Add hack so zombie decrease kinda works

Following the technique described here: https://github.com/jkotlinski/apu-zombie-test, but looking for just these values in this order, without understanding any of the underlying behavior.
binji · Jun 6, 2023 · 6f0bf66 · 6f0bf66
1 parent b0ee86c
commit 6f0bf66
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diff --git a/src/emulator-debug.c b/src/emulator-debug.c
@@ -65,6 +65,8 @@ static int s_breakpoint_max_id;
   X(A, V, write_nrx2_initial_volume_abi, "(%#04x, %#02x) initial_volume=%u")   \
   X(A, V, write_nrx2_zombie_mode_abii,                                         \
     "(%#04x, %#02x) zombie mode: volume %u -> %u")                             \
+  X(A, V, write_nrx2_zombie_mode_hack_abi,                                     \
+    "(%#04x, %#02x) zombie mode hack: step %u")                                \
   X(A, D, write_nrx4_disable_channel_ab, "(%#04x, %#02x) disabling channel")   \
   X(A, D, write_nrx4_extra_length_clock_abi,                                   \
     "(%#04x, %#02x) extra length clock = %u")                                  \

diff --git a/src/emulator.c b/src/emulator.c
@@ -499,6 +499,7 @@ typedef struct {
   u8 volume;      /* 0..15 */
   u32 timer;      /* 0..period */
   Bool automatic; /* TRUE when MAX/MIN has not yet been reached. */
+  u8 zombie_step; /* HACK: support zombie volume decrease */
 } Envelope;
 
 /* Channel 1 and 2 */
@@ -2893,6 +2894,27 @@ static void write_nrx2_reg(Emulator* e, Channel* channel, Address addr,
       HOOK(write_nrx2_zombie_mode_abii, addr, value, channel->envelope.volume,
            new_volume);
       channel->envelope.volume = new_volume;
+      // Super ugly hack to support decreasing volume in zombie mode.
+      channel->envelope.zombie_step = value == 9;
+      if (value == 9) {
+        HOOK(write_nrx2_zombie_mode_hack_abi, addr, value,
+             channel->envelope.zombie_step);
+      }
+    } else if (UNLIKELY(channel->envelope.zombie_step > 0)) {
+      if (channel->envelope.zombie_step == 1 && value == 0x11) {
+        channel->envelope.zombie_step++;
+        HOOK(write_nrx2_zombie_mode_hack_abi, addr, value,
+             channel->envelope.zombie_step);
+      } else if (channel->envelope.zombie_step == 2 && value == 0x18) {
+        channel->envelope.zombie_step++;
+        u8 new_volume = (channel->envelope.volume + ENVELOPE_MAX_VOLUME - 1) &
+                        ENVELOPE_MAX_VOLUME;
+        HOOK(write_nrx2_zombie_mode_abii, addr, value, channel->envelope.volume,
+             new_volume);
+        channel->envelope.volume = new_volume;
+      } else {
+        channel->envelope.zombie_step = 0;
+      }
     }
   }
   channel->envelope.direction = UNPACK(value, NRX2_ENVELOPE_DIRECTION);