Make CPU stall on DMA

tyfkda · Mar 8, 2024 · 9bf4ba5 · 9bf4ba5
1 parent c1de200
commit 9bf4ba5
Show file tree

Hide file tree

Showing 3 changed files with 49 additions and 23 deletions.
diff --git a/src/nes/cpu/cpu.ts b/src/nes/cpu/cpu.ts
@@ -66,6 +66,7 @@ export class Cpu {
 
   private pc: Address  // Program counter
   private irqRequest = 0
+  private stallCycles = 0
 
   // For debug
   private breakPoints = new Set<Address | BreakType>()
@@ -148,6 +149,10 @@ export class Cpu {
     this.irqRequest &= ~(1 << type)
   }
 
+  public stall(cycles: number): void {
+    this.stallCycles = cycles
+  }
+
   public step(): number {
     if (this.irqRequest !== 0 && this.irqBlocked === 0) {
       this.irqRequest = 0
@@ -156,6 +161,12 @@ export class Cpu {
         return 0
     }
 
+    if (this.stallCycles > 0) {
+      const cycles = this.stallCycles
+      this.stallCycles = 0
+      return cycles
+    }
+
     let pc = this.pc
     const op = this.read8(pc++)
     const inst = kInstTable[op]

diff --git a/src/nes/mapper/mapper023.ts b/src/nes/mapper/mapper023.ts
@@ -79,41 +79,55 @@ class Mapper023Base extends Mapper {
       if (0xc000 <= adr && adr <= 0xefff) {  // CHR Select 2...7
         const reg = mapping[adr & 0xff]
         let ofs = 0, hi = false
-        if (reg === 0) {
+        switch (reg) {
+        case 0:
           ofs = 0
-        } else if (reg === 2) {
+          break
+        case 2:
           ofs = 0
           hi = true
-        } else if (reg === 4) {
+          break
+        case 4:
           ofs = 1
-        } else if (reg === 6) {
+          break
+        case 6:
           ofs = 1
           hi = true
-        } else {
+          break
+        default:
           return
         }
         const bank = ((adr & 0x3000) >> 11) + 2 + ofs
-        let newValue
+        let newValue: number
         if (hi)
           newValue = (this.chrBank[bank] & ~0x1f0) | ((value & 0x1f) << 4)
         else
           newValue = (this.chrBank[bank] & ~0x0f) | (value & 0x0f)
         this.setChrBankOffset(bank, newValue)
       } else {  // IRQ
         const reg = mapping[adr & 0xff]
-        if (reg === 0) {  // IRQ Latch: low 4 bits
+        switch (reg) {
+        case 0:  // IRQ Latch: low 4 bits
           this.irqLatch = (this.irqLatch & ~0x0f) | (value & 0x0f)
-        } else if (reg === 2) {  // IRQ Latch: high 4 bits
+          break
+        case 2:  // IRQ Latch: high 4 bits
           this.irqLatch = (this.irqLatch & ~0xf0) | ((value & 0x0f) << 4)
-        } else if (reg === 4) {  // IRQ Control
+          break
+        case 4:  // IRQ Control
           this.irqControl = value
           if ((this.irqControl & IRQ_ENABLE) !== 0) {
             this.irqCounter = this.irqLatch
           }
-        } else if (reg === 6) {  // IRQ Acknowledge
+          this.options.clearIrqRequest(IrqType.EXTERNAL)
+          break
+        case 6:  // IRQ Acknowledge
           // Copy to enable
-          const ea = this.irqControl & IRQ_ENABLE_AFTER
-          this.irqControl = (this.irqControl & ~IRQ_ENABLE) | (ea << 1)
+          {
+            const ea = this.irqControl & IRQ_ENABLE_AFTER
+            this.irqControl = (this.irqControl & ~IRQ_ENABLE) | (ea << 1)
+            this.options.clearIrqRequest(IrqType.EXTERNAL)
+          }
+          break
         }
       }
     })
@@ -153,14 +167,14 @@ class Mapper023Base extends Mapper {
   public onHblank(_hcount: number): void {
     if ((this.irqControl & IRQ_ENABLE) !== 0) {
       let c = this.irqCounter
-      if ((this.irqControl & IRQ_MODE) === 0) {  // scanline mode
-        c += 1
-      } else {  // cycle mode
-        c += 185  // TODO: Calculate.
-      }
-      if (c > 255) {
-        c = this.irqLatch
+      if (c >= 255) {
+        c += this.irqLatch - 255
         this.options.requestIrq(IrqType.EXTERNAL)
+      } else {
+        if ((this.irqControl & IRQ_MODE) === 0)  // scanline mode
+          c += 1
+        else  // cycle mode
+          c += 114  // 341 / 3
       }
       this.irqCounter = c
     }

diff --git a/src/nes/nes.ts b/src/nes/nes.ts
@@ -224,11 +224,13 @@ export class Nes {
     case OAMDMA:
       if (0 <= value && value <= 0x1f) {  // RAM
         this.ppu.copyWithDma(this.ram, value << 8)
-        // TODO: Consume CPU or GPU cycles.
+        this.cpu.stall(513)
       } else if (0x60 <= value && value <= 0x7f) {
         const sram = this.mapper.getSram()
-        if (sram != null)
+        if (sram != null) {
           this.ppu.copyWithDma(sram, (value - 0x60) << 8)
+          this.cpu.stall(513)
+        }
       } else {
         console.error(`OAMDMA not implemented except for RAM: ${Util.hex(value, 2)}`)
       }
@@ -297,11 +299,10 @@ export class Nes {
 
       this.ppu.setHcount(hcount)
       this.apu.onHblank(hcount)
+      this.mapper.onHblank(hcount)
 
       if (hcount === VBlank.START)
         this.eventCallback(NesEvent.VBlank, (leftCycles / VCYCLE) | 0)
-
-      this.mapper.onHblank(hcount)
     }
     this.cycleCount = nextCycleCount
   }