Implement more CPU instructions

gb/cpu_test.go

@@ -54,16 +54,16 @@ func TestInstruction00(t *testing.T) {
 
 	cpu.Step()
 
-	assert.Equal(t, cpu.Regs.PC, uint16(0x01))
+	assert.Equal(t, uint16(0x01), cpu.Regs.PC)
 }
 
 func TestInstruction3C(t *testing.T) {
 	// Should increment A register
 	cpu := createCPU([]byte{0x3C, 0x00, 0x00})
 
-	assert.Equal(t, cpu.Regs.A, byte(0x0))
+	assert.Equal(t, byte(0x0), cpu.Regs.A)
 	cpu.Step()
-	assert.Equal(t, cpu.Regs.A, byte(0x01))
+	assert.Equal(t, byte(0x01), cpu.Regs.A)
 
 	// Should clear Zero Flag
 	cpu = createCPU([]byte{0x3C, 0x00, 0x00})
@@ -108,7 +108,7 @@ func TestInstructionC3(t *testing.T) {
 
 	cpu.Step()
 
-	assert.Equal(t, cpu.Regs.PC, uint16(0x150))
+	assert.Equal(t, uint16(0x150), cpu.Regs.PC)
 }
 
 func TestInstructionE9(t *testing.T) {
@@ -118,5 +118,52 @@ func TestInstructionE9(t *testing.T) {
 
 	cpu.Step()
 
-	assert.Equal(t, cpu.Regs.PC, uint16(0x1234))
+	assert.Equal(t, uint16(0x1234), cpu.Regs.PC)
+}
+
+func TestInstructionF3(t *testing.T) {
+	cpu := createCPU([]byte{0xF3, 0x00, 0x00})
+
+	cpu.InterruptMasterEnable = true
+	cpu.Step()
+
+	assert.False(t, cpu.InterruptMasterEnable)
+}
+
+func TestInstruction31(t *testing.T) {
+	cpu := createCPU([]byte{0x31, 0xFF, 0xCF})
+
+	cpu.Step()
+
+	// Should load SP with n16 value
+	assert.Equal(t, uint16(0xCFFF), cpu.Regs.SP)
+
+	// Should step over the 16 bit value onto the next instruction, i.e. increase the program counter with 3.
+	assert.Equal(t, uint16(0x0003), cpu.Regs.PC)
+}
+
+func TestInstructionCD(t *testing.T) {
+	cpu := createCPU([]byte{0xCD, 0x4C, 0x48, 0x41})
+
+	cpu.Step()
+
+	// Should push the address of the next instruction onto the stack
+	// In this case 0x41 which is at address 0x03 (i.e. the 4th instruction in the row above creating the CPU instance)
+	assert.Equal(t, uint16(0x03), cpu.Bus.Read16(cpu.Regs.SP))
+
+	// Should jump to n16 value
+	assert.Equal(t, uint16(0x484C), cpu.Regs.PC)
+}
+
+func TestInstruction21(t *testing.T) {
+	cpu := createCPU([]byte{0x21, 0x34, 0x12})
+
+	cpu.Step()
+
+	// Should load the 16-bit immediate value into the combined HL register
+	assert.Equal(t, byte(0x12), cpu.Regs.H)
+	assert.Equal(t, byte(0x34), cpu.Regs.L)
+
+	// Should increase the stack pointer
+	assert.Equal(t, uint16(0x3), cpu.Regs.PC)
 }