Add ROM Memory

ram_test.go

@@ -6,21 +6,18 @@ import (
 )
 
 func TestRamSize(t *testing.T) {
-	assert := assert.New(t)
-
 	ram, _ := NewRam(0x8000) // 32 kB
-	assert.Equal(0x8000, ram.Size())
+	assert.Equal(t, 0x8000, ram.Size())
 }
 
 func TestRamReadWrite(t *testing.T) {
-	assert := assert.New(t)
 	ram, _ := NewRam(0x8000) // 32 kB
 
 	// Ram zeroed out initially
 	for i := 0; i < 0x8000; i++ {
-		assert.Equal(0x00, ram.data[i])
+		assert.Equal(t, 0x00, ram.data[i])
 	}
 
 	ram.Write(0x1000, 0x42)
-	assert.Equal(0x42, ram.Read(0x1000))
+	assert.Equal(t, 0x42, ram.Read(0x1000))
 }

rom.go

@@ -0,0 +1,38 @@
+package i6502
+
+import (
+	"fmt"
+	"io/ioutil"
+)
+
+/*
+Read-Only Memory
+*/
+type Rom struct {
+	data []byte
+}
+
+/*
+Create a new Rom component, using the content of `path`. The file automatically
+specifies the size of Rom.
+*/
+func NewRom(path string) (*Rom, error) {
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Rom{data: data}, nil
+}
+
+func (r *Rom) Size() uint16 {
+	return uint16(len(r.data))
+}
+
+func (r *Rom) Read(address uint16) byte {
+	return r.data[address]
+}
+
+func (r *Rom) Write(address uint16, data byte) {
+	panic(fmt.Errorf("Trying to write to ROM at 0x%04X", address))
+}

rom_test.go

@@ -0,0 +1,39 @@
+package i6502
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func Test8kRoms(t *testing.T) {
+	rom, err := NewRom("test/8kb.rom")
+
+	assert.Nil(t, err)
+	assert.Equal(t, 0x2000, rom.Size())
+	assert.Equal(t, 0x01, rom.Read(0x0000))
+	assert.Equal(t, 0xFF, rom.Read(0x2000-1))
+}
+
+func TestRomWritePanic(t *testing.T) {
+	rom, _ := NewRom("test/8kb.rom")
+
+	// Writing to rom should panic
+	assert.Panics(t, func() {
+		rom.Write(0x1337, 0x42)
+	}, "Writing to Rom should panic")
+}
+
+func Test16kRom(t *testing.T) {
+	rom, err := NewRom("test/16kb.rom")
+
+	assert.Nil(t, err)
+	assert.Equal(t, 0x4000, rom.Size())
+	assert.Equal(t, 0x01, rom.Read(0x0000))
+	assert.Equal(t, 0xFF, rom.Read(0x4000-1))
+}
+
+func TestRomNotFound(t *testing.T) {
+	rom, err := NewRom("test/does-not-exists.rom")
+	assert.NotNil(t, err)
+	assert.Nil(t, rom)
+}