NES: add DMC write effect

papers/doc/7-systems/nes.md

@@ -2,10 +2,13 @@
 
 the console from Nintendo that plays Super Mario Bros. and helped revive the agonizing video game market in the US during mid-80s.
 
-also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and  fifth is a (D)PCM sample channel
+also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and fifth is a (D)PCM sample channel
 
 # effects
 
+- `11xx`: write to delta modulation counter.
+  - this may be used to attenuate the triangle and noise channels.
+  - will not work if a sample is playing.
 - `12xx`: set duty cycle or noise mode of channel.
   - may be 0-3 for the pulse channels and 0-1 for the noise channel.
 - `13xy`: setup sweep up.
@@ -15,4 +18,4 @@ also known as Famicom. It is a five-channel PSG: first two channels play pulse w
 - `14xy`: setup sweep down.
   - `x` is the time.
   - `y` is the shift.
-  - set to 0 to disable it.
+  - set to 0 to disable it.

src/engine/dispatch.h

@@ -86,6 +86,7 @@ enum DivDispatchCmds {
   DIV_CMD_PCE_LFO_SPEED, // (speed)
 
   DIV_CMD_NES_SWEEP, // (direction, value)
+  DIV_CMD_NES_DMC, // (value)
 
   DIV_CMD_C64_CUTOFF, // (value)
   DIV_CMD_C64_RESONANCE, // (value)

src/engine/platform/nes.cpp

@@ -59,6 +59,9 @@ const char** DivPlatformNES::getRegisterSheet() {
 
 const char* DivPlatformNES::getEffectName(unsigned char effect) {
   switch (effect) {
+    case 0x11:
+      return "Write to delta modulation counter (0 to 7F)";
+      break;
     case 0x12:
       return "12xx: Set duty cycle/noise mode (pulse: 0 to 3; noise: 0 or 1)";
       break;
@@ -420,6 +423,9 @@ int DivPlatformNES::dispatch(DivCommand c) {
       }
       rWrite(0x4001+(c.chan*4),chan[c.chan].sweep);
       break;
+    case DIV_CMD_NES_DMC:
+      rWrite(0x4011,c.value&0x7f);
+      break;
     case DIV_CMD_SAMPLE_BANK:
       sampleBank=c.value;
       if (sampleBank>(parent->song.sample.size()/12)) {

src/engine/playback.cpp

@@ -88,6 +88,7 @@ const char* cmdName[]={
   "PCE_LFO_SPEED",
 
   "NES_SWEEP",
+  "NES_DMC",
 
   "C64_CUTOFF",
   "C64_RESONANCE",
@@ -317,6 +318,9 @@ bool DivEngine::perSystemEffect(int ch, unsigned char effect, unsigned char effe
     case DIV_SYSTEM_NES:
     case DIV_SYSTEM_MMC5:
       switch (effect) {
+        case 0x11: // DMC write
+          dispatchCmd(DivCommand(DIV_CMD_NES_DMC,ch,effectVal));
+          break;
         case 0x12: // duty or noise mode
           dispatchCmd(DivCommand(DIV_CMD_STD_NOISE_MODE,ch,effectVal));
           break;