ym2612: fix timer behaviors

ares/component/audio/ym2612/io.cpp

@@ -36,18 +36,14 @@ auto YM2612::writeData(n8 data) -> void {
   //timer B period
   case 0x026: {
     timerB.period.bit(0,7) = data.bit(0,7);
+    // Not sure if this is the right place for it, but...
+    // handle a specific use case to reset the subticks on timer B
+    if(!timerB.enable) timerB.divider = 0;
     break;
   }
 
   //timer control
   case 0x027: {
-    //reload period on 0->1 transition
-    if(!timerA.enable && data.bit(0)) timerA.counter = timerA.period;
-    if(!timerB.enable && data.bit(1)) {
-      timerB.counter = timerB.period;
-      timerB.divider = 0;
-    }
-
     timerA.enable = data.bit(0);
     timerB.enable = data.bit(1);
     timerA.irq = data.bit(2);

ares/component/audio/ym2612/serialization.cpp

@@ -13,12 +13,14 @@ auto YM2612::serialize(serializer& s) -> void {
   s(envelope.divider);
 
   s(timerA.enable);
+  s(timerA.enableLatch);
   s(timerA.irq);
   s(timerA.line);
   s(timerA.period);
   s(timerA.counter);
 
   s(timerB.enable);
+  s(timerB.enableLatch);
   s(timerB.irq);
   s(timerB.line);
   s(timerB.period);

ares/component/audio/ym2612/timer.cpp

@@ -1,16 +1,15 @@
 auto YM2612::TimerA::run() -> void {
-  if(!enable) return;
-  if(++counter) return;
-
-  counter = period;
-  line |= irq;
+  if(!++counter)
+    line |= irq & enableLatch;
+  if(enableLatch < enable || !counter)
+    counter = period;
+  enableLatch = enable;
 }
 
 auto YM2612::TimerB::run() -> void {
-  if(!enable) return;
-  if(++divider) return;
-  if(++counter) return;
-
-  counter = period;
-  line |= irq;
+  if(!++divider && !++counter)
+    line |= irq & enableLatch;
+  if(enableLatch < enable || !counter && !divider)
+    counter = period; // do not reset divider on reenable
+  enableLatch = enable;
 }

ares/component/audio/ym2612/ym2612.hpp

@@ -45,6 +45,7 @@ struct YM2612 {
     auto run() -> void;
 
     n1  enable = 0;
+    n1  enableLatch = 0;
     n1  irq = 0;
     n1  line = 0;
     n10 period = 0;
@@ -56,6 +57,7 @@ struct YM2612 {
     auto run() -> void;
 
     n1 enable = 0;
+    n1 enableLatch = 0;
     n1 irq = 0;
     n1 line = 0;
     n8 period = 0;

ares/md/system/serialization.cpp

@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v142";
+static const string SerializerVersion = "v142.1";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);