got rom to load

.gitignore

@@ -6,3 +6,5 @@ DerivedData/
 .swiftpm/configuration/registries.json
 .swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
 .netrc
+
+*.nes

Sources/Bus.swift

@@ -1,9 +1,17 @@
 class Bus {
     var cpuVram: [UInt8] = .init(repeating: 0, count: 2048)
+    var rom: Rom
+
     fileprivate let RAM : UInt16 = 0x0000
     fileprivate let RAM_MIRRORS_END: UInt16 = 0x1FFF
     fileprivate let PPU_REGISTERS: UInt16 = 0x2000
     fileprivate let PPU_REGISTERS_MIRRORS_END: UInt16 = 0x3FFF
+    fileprivate let ROM_ADDRESS_START: UInt16 = 0x8000
+    fileprivate let ROM_ADDRESS_END: UInt16 = 0xFFFF
+
+    init(_ rom: Rom) {
+        self.rom = rom
+    }
 }
 
 
@@ -16,6 +24,8 @@ extension Bus: Memory {
         case PPU_REGISTERS...PPU_REGISTERS_MIRRORS_END:
             let mirrorDownAddr = addr & 0b00100000_00000111;
             fatalError("PPU not implemented yet")
+        case ROM_ADDRESS_START...ROM_ADDRESS_END:
+            return readProgramRom(addr)
         default:
             print("Ignoring mem access at \(addr)")
             return 0
@@ -34,4 +44,13 @@ extension Bus: Memory {
             print("Ignorming mem-write at \(addr)")
         }
     }
+
+    func readProgramRom(_ addr: UInt16) -> UInt8 {
+        var addr = addr - 0x8000
+        if rom.program.count == 0x4000 && addr >= 0x4000 {
+            // rom mirroring
+            addr = addr % 0x4000
+        }
+        return rom.program[Int(addr)]
+    }
 }

Sources/CPU.swift

@@ -37,7 +37,7 @@ class CPU {
     var stackPointer: UInt8 = STACK_RESET
     var status: CPUFlags = [.interruptDisable, .break2]
     var programCounter: UInt16 = 0
-    var bus = Bus()
+    var bus: Bus?
 
 
     func getOpperandAddress(_ mode: AddressingMode) -> UInt16 {
@@ -99,6 +99,7 @@ class CPU {
 
     func load(_ program: [UInt8]) {
         //memory[0x0600 ..< (0x0600 + program.count)] = program[0..<program.count]
+        bus = Bus(try! Rom(program))
         memWriteU16(0xFFFC, data: 0x0600)
     }
 
@@ -390,19 +391,19 @@ class CPU {
 
 extension CPU: Memory {
     func memRead(_ addr: UInt16) -> UInt8 {
-        return bus.memRead(addr)
+        return bus!.memRead(addr)
     }
 
     func memWrite(_ addr: UInt16, data: UInt8) {
-        bus.memWrite(addr, data: data)
+        bus!.memWrite(addr, data: data)
     }
 
     func memReadU16(_ addr: UInt16) -> UInt16 {
-        return bus.memReadU16(addr)
+        return bus!.memReadU16(addr)
     }
 
     func memWriteU16(_ addr: UInt16, data: UInt16) {
-        bus.memWriteU16(addr, data: data)
+        bus!.memWriteU16(addr, data: data)
     }
 }
 

Sources/Rom.swift

@@ -8,7 +8,7 @@ struct Rom {
     var screenMirror: Mirroring
 
     init(_ raw: [UInt8]) throws {
-        guard raw[0...4] == [0x4E, 0x45, 0x53, 0x1A] else { throw HeaderParseError.notINES("File is not in iNES file format.") }
+        guard raw[0..<4] == [0x4E, 0x45, 0x53, 0x1A] else { throw HeaderParseError.notINES("File is not in iNES file format.") }
         mapper = (raw[7] & 0b1111_0000) | (raw[6] >> 4)
 
         let inesVer = (raw[7] >> 2) & 0b11
@@ -33,8 +33,8 @@ struct Rom {
         let programStart = 16 + (skipTrainer ? 512 : 0)
         let characterStart = programStart + programSize
 
-        program = Array(raw[programStart...(programStart + programSize)])
+        program = Array(raw[programStart..<(programStart + programSize)])
-        character = Array(raw[characterStart...(characterStart + characterSize)])
+        character = Array(raw[characterStart..<(characterStart + characterSize)])
     }
 }
 

Sources/main.swift

@@ -94,28 +94,10 @@ func readScreenState(_ cpu: CPU, frame: inout [UInt8]) -> Bool {
     return update
 }
 
