Add Cpu program loading

cpu.go

@@ -8,9 +8,10 @@ type Cpu struct {
 }
 
 const (
-	ResetVector = 0xFFFC
+	ResetVector = 0xFFFC // 0xFFFC-FFFD
 )
 
+// Create an new Cpu instance with the specified AddressBus
 func NewCpu(bus *AddressBus) (*Cpu, error) {
 	return &Cpu{bus: bus}, nil
 }
@@ -19,7 +20,18 @@ func (c *Cpu) HasAddressBus() bool {
 	return c.bus != nil
 }
 
+// Reset the CPU, emulating the RESB pin.
 func (c *Cpu) Reset() {
 	c.PC = c.bus.Read16(ResetVector)
 	c.P = 0x34
 }
+
+// Load the specified program data at the given memory location
+// and point the Program Counter to the beginning of the program
+func (c *Cpu) LoadProgram(data []byte, location uint16) {
+	for i, b := range data {
+		c.bus.Write(location+uint16(i), b)
+	}
+
+	c.PC = location
+}

cpu_test.go

@@ -12,6 +12,8 @@ func NewRamMachine() (*Cpu, *AddressBus, *Ram) {
 	bus.Attach(ram, 0x0000)
 	cpu, _ := NewCpu(bus)
 
+	cpu.Reset()
+
 	return cpu, bus, ram
 }
 
@@ -29,7 +31,7 @@ func TestCpuAddressBus(t *testing.T) {
 	assert.True(cpu.HasAddressBus())
 }
 
-func TestCpuState(t *testing.T) {
+func TestCpuReset(t *testing.T) {
 	assert := assert.New(t)
 
 	cpu, _, _ := NewRamMachine()
@@ -46,3 +48,18 @@ func TestCpuState(t *testing.T) {
 	// Read PC from $FFFC-FFFD
 	assert.Equal(0x1234, cpu.PC)
 }
+
+func TestProgramLoading(t *testing.T) {
+	assert := assert.New(t)
+
+	program := []byte{0xEA, 0xEB, 0xEC}
+
+	cpu, bus, _ := NewRamMachine()
+	cpu.LoadProgram(program, 0x0300)
+
+	assert.Equal(0xEA, bus.Read(0x0300))
+	assert.Equal(0xEB, bus.Read(0x0301))
+	assert.Equal(0xEC, bus.Read(0x0302))
+
+	assert.Equal(0x0300, cpu.PC)
+}