Disable radio and interrupt */
        //PORTA &= ~TXENABLE;
        TIMSK2 &= ~_BV(TOIE2);

        /* Prepare state for next run */
        phase = sample = 0;
        step  = PHASE_DELTA_1200;
        rest  = PREAMBLE_BYTES + REST_BYTES;
        bit   = 7;
        bc    = 0;

        return;
      }

      /* Rest period, transmit ax.25 header */
      byte = 0x7E;
      bc = -1;
    }
    else
    {
      /* Read the next byte from memory */
      byte = *(_txbuf++);
      if(!--_txlen) rest = REST_BYTES + 2;
      if(bc < 0) bc = 0;
    }
  }

  /* Find the next bit */
  if(byte & 1)
  {
    /* 1: Output frequency stays the same */
    if(bc >= 0) bc++;
  }
  else
  {
    /* 0: Toggle the output frequency */
    step ^= PHASE_DELTA_XOR;
    if(bc >= 0) bc = 0;
  }

  byte >>= 1;
}