BIT instruction; Bit Test.

Author: pda

cpu/cpu.go

@@ -218,6 +218,8 @@ func (c *Cpu) execute(in Instruction) {
 		c.BCS(in)
 	case beq:
 		c.BEQ(in)
+	case bit:
+		c.BIT(in)
 	case bmi:
 		c.BMI(in)
 	case bne:
@@ -361,6 +363,14 @@ func (c *Cpu) BEQ(in Instruction) {
 	}
 }
 
+// BIT: Bit Test.
+func (c *Cpu) BIT(in Instruction) {
+	value := c.resolveOperand(in)
+	c.setStatus(sZero, value&c.AC == 0)
+	c.setStatus(sOverflow, value&(1<<6) != 0)
+	c.setStatus(sNegative, value&(1<<7) != 0)
+}
+
 // BMI: Branch if negative.
 func (c *Cpu) BMI(in Instruction) {
 	if c.getStatus(sNegative) {

cpu/cpu_test.go

@@ -0,0 +1,38 @@
+package cpu
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/pda/go6502/bus"
+	"github.com/pda/go6502/memory"
+)
+
+func createCpu() *Cpu {
+	ram := &memory.Ram{}
+	addressBus, _ := bus.CreateBus()
+	addressBus.Attach(ram, "ram", 0x8000) // upper 32K
+	cpu := &Cpu{Bus: addressBus}
+	cpu.Reset()
+	return cpu
+}
+
+func TestBitInstruction(t *testing.T) {
+	cpu := createCpu()
+	cpu.Bus.Write(0x8000, 0xAA)
+
+	instruction := Instruction{OpType: optypes[0x2C], Op16: 0x8000}
+	expectedName := "BIT absolute $8000"
+	actualName := instruction.String()
+	if actualName != expectedName {
+		t.Error(fmt.Sprintf("expected %s, got %s\n", expectedName, actualName))
+	}
+
+	cpu.BIT(instruction)
+
+	expectedStatus := "n-_b-iz-"
+	actualStatus := cpu.statusString()
+	if actualStatus != expectedStatus {
+		t.Error(fmt.Sprintf("SR expected %s got %s\n", expectedStatus, actualStatus))
+	}
+}