Merge branch 'feature/nmi'

src/app/js_powered_app.ts

@@ -158,7 +158,7 @@ export class JsApp extends App {
         this.jsNes.update()
         this.updateAudio()
 
-        for (let i = VBlank.START; i <= VBlank.END; ++i) {
+        for (let i = VBlank.NMI; i <= VBlank.END; ++i) {
           this.jsNes.setHcount(i)
         }
       }

src/nes/cpu/cpu.ts

@@ -65,6 +65,7 @@ export class Cpu {
   private carry: Bit = 0
 
   private pc: Address  // Program counter
+  private nmiRequest = -1
   private irqRequest = 0
   private stallCycles = 0
 
@@ -128,17 +129,8 @@ export class Cpu {
   }
 
   // Non-maskable interrupt
-  public nmi(): void {
-    const vector = this.read16(VEC_NMI)
-    if (this.breakPoints.has(BreakType.NMI)) {
-      this.paused = true
-      console.warn(`paused because NMI: ${Util.hex(this.pc, 4)}, ${Util.hex(vector, 4)}`)
-    }
-
-    this.push16(this.pc)
-    this.push(this.getStatusReg() & ~BREAK_FLAG)
-    this.pc = vector
-    this.irqBlocked = 1
+  public requestNmi(): void {
+    this.nmiRequest = 2  // TODO: confirm.
   }
 
   public requestIrq(type: IrqType): void {
@@ -154,6 +146,21 @@ export class Cpu {
   }
 
   public step(): number {
+    if (this.nmiRequest >= 0) {
+      if (--this.nmiRequest < 0) {
+        const vector = this.read16(VEC_NMI)
+        this.push16(this.pc)
+        this.push(this.getStatusReg() & ~BREAK_FLAG)
+        this.pc = vector
+        this.irqBlocked = 1
+
+        if (this.breakPoints.has(BreakType.NMI)) {
+          this.paused = true
+          console.warn(`paused because NMI: ${Util.hex(this.pc, 4)}, ${Util.hex(vector, 4)}`)
+          return 0
+        }
+      }
+    }
     if (this.irqRequest !== 0 && this.irqBlocked === 0) {
       this.irqRequest = 0
       this.handleIrq()

src/nes/mapper/mapper005.ts

@@ -124,7 +124,7 @@ export class Mapper005 extends Mapper {
     // Note: BGs OR sprites MUST be enabled in $2001 (bits 3 and 4)
     // in order for the countdown to occur.
     const regs = this.options.getPpuRegs()
-    this.ppuInFrame = hcount < VBlank.START && (regs[PpuReg.MASK] & (PpuMaskBit.SHOW_SPRITE | PpuMaskBit.SHOW_BG)) !== 0
+    this.ppuInFrame = hcount < VBlank.NMI && (regs[PpuReg.MASK] & (PpuMaskBit.SHOW_SPRITE | PpuMaskBit.SHOW_BG)) !== 0
     if (this.ppuInFrame && this.irqHlineEnable && this.irqHlineCompare === hcount && hcount !== 0) {
       this.options.requestIrq(IrqType.EXTERNAL)
     }

src/nes/nes.ts

@@ -60,7 +60,7 @@ export class Nes {
   constructor(opt?: NesOption) {
     this.bus = new Bus()
     this.cpu = new Cpu(this.bus)
-    this.ppu = new Ppu(opt?.nmiFn || this.cpu.nmi.bind(this.cpu))
+    this.ppu = new Ppu(opt?.nmiFn || this.cpu.requestNmi.bind(this.cpu))
     this.apu = new Apu(this.gamePads, opt?.apuIrqFn || (() => this.cpu.requestIrq(IrqType.APU)))
     this.eventCallback = (_e, _p) => {}
     this.breakPointCallback = () => {}
@@ -301,7 +301,7 @@ export class Nes {
       this.apu.onHblank(hcount)
       this.mapper.onHblank(hcount)
 
-      if (hcount === VBlank.START)
+      if (hcount === VBlank.NMI)
         this.eventCallback(NesEvent.VBlank, (leftCycles / VCYCLE) | 0)
     }
     this.cycleCount = nextCycleCount

src/nes/ppu/ppu.ts

@@ -285,6 +285,7 @@ export class Ppu {
       value &= ~(PpuStatusBit.VBLANK | PpuStatusBit.SPRITE0HIT | PpuStatusBit.SPRITE_OVERFLOW)
     }
 
+    const before = this.regs[reg]
     this.regs[reg] = value
 
     switch (reg as PpuReg) {
@@ -295,6 +296,11 @@ export class Ppu {
         this.ppuAddr = ((this.ppuAddr & ~0x0c00) |
                         ((value & PpuCtrlBit.BASE_NAMETABLE_ADDRESS) << 10))
         this.updateCoarseX()
+
+        if ((value  & PpuCtrlBit.VINT_ENABLE) !== 0 &&
+            (before & PpuCtrlBit.VINT_ENABLE) === 0 &&
+            (this.regs[PpuReg.STATUS] & PpuStatusBit.VBLANK))
+          this.triggerNmi()
       }
       break
     case PpuReg.MASK:
@@ -373,11 +379,20 @@ export class Ppu {
     this.checkSprite0Hit(hcount)
 
     switch (hcount) {
-    case VBlank.START:
-      this.setVBlank()
-      break
+    // case VBlank.START:
+    // > Post-render scanline
+    // > The PPU just idles during this scanline. Even though accessing PPU memory
+    // > from the program would be safe here, the VBlank flag isn't set until after
+    // > this scanline.
+    //   break
     case VBlank.NMI:
-      if ((this.regs[PpuReg.CTRL] & PpuCtrlBit.VINT_ENABLE) !== 0)
+      // > Vertical blanking lines (241-260)
+      // > The VBlank flag of the PPU is set at tick 1 (the second tick) of scanline
+      // > 241, where the VBlank NMI also occurs. The PPU makes no memory accesses
+      // > during these scanlines, so PPU memory can be freely accessed by the program.
+      this.setVBlank()
+      if ((this.regs[PpuReg.CTRL] & PpuCtrlBit.VINT_ENABLE) !== 0 &&
+          (this.regs[PpuReg.STATUS] & PpuStatusBit.VBLANK) !== 0)
         this.triggerNmi()
       break
     case VBlank.END:

test/nes/cpu/cpu.spec.ts

@@ -33,7 +33,8 @@ describe('cpu', () => {
       0xfffd: 0xab,
     }))
     cpu.reset()
-    cpu.nmi()
+    cpu.requestNmi()
+    cpu.step()
     expect(cpu.getRegs().pc).toBe(0x9876)
   })