From b9603add19a40b8ae88384decb314cf943de070e Mon Sep 17 00:00:00 2001
From: Zellyn Hunter <zellyn@gmail.com>
Date: Wed, 27 Feb 2013 23:01:51 -0800
Subject: [PATCH] Simplest possible text-mode only no-disk Apple II

---
 texty/texty.go | 192 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 192 insertions(+)
 create mode 100644 texty/texty.go

diff --git a/texty/texty.go b/texty/texty.go
new file mode 100644
index 0000000..2c12935
--- /dev/null
+++ b/texty/texty.go
@@ -0,0 +1,192 @@
+// Simplest possible Apple II that will possibly boot. ~ (tilde) to quit.
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"time"
+
+	"github.com/nsf/termbox-go"
+	"github.com/zellyn/go6502/asm"
+	"github.com/zellyn/go6502/cpu"
+)
+
+// Memory for the tests. Satisfies the cpu.Memory interface.
+type Apple2 struct {
+	mem    [65536]byte
+	events chan termbox.Event
+	done   bool
+	key    byte // BUG(zellyn): make reads/writes atomic
+	keys   chan byte
+	debug  bool // Set true and close termbox to start tracing out instructions
+}
+
+// Mapping of screen bytes to character values
+var AppleChars = "@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_ !\"#$%&'()*+,-./0123456789:;<=>?"
+
+// Translate to termbox
+func translateToTermbox(value byte) (char rune, fg, bg termbox.Attribute) {
+	// BUG(zellyn): change this to return char, MODE_ENUM.
+	ch := rune(AppleChars[value&0x3F])
+	if value&0x80 > 0 {
+		return ch, termbox.ColorGreen, termbox.ColorBlack
+	}
+	return ch, termbox.ColorGreen, termbox.ColorBlack + termbox.AttrReverse
+}
+
+func termboxToAppleKeyboard(ev termbox.Event) (key byte, err error) {
+	if ev.Key > 0 && ev.Key <= 32 {
+		return byte(ev.Key), nil
+	}
+	if ev.Ch >= '!' && ev.Ch <= 'Z' || ev.Ch == '^' {
+		return byte(ev.Ch), nil
+	}
+	if ev.Ch >= 'a' && ev.Ch <= 'z' {
+		return byte(ev.Ch - 'a' + 'A'), nil
+	}
+	switch ev.Key {
+	case termbox.KeyBackspace2:
+		return 8, nil // backspace
+	case termbox.KeyArrowLeft:
+		return 8, nil // left arrow
+	case termbox.KeyArrowRight:
+		return 21, nil // right arrow
+	}
+	return 0, fmt.Errorf("hi")
+}
+
+func (a2 *Apple2) Read(address uint16) byte {
+	// Keyboard read
+	if address == 0xC000 {
+		return a2.key
+	}
+	if address == 0xC010 {
+		a2.key &= 0x7F
+		return 0 // BUG(zellyn): return proper value (keydown on IIe, not sure on II+)
+	}
+	return a2.mem[address]
+}
+
+func (a2 *Apple2) Write(address uint16, value byte) {
+	if address >= 0xD000 {
+		termbox.Close()
+		panic(fmt.Sprintln("Write to ROM at address $%04X", address))
+	}
+	if address == 0xC010 {
+		// Clear keyboard strobe
+		a2.key &= 0x7F
+	}
+	a2.mem[address] = value
+	if !a2.debug && address >= 0x0400 && address < 0x0800 {
+		offset := int(address - 0x0400)
+		count := offset & 0x7f
+		if count <= 119 {
+			x := count % 40
+			segment := offset / 128
+			which40 := count / 40
+			y := which40*8 + segment
+			ch, fg, bg := translateToTermbox(value)
+			termbox.SetCell(x+1, y+1, ch, fg, bg)
+			termbox.Flush()
+		}
+	}
+}
+
+func (a2 *Apple2) Init() error {
+	if err := termbox.Init(); err != nil {
+		return err
+	}
+	a2.events = make(chan termbox.Event)
+	a2.keys = make(chan byte, 16)
+	go func() {
+		for {
+			a2.events <- termbox.PollEvent()
+		}
+	}()
+	return nil
+}
+func (a2 *Apple2) Close() {
+	termbox.Close()
+}
+
+func (a2 *Apple2) ProcessEvents() {
+	select {
+	case ev := <-a2.events:
+		if ev.Type == termbox.EventKey && ev.Ch == '~' {
+			a2.done = true
+		}
+		if ev.Type == termbox.EventKey {
+			if key, err := termboxToAppleKeyboard(ev); err == nil {
+				a2.keys <- key | 0x80
+			}
+		}
+	default:
+	}
+
+	if a2.key&0x80 == 0 {
+		select {
+		case key := <-a2.keys:
+			a2.key = key
+		default:
+		}
+	}
+}
+
+// Cycle counter for the tests. Satisfies the cpu.Ticker interface.
+type CycleCount uint64
+
+func (c *CycleCount) Tick() {
+	*c += 1
+}
+
+// printStatus prints out the current CPU instruction and register status.
+func printStatus(c cpu.Cpu, m *[65536]byte) {
+	bytes, text, _ := asm.Disasm(c.PC(), m[c.PC()], m[c.PC()+1], m[c.PC()+2])
+	fmt.Printf("$%04X: %s  %s  A=$%02X X=$%02X Y=$%02X SP=$%02X P=$%08b\n",
+		c.PC(), bytes, text, c.A(), c.X(), c.Y(), c.SP(), c.P())
+}
+
+// Run the emulator
+func RunEmulator() {
+	bytes, err := ioutil.ReadFile("../data/roms/apple2+.rom")
+	if err != nil {
+		panic("Cannot read ROM file")
+	}
+	var a2 Apple2
+	ROM_OFFSET := 0xD000
+	copy(a2.mem[ROM_OFFSET:ROM_OFFSET+len(bytes)], bytes)
+	a2.Init()
+	var cc CycleCount
+	c := cpu.NewCPU(&a2, &cc, cpu.VERSION_6502)
+	c.Reset()
+	for !a2.done {
+		// // LIST
+		// if c.PC() == 0xD6A5 {
+		// 	termbox.Close()
+		// 	a2.debug = true
+		// }
+		// // End of LIST
+		// if c.PC() == 0xD729 {
+		// 	break
+		// }
+		if !a2.debug {
+			a2.ProcessEvents()
+		}
+		if a2.debug {
+			printStatus(c, &a2.mem)
+		}
+		err := c.Step()
+		if err != nil {
+			fmt.Println(err)
+			break
+		}
+		time.Sleep(1 * time.Nanosecond) // So the keyboard-reading goroutines can run
+	}
+	if !a2.debug {
+		a2.Close()
+	}
+}
+
+func main() {
+	RunEmulator()
+}