mirror of
https://github.com/bradford-hamilton/apple-1.git
synced 2024-06-02 12:41:27 +00:00
129 lines
2.7 KiB
Go
129 lines
2.7 KiB
Go
package vm
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import (
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"fmt"
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)
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// Appleone represents the virtual Apple 1 computer
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type Appleone struct {
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cpu *Mos6502 // virtual mos6502 cpu
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mem block // available memory (64kiB)
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}
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// New returns a pointer to an initialized Appleone with a brand spankin new CPU
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func New() *Appleone {
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return &Appleone{
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cpu: newCPU(),
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mem: newBlock(),
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}
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}
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func (a *Appleone) load(addr uint16, data []uint8) {
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a.mem.load(addr, data)
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a.cpu.pc = addr
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}
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func (a *Appleone) step() {
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op, err := opByCode(a.mem[a.cpu.pc])
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if err != nil {
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fmt.Println("TODO")
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}
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a.cpu.pc += uint16(op.size)
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if err := op.exec(a, op); err != nil {
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fmt.Println("TODO")
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}
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}
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func (a *Appleone) littleEndianToUint16(big, little uint8) uint16 {
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return uint16(a.mem[big])<<8 | uint16(a.mem[little])
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}
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// pushWordToStack pushes the given word (byte) into memory and sets the new stack pointer
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func (a *Appleone) pushWordToStack(b byte) {
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a.mem[StackBottom+uint16(a.cpu.sp)] = b
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a.cpu.sp = uint8((uint16(a.cpu.sp) - 1) & 0xFF)
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}
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// pushWordToStack splits the high and low byte of the data passed in, and pushes them to the stack
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func (a *Appleone) pushDWordToStack(data uint16) {
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h := uint8((data >> 8) & 0xFF)
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l := uint8(data & 0xFF)
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a.pushWordToStack(h)
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a.pushWordToStack(l)
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}
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// popStackWord sets the new stack pointer and returns the appropriate byte in memory
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func (a *Appleone) popStackWord() uint8 {
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a.cpu.sp = uint8((uint16(a.cpu.sp) + 1) & 0xFF)
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return a.mem[StackBottom+uint16(a.cpu.sp)]
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}
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// popStackDWord pops two stack words (a double word - uint16) off the stack
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func (a *Appleone) popStackDWord() uint16 {
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l := a.popStackWord()
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h := a.popStackWord()
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return (uint16(h) << 8) | uint16(l)
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}
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// nextWord returns the next byte in memory
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func (a *Appleone) nextWord() uint8 {
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return a.mem[a.cpu.pc-1]
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}
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// nextDWord returns the next two bytes (double word)
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func (a *Appleone) nextDWord() uint16 {
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return a.littleEndianToUint16(a.mem[a.cpu.pc-1], a.mem[a.cpu.pc-2])
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}
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func (a *Appleone) setZeroIfNeeded(word uint8) {
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a.clearZero()
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if word == 0 {
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a.setZero()
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}
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}
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func (a *Appleone) setZero() {
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a.cpu.ps |= flagZero
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}
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func (a *Appleone) clearZero() {
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a.cpu.sp &^= flagZero
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}
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func (a *Appleone) setNegativeIfOverflow(word uint8) {
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a.clearNegative()
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if word > 127 {
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a.setNegative()
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}
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}
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func (a *Appleone) setNegative() {
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a.cpu.ps |= flagZero
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}
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func (a *Appleone) clearNegative() {
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a.cpu.sp &^= flagZero
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}
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func (a *Appleone) getCarry() uint8 {
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return a.cpu.sp & flagCarry
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}
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func (a *Appleone) setCarry() {
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a.cpu.sp |= flagCarry
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}
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func (a *Appleone) clearCarry() {
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a.cpu.sp &^= flagCarry
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}
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func (a *Appleone) setOverflow() {
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a.cpu.sp |= flagOverflow
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}
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func (a *Appleone) clearOverflow() {
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a.cpu.sp &^= flagOverflow
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}
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