I'm very new to microprocessor programming so please bare with me.
I'm working on a research project at school. I need to generate different analog signals (the frequency can be hard coded) ranging from 1 HZ to 100 KHZ.
I found someones project on the internet and have tried to modify it to meet my needs. The biggest problems I have had have involved the timers.
In my code, a timer interrupt is set which increments a counter flag. In the loop, every time the counter flag is updated, parts of the signal are generated (using a DAC not PWM). At 1 HZ, the signal looks great. However, once I try and get up to 1KHZ, the signal is really ugly. If anyone could hint me in the right direction about how to fix it, that would be great.
Specifically, how can I disable PWM mode in the Timer2?
Thanks,
Chris
/*
*
* DDS Sine Generator mit ATMEGS 168
* Timer2 generates the 31250 KHz Clock Interrupt
*
* KHM 2009 / Martin Nawrath
* Kunsthochschule fuer Medien Koeln
* Academy of Media Arts Cologne
*/
#include "avr/pgmspace.h"
#include <avr/interrupt.h>
#include <avr/io.h>
#include <Wire.h>
byte Program = 64; // this sets the DAC register to receive new data
byte Device = 96; // This hardwired into the IC and the BoB, in other words, it is a given.
int sineVal = 0;
// table of 256 sine values / one sine period / stored in flash memory
PROGMEM prog_uchar sine256[] = {
127,130,133,136,139,143,146,149,152,155,158,161,164,167,170,173,176,178,181,184,187,190,192,195,198,200,203,205,208,210,212,215,217,219,221,223,225,227,229,231,233,234,236,238,239,240,
242,243,244,245,247,248,249,249,250,251,252,252,253,253,253,254,254,254,254,254,254,254,253,253,253,252,252,251,250,249,249,248,247,245,244,243,242,240,239,238,236,234,233,231,229,227,225,223,
221,219,217,215,212,210,208,205,203,200,198,195,192,190,187,184,181,178,176,173,170,167,164,161,158,155,152,149,146,143,139,136,133,130,127,124,121,118,115,111,108,105,102,99,96,93,90,87,84,81,78,
76,73,70,67,64,62,59,56,54,51,49,46,44,42,39,37,35,33,31,29,27,25,23,21,20,18,16,15,14,12,11,10,9,7,6,5,5,4,3,2,2,1,1,1,0,0,0,0,0,0,0,1,1,1,2,2,3,4,5,5,6,7,9,10,11,12,14,15,16,18,20,21,23,25,27,29,31,
33,35,37,39,42,44,46,49,51,54,56,59,62,64,67,70,73,76,78,81,84,87,90,93,96,99,102,105,108,111,115,118,121,124
};
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
double dfreq;
// const double refclk=31372.549; // =16MHz / 510
const double refclk=31376.6; // measured
// variables used inside interrupt service declared as voilatile
volatile byte icnt; // var inside interrupt
volatile unsigned long phaccu; // pahse accumulator
volatile unsigned long tword_m; // dds tuning word m
volatile int timerTick = 0;
void setup()
{
Wire.begin();
Serial.begin(115200); // connect to the serial port
Serial.println("DDS Test");
Setup_timer2();
// disable interrupts to avoid timing distortion
cbi (TIMSK0,TOIE0); // disable Timer0 !!! delay() is now not available
sbi (TIMSK2,TOIE2); // enable Timer2 Interrupt
dfreq=.5; // initial output frequency = 1000.o Hz
tword_m=pow(2,32)*dfreq/refclk; // calulate DDS new tuning word
}
void loop()
{
if (timerTick = 1)
{
Wire.beginTransmission(Device);
Wire.send(Program);
Wire.send(sineVal);
Wire.send(sineVal); // Needed twice, since the 4 lowest bits (of 12) are in the fourth byte
Wire.endTransmission();
Serial.print(sineVal);
Serial.print(", ");
timerTick = 0;
}
// if (c4ms > 250)
// { } // timer / wait fou a full second
}
//******************************************************************
// timer2 setup
// set prscaler to 1, PWM mode to phase correct PWM, 16000000/510 = 31372.55 Hz clock
void Setup_timer2() {
// Timer2 Clock Prescaler to : 1
sbi (TCCR2B, CS20);
cbi (TCCR2B, CS21);
cbi (TCCR2B, CS22);
// Timer2 PWM Mode set to Phase Correct PWM
cbi (TCCR2A, COM2A0); // clear Compare Match
cbi (TCCR2A, COM2A1);
cbi (TCCR2A, WGM20); // Mode 1 / Phase Correct PWM
cbi (TCCR2A, WGM21);
cbi (TCCR2B, WGM22);
}
//******************************************************************
// Timer2 Interrupt Service at 31372,550 KHz = 32uSec
// this is the timebase REFCLOCK for the DDS generator
// FOUT = (M (REFCLK)) / (2 exp 32)
// runtime : 8 microseconds ( inclusive push and pop)
// 125 ticks = 4 milliseconds
ISR(TIMER2_OVF_vect)
{
phaccu=phaccu+tword_m; // soft DDS, phase accu with 32 bits
icnt=phaccu >> 24; // use upper 8 bits for phase accu as frequency information
sineVal = pgm_read_byte_near(sine256 + icnt);
timerTick = 1;
}
