gba: add latches to DISPCNT background enable, object enable, and for…

…ce blank bits (#1643)

Clearing the force blank bit or setting the background/object enable
bits in DISPCNT should only take effect after 3 scanlines.

ares/gba/ppu/background.cpp

@@ -4,13 +4,19 @@ n1 PPU::Background::IO::frame;
 n5 PPU::Background::IO::mosaicWidth;
 n5 PPU::Background::IO::mosaicHeight;
 
+auto PPU::Background::setEnable(n1 status) -> void {
+  io.enable[3] = status;
+  for(auto& flag : io.enable) flag &= status;
+}
+
 auto PPU::Background::scanline(u32 y) -> void {
+  memory::move(io.enable, io.enable + 1, sizeof(io.enable) - 1);
   mosaicOffset = 0;
 }
 
 auto PPU::Background::run(u32 x, u32 y) -> void {
   output = {};
-  if(ppu.blank() || !io.enable) {
+  if(ppu.blank() || !io.enable[0]) {
     mosaic = {};
     return;
   }

ares/gba/ppu/io.cpp

@@ -8,17 +8,17 @@ auto PPU::readIO(n32 address) -> n8 {
   | Background::IO::frame << 4
   | objects.io.hblank     << 5
   | objects.io.mapping    << 6
-  | io.forceBlank         << 7
+  | io.forceBlank[3]      << 7
   );
   case 0x0400'0001: return (
-    bg0.io.enable     << 0
-  | bg1.io.enable     << 1
-  | bg2.io.enable     << 2
-  | bg3.io.enable     << 3
-  | objects.io.enable << 4
-  | window0.io.enable << 5
-  | window1.io.enable << 6
-  | window2.io.enable << 7
+    bg0.io.enable[3]     << 0
+  | bg1.io.enable[3]     << 1
+  | bg2.io.enable[3]     << 2
+  | bg3.io.enable[3]     << 3
+  | objects.io.enable[3] << 4
+  | window0.io.enable    << 5
+  | window1.io.enable    << 6
+  | window2.io.enable    << 7
   );
 
   //GRSWP
@@ -112,14 +112,15 @@ auto PPU::writeIO(n32 address, n8 data) -> void {
     Background::IO::frame = data.bit(4);
     objects.io.hblank     = data.bit(5);
     objects.io.mapping    = data.bit(6);
-    io.forceBlank         = data.bit(7);
+    io.forceBlank[3]      = data.bit(7);
+    for(auto& flag : io.forceBlank) flag |= data.bit(7);
     return;
   case 0x0400'0001:
-    bg0.io.enable     = data.bit(0);
-    bg1.io.enable     = data.bit(1);
-    bg2.io.enable     = data.bit(2);
-    bg3.io.enable     = data.bit(3);
-    objects.io.enable = data.bit(4);
+    bg0.setEnable(data.bit(0));
+    bg1.setEnable(data.bit(1));
+    bg2.setEnable(data.bit(2));
+    bg3.setEnable(data.bit(3));
+    objects.setEnable(data.bit(4));
     window0.io.enable = data.bit(5);
     window1.io.enable = data.bit(6);
     window2.io.enable = data.bit(7);

ares/gba/ppu/object.cpp

@@ -1,7 +1,15 @@
+auto PPU::Objects::setEnable(n1 status) -> void {
+  io.enable[3] = status;
+  for(auto& flag : io.enable) flag &= status;
+}
+
 auto PPU::Objects::scanline(u32 y) -> void {
+  memory::move(io.enable, io.enable + 1, sizeof(io.enable) - 1);
+  if(y >= 160) return;
+
   mosaicOffset = 0;
   for(auto& pixel : buffer) pixel = {};
-  if(ppu.blank() || !io.enable) return;
+  if(ppu.blank() || !io.enable[0]) return;
 
   for(auto& object : ppu.object) {
     n8 py = y - object.y;
@@ -74,7 +82,7 @@ auto PPU::Objects::scanline(u32 y) -> void {
 
 auto PPU::Objects::run(u32 x, u32 y) -> void {
   output = {};
-  if(ppu.blank() || !io.enable) {
+  if(ppu.blank() || !io.enable[0]) {
     mosaic = {};
     return;
   }

ares/gba/ppu/ppu.cpp

@@ -73,7 +73,7 @@ auto PPU::unload() -> void {
 }
 
 inline auto PPU::blank() -> bool {
-  return io.forceBlank || cpu.stopped();
+  return io.forceBlank[0] || cpu.stopped();
 }
 
 auto PPU::step(u32 clocks) -> void {
@@ -108,13 +108,14 @@ auto PPU::main() -> void {
 
   step(46);
 
