Revision 23:7a9ff5230149, committed 2017-12-15

Comitter:

davolfman

Date:

Fri Dec 15 04:50:56 2017 +0000

Parent:

22:0307adac8c35

Commit message:

Integration of main comments and added FastSin comments.

Changed in this revision

--- a/main.cpp	Fri Dec 15 03:51:47 2017 +0000
+++ b/main.cpp	Fri Dec 15 04:50:56 2017 +0000
@@ -76,12 +76,20 @@
 int carS = 0;//carrier sustain level
 int carR = 0xffff;//carrier release level
 
+///@brief Converts a phase of period 2^16 into a sine value
+///@phase The phase to calculate the sine of in phase/65536 * 2 pi radians
+///@return the sine as a signed 16 bit fractonal part inside a 32 bit int
 int fastSin(const int phase){
+    //the middle 12 bits are used to index into a lookuptable of pre computed sines
     int index = (phase & 0x3ffc) >> 2;
+    
+    //we used linear interpolation given out bottom 2 bits to turn a 2^12 Look Up Table into a 2^14 LUT
     int subindex = phase & 0x3;
+    
+    //We use mirroring of a quarter wave of sine so we only have to store a quarter of the samples again
     int quadrant = (phase & 0xc000) >> 14;
     int sum = 0;
-    switch (quadrant) {
+    switch (quadrant) {//perform the mirroring and add the memebers of the weighted average for interpolation
         case 0:
             sum += (4 - subindex) * sinTable[index];
             sum += subindex * sinTable[index+1];
@@ -99,7 +107,8 @@
             sum -= subindex * sinTable[4095-index];
             break;
     }
-    sum = sum >> 2;
+    sum = sum >> 2;//divide the weighted sum of the neighborign samples by 4
+    //to get a weighted average
     
     return sum;
 }
@@ -211,77 +220,94 @@
     int64_t keytemp;
     int tempCarA, tempCarD, tempCarR, tempModA, tempModD, tempModR;
 
-    for(int i = 0; i < numKeys; ++i){
+    for(int i = 0; i < numKeys; ++i){ //zero out values
         carrierPhases[i] = 0;
         modulatorPhases[i] = 0;
         envelopeAmpsC[i] = 0;
         envelopeAmpsM[i] = 0;
     }
     
-    keyBank.mode(PullNone);
-    synthesisClock.attach(synthesize, 0.00005);
+    keyBank.mode(PullNone); // we're using external pullup resistors, 
+                //and things weren't working this didn't fix it but better safe
+                
+    synthesisClock.attach(synthesize, 0.00005); //this runs every 50 us or 20khz
     
     while(true){
-        ratNumer = 0xf & ~ numerator;
-        ratDenom = 0xf & ~ denominator;
-        FMmult = (ratNumer << 16) / ratDenom;
+        ratNumer = 0xf & ~ numerator; //read ratio numerator
+        ratDenom = 0xf & ~ denominator; //read ratio denominator
+        FMmult = (ratNumer << 16) / ratDenom; //FM multiplier = numerator / denominator
+        
+        Volume = (int)inVol.read_u16(); //read volume
         
-        Volume = (int)inVol.read_u16();
+        modVol = (int)inModAmt.read_u16(); //read modulation amount
         
-        modVol = (int)inModAmt.read_u16();
-        
+        //ensure we don't divide by zero on any of these
+
+        //read carrier attack
         tempCarA = inCarA.read_u16();
         if(! tempCarA)
             carA = 0xffff;
         else
             carA = 0xffff / tempCarA;
         
+        //read carrier decay
         tempCarD = inCarD.read_u16();
         if(! tempCarD)
             carD = 0xffff;
         else
             carD = 0xffff / tempCarD;
         
+        //read carrier sustain
         carS = (int)inCarS.read_u16();
         
+        //read carrier release
         tempCarR = inCarR.read_u16();
         if(! tempCarR)
             carR = 0xffff;
         else
             carR = 0xffff / tempCarR;
         
+        //read modulation attack
         tempModA = inModA.read_u16();
         if(! tempModA)
             modA = 0xffff;
         else
             modA = 0xffff / tempModA;
         
+        //read modulation decay
         tempModD = inModD.read_u16();
         if(! tempModD)
             modD = 0xffff;
         else
             modD = 0xffff / tempModD;
         
+        //read modulation sustain
         modS = (int)inModS.read_u16();
         
+        //read modulation release
         tempModR = inModR.read_u16();
         if(! tempModR)
             modR = 0xffff;
         else
             modR = 0xffff / tempModR;
         
-        keytemp = 0; //zero the keys before we start ORing on top of everything
-        for(int i = 0; i < 9; ++i) {
-            bankSelect = (~(1 << i)) & bankSelect.mask();
-            wait_us(200);
-            int shiftOffset = 6LL * i;
+        keytemp = 0; //zero the keys before we start ORing on top of everything, 
+        //keytemp is a buffer that waits until every key is read, then it pushes 
+        //into the 'keyboard' variable
+        
+        for(int i = 0; i < 9; ++i) {//for all 9 half-octaves of the keyboard
+            bankSelect = (~(1 << i)) & bankSelect.mask();//supply power (as ground) to that bank
+            wait_us(200); //delay to get to get full reading
+            int shiftOffset = 6LL * i; //read the keys in the bank
             
+            //assign the bank to its corresponding position in the overall keyboard
             keytemp |= ((~(unsigned long long)keyBank) & (unsigned long long)keyBank.mask()) << (unsigned long long)shiftOffset;
         }
-        keytemp >>= 5;
+        keytemp >>= 5;//shift 5 over because bank 0 only has 1 key and it is the 6th key (...111111 111111 100000)
         
-        keyboard = keytemp;
+        keyboard = keytemp;//push our read values once we are complete. 
+        //This only takes 1 cycle, especially since we are using 'keyboard' in the ISR
         
-        //wait_ms(10);
+        //wait_ms(10);//we've stopped bothering to wait here.  it didn't make a difference
     }
 }