From f03ed7c83310816802303fd6aef8836d50683181 Mon Sep 17 00:00:00 2001
From: tildearrow <tildearrow@protonmail.com>
Date: Tue, 1 Feb 2022 18:28:48 -0500
Subject: [PATCH] NES: add hardware sweep effect

---
 papers/doc/7-systems/nes.md |  8 ++++++++
 src/engine/dispatch.h       |  2 ++
 src/engine/platform/nes.cpp | 19 +++++++++++++++++--
 src/engine/platform/nes.h   |  2 +-
 src/engine/playback.cpp     |  8 ++++++++
 5 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/papers/doc/7-systems/nes.md b/papers/doc/7-systems/nes.md
index 6ca0d8b77..dc6eb20af 100644
--- a/papers/doc/7-systems/nes.md
+++ b/papers/doc/7-systems/nes.md
@@ -8,3 +8,11 @@ also known as Famicom.
 
 - `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.
+  - `x` is the time.
+  - `y` is the shift.
+  - set to 0 to disable it.
+- `14xy`: setup sweep down.
+  - `x` is the time.
+  - `y` is the shift.
+  - set to 0 to disable it.
\ No newline at end of file
diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index 0ddc6cd30..c9d49861d 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -53,6 +53,8 @@ enum DivDispatchCmds {
   DIV_CMD_PCE_LFO_MODE,
   DIV_CMD_PCE_LFO_SPEED,
 
+  DIV_CMD_NES_SWEEP,
+
   DIV_CMD_C64_CUTOFF,
   DIV_CMD_C64_RESONANCE,
   DIV_CMD_C64_FILTER_MODE,
diff --git a/src/engine/platform/nes.cpp b/src/engine/platform/nes.cpp
index 5527418a2..222d6b37d 100644
--- a/src/engine/platform/nes.cpp
+++ b/src/engine/platform/nes.cpp
@@ -300,6 +300,19 @@ int DivPlatformNES::dispatch(DivCommand c) {
         chan[c.chan].freqChanged=true;
       }
       break;
+    case DIV_CMD_NES_SWEEP:
+      if (c.chan>1) break;
+      if (c.value2==0) {
+        chan[c.chan].sweep=0x08;
+      } else {
+        if (!c.value) { // down
+          chan[c.chan].sweep=0x88|(c.value2&0x77);
+        } else { // up
+          chan[c.chan].sweep=0x80|(c.value2&0x77);
+        }
+      }
+      rWrite(0x4001+(c.chan*4),chan[c.chan].sweep);
+      break;
     case DIV_CMD_SAMPLE_BANK:
       sampleBank=c.value;
       if (sampleBank>(parent->song.sample.size()/12)) {
@@ -341,6 +354,8 @@ void DivPlatformNES::forceIns() {
     chan[i].insChanged=true;
     chan[i].prevFreq=65535;
   }
+  rWrite(0x4001,chan[0].sweep);
+  rWrite(0x4005,chan[1].sweep);
 }
 
 void* DivPlatformNES::getChanState(int ch) {
@@ -366,8 +381,8 @@ void DivPlatformNES::reset() {
   nes->apu.cpu_opcode_cycle=0;
 
   rWrite(0x4015,(!isMuted[0])|((!isMuted[1])<<1)|((!isMuted[2])<<2)|((!isMuted[3])<<3)|((!isMuted[4])<<4));
-  rWrite(0x4001,0x08);
-  rWrite(0x4005,0x08);
+  rWrite(0x4001,chan[0].sweep);
+  rWrite(0x4005,chan[1].sweep);
 }
 
 bool DivPlatformNES::keyOffAffectsArp(int ch) {
diff --git a/src/engine/platform/nes.h b/src/engine/platform/nes.h
index bb8b5adc8..edc130ae3 100644
--- a/src/engine/platform/nes.h
+++ b/src/engine/platform/nes.h
@@ -19,7 +19,7 @@ class DivPlatformNES: public DivDispatch {
       note(0),
       ins(-1),
       duty(0),
-      sweep(0),
+      sweep(8),
       active(false),
       insChanged(true),
       freqChanged(false),
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 2ba7a5036..80e9e14c9 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -65,6 +65,8 @@ const char* cmdName[DIV_CMD_MAX]={
   "PCE_LFO_MODE",
   "PCE_LFO_SPEED",
 
+  "NES_SWEEP",
+
   "C64_CUTOFF",
   "C64_RESONANCE",
   "C64_FILTER_MODE",
@@ -178,6 +180,12 @@ bool DivEngine::perSystemEffect(int ch, unsigned char effect, unsigned char effe
         case 0x12: // duty or noise mode
           dispatchCmd(DivCommand(DIV_CMD_STD_NOISE_MODE,ch,effectVal));
           break;
+        case 0x13: // sweep up
+          dispatchCmd(DivCommand(DIV_CMD_NES_SWEEP,ch,0,effectVal));
+          break;
+        case 0x14: // sweep down
+          dispatchCmd(DivCommand(DIV_CMD_NES_SWEEP,ch,1,effectVal));
+          break;
         default:
           return false;
       }