internal/{cpu,vm}: add memory to the vm, and refactor cpu/vm/memory code

README.md

@@ -4,4 +4,5 @@ Current references:
 - [6502 instruction set](https://www.masswerk.at/6502/6502_instruction_set.html)
 - [6502 memory test](http://www.willegal.net/appleii/6502mem.htm)
 - [6502 instructions description with undocumented commands](http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/64doc)
-- [a rust implementation](https://github.com/alexander-akhmetov/mos6502)
+- [a rust implementation](https://github.com/alexander-akhmetov/mos6502)
+- [MOS hardware manual](http://bytecollector.com/archive/misc/6500-10A_MCS6500hwMan_Jan76.pdf)

internal/cpu/cpu.go

@@ -1,5 +1,5 @@
-package cpu
+// Package cpu emulates a Mos6502 cpu
-
+//
 // A		....	Accumulator             OPC A           operand is AC (implied single byte instruction)
 // abs		....	absolute                OPC $LLHH       operand is address $HHLL *
 // abs,X	....	absolute, X-indexed     OPC $LLHH,X     operand is address; effective address is address incremented by X with carry **
@@ -13,9 +13,9 @@ package cpu
 // zpg		....	zeropage                OPC $LL         operand is zeropage address (hi-byte is zero, address = $00LL)
 // zpg,X	....	zeropage, X-indexed     OPC $LL,X       operand is zeropage address; effective address is address incremented by X without carry **
 // zpg,Y	....	zeropage, Y-indexed     OPC $LL,Y       operand is zeropage address; effective address is address incremented by Y without carry **
-
+//
 // 16-bit address words are little endian, lo(w)-byte first, followed by the hi(gh)-byte.
-
+//
 // SR Flags (bit 7 to bit 0):
 // N	....	Negative
 // V	....	Overflow
@@ -25,15 +25,16 @@ package cpu
 // I	....	Interrupt (IRQ disable)
 // Z	....	Zero
 // C	....	Carry
-
+//
 // Processor Stack:
 // LIFO, top down, 8 bit range, 0x0100 - 0x01FF
+package cpu
 
-// addressingMode is a type alias for a string, used below for defining addressing mode types
+// addrMode is a type alias for a string, used below for defining addressing modes
-type addressingMode int
+type addrMode int
 
 const (
-	accumulator addressingMode = iota
+	accumulator addrMode = iota
 	absolute
 	absoluteXIndexed
 	absoluteYIndexed
@@ -48,17 +49,39 @@ const (
 	zeroPageYIndexed
 )
 
+// Available cpu flags written as binary integer literals
+const (
+	flagDefault   uint8 = 0B_00110000
+	flagNegative  uint8 = 0B_10000000
+	flagOverflow  uint8 = 0B_01000000
+	flagB         uint8 = 0B_00010000
+	flagDecimal   uint8 = 0B_00001000
+	flagInterrupt uint8 = 0B_00000100
+	flagZero      uint8 = 0B_00000010
+	flagCarry     uint8 = 0B_00000001
+)
+
+// StackBottom represents the bottom address
+const StackBottom uint16 = 0x0100 // 256
+
 // Mos6502 TODO: docs
 type Mos6502 struct {
-	pc uint16 // program counter (16 bit)
+	sp uint8  // stack pointer
-	ac uint8  // accumulator (8 bit)
+	pc uint16 // program counter
-	x  uint8  // X register (8 bit)
+	a  uint8  // accumulator register
-	y  uint8  // Y register (8 bit)
+	x  uint8  // X index register
-	sr uint8  // status register [NV-BDIZC] (8 bit)
+	y  uint8  // Y index register
-	sp uint8  // stack pointer (8 bit)
+	p  uint8  // processor flags
 }
 
 // New TODO: docs
 func New() *Mos6502 {
-	return &Mos6502{}
+	return &Mos6502{
+		sp: 0xFF,
+		pc: 0,
+		a:  0,
+		x:  0,
+		y:  0,
+		p:  flagDefault,
+	}
 }

internal/cpu/opcodes.go

@@ -3,18 +3,18 @@ package cpu
 // op represents an operation. It includes the name of the op, it's 8 bit hexidecimal
 // opcode, how many bytes it occupies (it's size), as well as it's addressing mode.
 type op struct {
-	name           string
+	name     string
-	opcode         uint8
+	opcode   uint8
-	size           uint8
+	size     uint8
-	addressingMode addressingMode
+	addrMode addrMode
 }
 
-func newOp(name string, opcode, size uint8, addressingMode addressingMode) op {
+func newOp(name string, opcode, size uint8, addrMode addrMode) op {
 	return op{
-		name:           name,
+		name:     name,
-		opcode:         opcode,
+		opcode:   opcode,
-		size:           size,
+		size:     size,
-		addressingMode: addressingMode,
+		addrMode: addrMode,
 	}
 }
 

internal/vm/vm.go

@@ -0,0 +1,17 @@
+package vm
+
+import "github.com/bradford-hamilton/apple-1/internal/cpu"
+
+// Appleone represents the virtual Apple 1 computer
+type Appleone struct {
+	cpu *cpu.Mos6502    // virtual Mos6502 cpu
+	mem [64 * 1024]byte // available memory (64kiB)
+}
+
+// New returns a pointer to an initialized Appleone with a brand spankin new CPU
+func New() *Appleone {
+	return &Appleone{
+		cpu: cpu.New(),
+		mem: [64 * 1024]byte{},
+	}
+}

pkg/appleone/appleone.go

@@ -1,13 +0,0 @@
-package appleone
-
-import "github.com/bradford-hamilton/apple-1/internal/cpu"
-
-// Appleone represents our virtual Apple 1 computer
-type Appleone struct {
-	cpu *cpu.Mos6502
-}
-
-// New returns a pointer to an initialized Appleone with a brand spankin new CPU
-func New() *Appleone {
-	return &Appleone{cpu: cpu.New()}
-}