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Phased accumulator with a 32-bit waveform is kind of working

main
Mike Lynch 2024-01-04 11:19:09 +11:00
parent 5c8e20e17d
commit 66b95576a9
1 changed files with 15 additions and 40 deletions
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55
waveforms/waveforms.ino
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@ -7,7 +7,7 @@
Adafruit_MCP4728 mcp; Adafruit_MCP4728 mcp;
#define nsamp 256 #define nsamp 32
#define dacmax 256 #define dacmax 256
const byte nclk = 200; // a guess const byte nclk = 200; // a guess
@ -16,45 +16,21 @@ long unsigned int phase;
long unsigned int phase_inc; long unsigned int phase_inc;
void setup() { void setup() {
// TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt
// // Set a timer interrupt for the phase accumulation
cli();//stop interrupts
//set timer1 interrupt at 44Hz
TCCR1A = 0;// set entire TCCR1A register to 0
TCCR1B = 0;// same for TCCR1B
TCNT1 = 0;//initialize counter value to 0
// set compare match register for 1hz increments
OCR1A = 500; // = (16 * 10**6) / (44000) - 1
// turn on CTC mode
TCCR1B |= (1 << WGM12);
// Set CS10 and CS12 bits for 1024 prescaler
TCCR1B |= (1 << CS12) | (1 << CS10);
// enable timer compare interrupt
TIMSK1 |= (1 << OCIE1A);
sei();//allow interrupts
Serial.begin(115200); Serial.begin(115200);
while (!Serial)
delay(10); // will pause Zero, Leonardo, etc until serial console opens
// Try to initialize!
if (!mcp.begin(0x64)) { if (!mcp.begin(0x64)) {
Serial.println("Failed to find MCP4728 chip");
while (1) { while (1) {
delay(10); delay(100);
} }
} else {
Serial.println("Adafruit MCP4728 initialised");
} }
Wire.setClock(3400000L); // mcp.setSpeed(400000L);
// mcp.setSpeed(800000L);
mcp.setSpeed(800000L);
freq=6600000; freq=440;
phase=0; phase=0;
calc_phase_inc(); calc_phase_inc();
@ -63,6 +39,7 @@ void setup() {
const float pi=3.14159265; const float pi=3.14159265;
byte waveform[nsamp]; byte waveform[nsamp];
byte phaseb = 0;
void setwave(){ void setwave(){
for (int isamp=0; isamp<nsamp; ++isamp){ for (int isamp=0; isamp<nsamp; ++isamp){
float phip=(isamp+0.5)/nsamp; float phip=(isamp+0.5)/nsamp;
@ -70,7 +47,7 @@ void setwave(){
int val=0; int val=0;
//saw //saw
//val = dacmax * isamp / nsamp; //val = dacmax * isamp / nsamp;
//val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1; //val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1;
//sine //sine
val=(sin(phi)+1.0)*dacmax/2; val=(sin(phi)+1.0)*dacmax/2;
@ -85,19 +62,17 @@ void setwave(){
//calculate the phase increment. //calculate the phase increment.
void calc_phase_inc(){ void calc_phase_inc(){
phase_inc=0.268435456*nclk*freq; // by measurement, 2^27 is about 138Hz (C below middle C)
// 2^27 / 138 = 972592.231884058
phase_inc = freq * 975592.231884058;
Serial.println(phase_inc);
} }
ISR(TIMER1_COMPA_vect){// timer1 interrupt
phase += phase_inc;
}
//regular running:
void loop() { void loop() {
int redphase = phase >> 24; phase += phase_inc;
int redphase = phase >> 27;
mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0); mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0);
//Serial.println(redphase);
} }