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gba: cycle-based bitmap and affine backgrounds (#1714)
The pixel accuracy setting will now emulate the sub-pixel timing behaviours for bitmap and affine backgrounds described in [fleroviux's PPU docs](https://github.com/nba-emu/hw-docs/blob/main/src/ppu/background.md). This PR also splits the PPU into two separate libco threads: one for rendering and one for raising IRQs and starting DMAs. This allows the CPU and PPU to be run more asynchronously, which helps mitigate the performance cost of finer-grained PPU emulation.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,89 @@ | ||
| #include <gba/gba.hpp> | ||
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| //The only PPU state the CPU needs on every cycle is raised IRQs and DMAs, | ||
| //which occur independently of the render process. | ||
| //Display exists to put these events on a separate thread, | ||
| //so the CPU and PPU can run out-of-order. | ||
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| //hdraw: 1006 cycles | ||
| //hblank: 226 cycles | ||
| //scanline: 1232 cycles | ||
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| //vdraw: 160 scanlines (197120 cycles) | ||
| //vblank: 68 scanlines ( 83776 cycles) | ||
| //frame: 228 scanlines (280896 cycles) | ||
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| namespace ares::GameBoyAdvance { | ||
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| Display display; | ||
| #include "io.cpp" | ||
| #include "serialization.cpp" | ||
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| auto Display::load(Node::Object parent) -> void { | ||
| node = parent->append<Node::Object>("Display"); | ||
| } | ||
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| auto Display::unload() -> void { | ||
| node.reset(); | ||
| } | ||
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| auto Display::step(u32 clocks) -> void { | ||
| Thread::step(clocks); | ||
| Thread::synchronize(cpu); | ||
| } | ||
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| auto Display::main() -> void { | ||
| cpu.keypad.run(); | ||
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| io.vblank = io.vcounter >= 160 && io.vcounter <= 226; | ||
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| step(1); | ||
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| io.vcoincidence = io.vcounter == io.vcompare; | ||
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| if(io.vcounter == 160) { | ||
| if(io.irqvblank) cpu.setInterruptFlag(CPU::Interrupt::VBlank); | ||
| } | ||
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| step(1); | ||
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| if(io.irqvcoincidence) { | ||
| if(io.vcoincidence) cpu.setInterruptFlag(CPU::Interrupt::VCoincidence); | ||
| } | ||
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| if(io.vcounter == 160) { | ||
| cpu.dmaVblank(); | ||
| } | ||
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| step(3); | ||
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| if(io.vcounter == 162) { | ||
| if(videoCapture) cpu.dma[3].enable = 0; | ||
| videoCapture = !videoCapture && cpu.dma[3].timingMode == 3 && cpu.dma[3].enable; | ||
| } | ||
| if(io.vcounter >= 2 && io.vcounter < 162 && videoCapture) cpu.dmaHDMA(); | ||
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| step(1002); | ||
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| io.hblank = 1; | ||
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| step(1); | ||
| if(io.irqhblank) cpu.setInterruptFlag(CPU::Interrupt::HBlank); | ||
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| step(1); | ||
| if(io.vcounter < 160) cpu.dmaHblank(); | ||
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| step(223); | ||
| io.hblank = 0; | ||
| if(++io.vcounter == 228) io.vcounter = 0; | ||
| } | ||
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| auto Display::power() -> void { | ||
| Thread::create(system.frequency(), {&Display::main, this}); | ||
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| for(u32 n = 0x004; n <= 0x007; n++) bus.io[n] = this; | ||
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| io = {}; | ||
| } | ||
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| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,34 @@ | ||
| struct Display : Thread, IO { | ||
| Node::Object node; | ||
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| auto load(Node::Object) -> void; | ||
| auto unload() -> void; | ||
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| auto step(u32 clocks) -> void; | ||
| auto main() -> void; | ||
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| auto power() -> void; | ||
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| //io.cpp | ||
| auto readIO(n32 address) -> n8; | ||
| auto writeIO(n32 address, n8 byte) -> void; | ||
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| //serialization.cpp | ||
| auto serialize(serializer&) -> void; | ||
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| struct IO { | ||
| n1 vblank; | ||
| n1 hblank; | ||
| n1 vcoincidence; | ||
| n1 irqvblank; | ||
| n1 irqhblank; | ||
| n1 irqvcoincidence; | ||
| n8 vcompare; | ||
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| n16 vcounter; | ||
| } io; | ||
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| n1 videoCapture = 0; | ||
| }; | ||
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| extern Display display; |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,40 @@ | ||
| auto Display::readIO(n32 address) -> n8 { | ||
| switch(address) { | ||
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| //DISPSTAT | ||
| case 0x0400'0004: return ( | ||
| io.vblank << 0 | ||
| | io.hblank << 1 | ||
| | io.vcoincidence << 2 | ||
| | io.irqvblank << 3 | ||
| | io.irqhblank << 4 | ||
| | io.irqvcoincidence << 5 | ||
| ); | ||
| case 0x0400'0005: return ( | ||
| io.vcompare | ||
| ); | ||
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| //VCOUNT | ||
| case 0x0400'0006: return io.vcounter.byte(0); | ||
| case 0x0400'0007: return io.vcounter.byte(1); | ||
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| } | ||
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| return cpu.openBus.get(Byte, address); | ||
| } | ||
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| auto Display::writeIO(n32 address, n8 data) -> void { | ||
| switch(address) { | ||
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| //DISPSTAT | ||
| case 0x0400'0004: | ||
| io.irqvblank = data.bit(3); | ||
| io.irqhblank = data.bit(4); | ||
| io.irqvcoincidence = data.bit(5); | ||
| return; | ||
| case 0x0400'0005: | ||
| io.vcompare = data; | ||
| return; | ||
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| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,12 @@ | ||
| auto Display::serialize(serializer& s) -> void { | ||
| s(io.vblank); | ||
| s(io.hblank); | ||
| s(io.vcoincidence); | ||
| s(io.irqvblank); | ||
| s(io.irqhblank); | ||
| s(io.irqvcoincidence); | ||
| s(io.vcompare); | ||
| s(io.vcounter); | ||
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| s(videoCapture); | ||
| } |
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