-let gameCode: [UInt8] = [
+guard let rom = NSData(contentsOfFile: "snake.nes") else { fatalError("Rom not found") }
-    0x20, 0x06, 0x06, 0x20, 0x38, 0x06, 0x20, 0x0d, 0x06, 0x20, 0x2a, 0x06, 0x60, 0xa9, 0x02, 0x85,
+var gameCode = [UInt8](repeating: 0, count: rom.length)
-    0x02, 0xa9, 0x04, 0x85, 0x03, 0xa9, 0x11, 0x85, 0x10, 0xa9, 0x10, 0x85, 0x12, 0xa9, 0x0f, 0x85,
+rom.getBytes(&gameCode, length: rom.length)
-    0x14, 0xa9, 0x04, 0x85, 0x11, 0x85, 0x13, 0x85, 0x15, 0x60, 0xa5, 0xfe, 0x85, 0x00, 0xa5, 0xfe,
+
-    0x29, 0x03, 0x18, 0x69, 0x02, 0x85, 0x01, 0x60, 0x20, 0x4d, 0x06, 0x20, 0x8d, 0x06, 0x20, 0xc3,
-    0x06, 0x20, 0x19, 0x07, 0x20, 0x20, 0x07, 0x20, 0x2d, 0x07, 0x4c, 0x38, 0x06, 0xa5, 0xff, 0xc9,
-    0x77, 0xf0, 0x0d, 0xc9, 0x64, 0xf0, 0x14, 0xc9, 0x73, 0xf0, 0x1b, 0xc9, 0x61, 0xf0, 0x22, 0x60,
-    0xa9, 0x04, 0x24, 0x02, 0xd0, 0x26, 0xa9, 0x01, 0x85, 0x02, 0x60, 0xa9, 0x08, 0x24, 0x02, 0xd0,
-    0x1b, 0xa9, 0x02, 0x85, 0x02, 0x60, 0xa9, 0x01, 0x24, 0x02, 0xd0, 0x10, 0xa9, 0x04, 0x85, 0x02,
-    0x60, 0xa9, 0x02, 0x24, 0x02, 0xd0, 0x05, 0xa9, 0x08, 0x85, 0x02, 0x60, 0x60, 0x20, 0x94, 0x06,
-    0x20, 0xa8, 0x06, 0x60, 0xa5, 0x00, 0xc5, 0x10, 0xd0, 0x0d, 0xa5, 0x01, 0xc5, 0x11, 0xd0, 0x07,
-    0xe6, 0x03, 0xe6, 0x03, 0x20, 0x2a, 0x06, 0x60, 0xa2, 0x02, 0xb5, 0x10, 0xc5, 0x10, 0xd0, 0x06,
-    0xb5, 0x11, 0xc5, 0x11, 0xf0, 0x09, 0xe8, 0xe8, 0xe4, 0x03, 0xf0, 0x06, 0x4c, 0xaa, 0x06, 0x4c,
-    0x35, 0x07, 0x60, 0xa6, 0x03, 0xca, 0x8a, 0xb5, 0x10, 0x95, 0x12, 0xca, 0x10, 0xf9, 0xa5, 0x02,
-    0x4a, 0xb0, 0x09, 0x4a, 0xb0, 0x19, 0x4a, 0xb0, 0x1f, 0x4a, 0xb0, 0x2f, 0xa5, 0x10, 0x38, 0xe9,
-    0x20, 0x85, 0x10, 0x90, 0x01, 0x60, 0xc6, 0x11, 0xa9, 0x01, 0xc5, 0x11, 0xf0, 0x28, 0x60, 0xe6,
-    0x10, 0xa9, 0x1f, 0x24, 0x10, 0xf0, 0x1f, 0x60, 0xa5, 0x10, 0x18, 0x69, 0x20, 0x85, 0x10, 0xb0,
-    0x01, 0x60, 0xe6, 0x11, 0xa9, 0x06, 0xc5, 0x11, 0xf0, 0x0c, 0x60, 0xc6, 0x10, 0xa5, 0x10, 0x29,
-    0x1f, 0xc9, 0x1f, 0xf0, 0x01, 0x60, 0x4c, 0x35, 0x07, 0xa0, 0x00, 0xa5, 0xfe, 0x91, 0x00, 0x60,
-    0xa6, 0x03, 0xa9, 0x00, 0x81, 0x10, 0xa2, 0x00, 0xa9, 0x01, 0x81, 0x10, 0x60, 0xa2, 0x00, 0xea,
-    0xea, 0xca, 0xd0, 0xfb, 0x60
-]
 
 var cpu = CPU()
 cpu.load(gameCode)