-  if(io.vcounter < 160) {
-    u32 y = io.vcounter;
-    bg0.scanline(y);
-    bg1.scanline(y);
-    bg2.scanline(y);
-    bg3.scanline(y);
-    objects.scanline(y);
+  u32 y = io.vcounter;
+  memory::move(io.forceBlank, io.forceBlank + 1, sizeof(io.forceBlank) - 1);
+  bg0.scanline(y);
+  bg1.scanline(y);
+  bg2.scanline(y);
+  bg3.scanline(y);
+  objects.scanline(y);
+  if(y < 160) {
     auto line = screen->pixels().data() + y * 240;
     for(u32 x : range(240)) {
       bg0.run(x, y);

ares/gba/ppu/ppu.hpp

@@ -70,7 +70,7 @@ struct PPU : Thread, IO {
 
   struct IO {
     n1  gameBoyColorMode;
-    n1  forceBlank;
+    n1  forceBlank[4];
     n1  greenSwap;
 
     n1  vblank;
@@ -97,6 +97,7 @@ struct PPU : Thread, IO {
 
   struct Background {
     //background.cpp
+    auto setEnable(n1 status) -> void;
     auto scanline(u32 y) -> void;
     auto run(u32 x, u32 y) -> void;
     auto linear(u32 x, u32 y) -> void;
@@ -115,7 +116,7 @@ struct PPU : Thread, IO {
       static n5 mosaicWidth;
       static n5 mosaicHeight;
 
-      n1 enable;
+      n1 enable[4];
 
       n2 priority;
       n2 characterBase;
@@ -162,6 +163,7 @@ struct PPU : Thread, IO {
 
   struct Objects {
     //object.cpp
+    auto setEnable(n1 status) -> void;
     auto scanline(u32 y) -> void;
     auto run(u32 x, u32 y) -> void;
     auto power() -> void;
@@ -170,7 +172,7 @@ struct PPU : Thread, IO {
     auto serialize(serializer&) -> void;
 
     struct IO {
-      n1 enable;
+      n1 enable[4];
 
       n1 hblank;   //1 = allow access to OAM during Hblank
       n1 mapping;  //0 = two-dimensional, 1 = one-dimensional

ares/gba/ppu/serialization.cpp

@@ -5,7 +5,7 @@ auto PPU::serialize(serializer& s) -> void {
   s(pram);
 
   s(io.gameBoyColorMode);
-  s(io.forceBlank);
+  for(auto& flag : io.forceBlank) s(flag);
   s(io.greenSwap);
   s(io.vblank);
   s(io.hblank);
@@ -39,7 +39,7 @@ auto PPU::serialize(serializer& s) -> void {
 auto PPU::Background::serialize(serializer& s) -> void {
   s(id);
 
-  s(io.enable);
+  for(auto& flag : io.enable) s(flag);
   s(io.priority);
   s(io.characterBase);
   s(io.unused);
@@ -67,7 +67,7 @@ auto PPU::Background::serialize(serializer& s) -> void {
 }
 
 auto PPU::Objects::serialize(serializer& s) -> void {
-  s(io.enable);
+  for(auto& flag : io.enable) s(flag);
   s(io.hblank);
   s(io.mapping);
   s(io.mosaicWidth);

ares/gba/system/serialization.cpp

@@ -1,4 +1,4 @@
-static const string SerializerVersion = "v140";
+static const string SerializerVersion = "v140.1";
 
 auto System::serialize(bool synchronize) -> serializer {
   if(synchronize) scheduler.enter(Scheduler::Mode::Synchronize);