From 66b95576a9f0350b5cc269bb1ca76105d8e7d2c8 Mon Sep 17 00:00:00 2001
From: Mike Lynch <m.lynch@sydney.edu.au>
Date: Thu, 4 Jan 2024 11:19:09 +1100
Subject: [PATCH] Phased accumulator with a 32-bit waveform is kind of working

---
 waveforms/waveforms.ino | 55 +++++++++++------------------------------
 1 file changed, 15 insertions(+), 40 deletions(-)

diff --git a/waveforms/waveforms.ino b/waveforms/waveforms.ino
index 37b9bad..fb7e69f 100644
--- a/waveforms/waveforms.ino
+++ b/waveforms/waveforms.ino
@@ -7,7 +7,7 @@
 
 Adafruit_MCP4728 mcp;
 
-#define nsamp 256
+#define nsamp 32
 #define dacmax 256
 
 const byte nclk = 200; // a guess
@@ -16,45 +16,21 @@ long unsigned int phase;
 long unsigned int phase_inc;
 
 void setup() {
-
-//   // 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
+//  TIMSK0 &= ~_BV(TOIE0); // disable timer0 overflow interrupt
 
   Serial.begin(115200);
-  while (!Serial)
-    delay(10); // will pause Zero, Leonardo, etc until serial console opens
-
-
-  // Try to initialize!
 
   if (!mcp.begin(0x64)) {
-    Serial.println("Failed to find MCP4728 chip");
     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;
   calc_phase_inc();
 
@@ -63,6 +39,7 @@ void setup() {
 
 const float pi=3.14159265;
 byte waveform[nsamp];
+byte phaseb = 0;
 void setwave(){
   for (int isamp=0; isamp<nsamp; ++isamp){
     float phip=(isamp+0.5)/nsamp;
@@ -70,7 +47,7 @@ void setwave(){
     int val=0;
 
     //saw
-    //val = dacmax * isamp / nsamp;
+  //val = dacmax * isamp / nsamp;
     //val = ( isamp < nsamp / 2 ) ? 0 : dacmax - 1;
         //sine
     val=(sin(phi)+1.0)*dacmax/2;
@@ -85,19 +62,17 @@ void setwave(){
 
 //calculate the phase increment. 
 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() {
-  int redphase = phase >> 24;
+  phase += phase_inc;
+  int redphase = phase >> 27;
   mcp.fastWrite(waveform[redphase] << 4, 0, 0, 0);
-  //Serial.println(redphase);
 }