first public release

flow_conditionals_simple_test.go

@@ -0,0 +1,67 @@
+package z80
+
+import "testing"
+
+// Basic conditional flow timing: JR cc, RET cc, CALL cc
+func TestJRcc_RETcc_CALLcc_Timing_Basics(t *testing.T) {
+	cpu, mem, _ := testCPU()
+
+	// Make a small program space
+	// OR A (keeps Z=0), then JR Z,+2 (not taken), then XOR A (Z=1), JR NZ,+2 (not taken), JR Z,+2 (taken)
+	loadProgram(cpu, mem, 0x0000,
+		0xB7,       // OR A (A starts FF; Z=0)
+		0x28, 0x02, // JR Z, +2   -> not taken (7)
+		0xAF,       // XOR A -> A=0 Z=1
+		0x20, 0x02, // JR NZ, +2  -> not taken now (7)
+		0x28, 0x02, // JR Z, +2   -> taken (12)
+		0x00, 0x00,
+	)
+	cpu.A = 0xff // HUMAN: my cpu not set A to FF
+	mustStep(t, cpu)
+	assertEq(t, mustStep(t, cpu), 7, "JR Z not taken")
+	mustStep(t, cpu)
+	assertEq(t, mustStep(t, cpu), 7, "JR NZ not taken")
+	assertEq(t, mustStep(t, cpu), 12, "JR Z taken")
+
+	// RET cc: make a simple CALL, then set flags so condition is false/true
+	cpu, mem, _ = testCPU()
+	cpu.SP = 0xFFFE
+	// CALL next; place RET C (D8) and RET NC (D0) in two spots and test both timings
+	loadProgram(cpu, mem, 0x0000, 0xCD, 0x06, 0x00) // CALL 0006
+	mem.WriteByte(0x0006, 0xD8)                     // RET C
+	cpu.SetFlag(FLAG_C, false)
+	mustStep(t, cpu) // CALL
+	// RET C (not taken): 5 cycles
+	assertEq(t, mustStep(t, cpu), 5, "RET C not taken")
+
+	// Put RET NC; set C so taken path triggers
+	loadProgram(cpu, mem, cpu.PC, 0xCD, 0x06, 0x00)
+	mem.WriteByte(0x0006, 0xD0) // RET NC
+	cpu.SetFlag(FLAG_C, false)
+	pcBefore := cpu.PC
+	mustStep(t, cpu) // CALL
+	// RET NC (taken): 11 cycles
+	c := mustStep(t, cpu)
+	assertEq(t, c, 11, "RET NC taken")
+	assertEq(t, cpu.PC, pcBefore+3, "Returned to next instruction after CALL")
+}
+
+func TestDJNZ_Taken(t *testing.T) {
+	cpu, mem, _ := testCPU()
+	loadProgram(cpu, mem, 0x0000,
+		0x06, 0x02, // LD B,2
+		0x10, 0x02, // DJNZ +2 (B->1, taken)
+	)
+	mustStep(t, cpu) // LD B,2
+	assertEq(t, mustStep(t, cpu), 13, "DJNZ taken")
+}
+
+func TestDJNZ_NotTaken(t *testing.T) {
+	cpu, mem, _ := testCPU()
+	loadProgram(cpu, mem, 0x0000,
+		0x06, 0x01, // LD B,1
+		0x10, 0x02, // DJNZ +2 (B->0, not taken)
+	)
+	mustStep(t, cpu) // LD B,1
+	assertEq(t, mustStep(t, cpu), 8, "DJNZ not taken")
+}