md: better handle 32X PWM sample/clock rate changes

Author: LukeUsher

ares/md/m32x/m32x.hpp

@@ -130,6 +130,7 @@ struct M32X {
     auto main() -> void;
     auto step(u32 clocks) -> void;
     auto power(bool reset) -> void;
+    auto updateFrequency() -> void;
 
     //serialization.cpp
     auto serialize(serializer&) -> void;

ares/md/m32x/pwm.cpp

@@ -1,7 +1,8 @@
 auto M32X::PWM::load(Node::Object parent) -> void {
   stream = parent->append<Node::Audio::Stream>("PWM");
   stream->setChannels(2);
-  stream->setFrequency(44'100);
+  n12 clocks = cycle - 1;
+  updateFrequency();
 }
 
 auto M32X::PWM::unload(Node::Object parent) -> void {
@@ -10,36 +11,41 @@ auto M32X::PWM::unload(Node::Object parent) -> void {
 }
 
 auto M32X::PWM::main() -> void {
-  n12 clocks = cycle-1;
-  if(clocks && (lmode.bit(0)^lmode.bit(1) || rmode.bit(0)^rmode.bit(1))) {
-    if(lmode == 1) lsample = lfifo.read();
-    if(lmode == 2) lsample = rfifo.read();
+    n12 clocks = cycle - 1;
 
-    if(rmode == 1) rsample = rfifo.read();
-    if(rmode == 2) rsample = lfifo.read();
+    //check if cycle rate has changed and update sample rate accordingly
+    static n12 previousCycle = cycle;
+    if (cycle != previousCycle) {
+      previousCycle = cycle;
+      updateFrequency();
+    }
+
+    if (clocks && (lmode.bit(0) ^ lmode.bit(1) || rmode.bit(0) ^ rmode.bit(1))) {
+        if (lmode == 1) lsample = lfifo.read();
+        if (lmode == 2) lsample = rfifo.read();
+
+        if (rmode == 1) rsample = rfifo.read();
+        if (rmode == 2) rsample = lfifo.read();
 
-    lfifoLatch.bit(14) = lfifo.empty();
-    rfifoLatch.bit(14) = rfifo.empty();
-    mfifoLatch.bit(14) = lfifoLatch.bit(14) & rfifoLatch.bit(14);
+        lfifoLatch.bit(14) = lfifo.empty();
+        rfifoLatch.bit(14) = rfifo.empty();
+        mfifoLatch.bit(14) = lfifoLatch.bit(14) & rfifoLatch.bit(14);
 
-    if(periods++ == n4(timer-1)) {
-      periods = 0;
-      m32x.shm.irq.pwm.active = 1;
-      m32x.shs.irq.pwm.active = 1;
-      m32x.shm.dmac.dreq[1] = dreqIRQ;
-      m32x.shs.dmac.dreq[1] = dreqIRQ;
+        if (periods++ == n4(timer - 1)) {
+            periods = 0;
+            m32x.shm.irq.pwm.active = 1;
+            m32x.shs.irq.pwm.active = 1;
+            m32x.shm.dmac.dreq[1] = dreqIRQ;
+            m32x.shs.dmac.dreq[1] = dreqIRQ;
+        }
     }
-  }
 
-  counter += max(1, clocks);
-  while(counter >= 522) {
-    counter -= 522;
     auto left = cycle > 0 ? lsample / (f32)cycle : 0;
     auto right = cycle > 0 ? rsample / (f32)cycle : 0;
-    stream->frame(left, right);
-  }
 
-  step(clocks);
+    stream->frame(left, right);  // Output the frame without the loop, since the sample rate is adjusted dynamically
+
+    step(clocks);
 }
 
 auto M32X::PWM::step(u32 clocks) -> void {
@@ -64,4 +70,10 @@ auto M32X::PWM::power(bool reset) -> void {
   lfifoLatch = 0x4000; // empty
   rfifoLatch = 0x4000; // empty
   mfifoLatch = 0x4000; // empty
+  updateFrequency();
+}
+
+auto M32X::PWM::updateFrequency() -> void {
+  n12 clocks = cycle - 1;
+  stream->setFrequency((system.frequency() * 6) / (7.0 * (2 * (clocks) - 1)));
 }