From 94c6ecd97dc835fb55708d1ea8080e9ced557a77 Mon Sep 17 00:00:00 2001
From: Will Angenent <will.angenent@ntt.eu>
Date: Tue, 15 May 2018 11:12:38 +0100
Subject: [PATCH] Added some comments to the audio samples calculation

---
 appleiie.go        |  3 ++-
 audio/audio.go     | 13 +++++++---
 bell_test.go       | 63 ++++++++++++++++++++++++++++++++++++++++++++++
 cpu/cpu.go         | 12 ++++++---
 cpu/cpu_test.go    |  2 +-
 dos33_boot_test.go |  3 ++-
 6 files changed, 85 insertions(+), 11 deletions(-)
 create mode 100644 bell_test.go

diff --git a/appleiie.go b/appleiie.go
index 2ce847b..a767e3d 100644
--- a/appleiie.go
+++ b/appleiie.go
@@ -53,7 +53,8 @@ func update(screen *ebiten.Image) error {
 
 	system.FrameCycles = 0
 	system.LastAudioCycles = 0
-	cpu.Run(*showInstructions, breakAddress, *disableFirmwareWait, system.CpuFrequency/60)
+	exitAtBreak := true
+	cpu.Run(*showInstructions, breakAddress, exitAtBreak, *disableFirmwareWait, system.CpuFrequency/60)
 	audio.ForwardToFrameCycle()
 	system.Cycles += system.FrameCycles
 	system.FrameCycles = 0
diff --git a/audio/audio.go b/audio/audio.go
index fa1c480..29d2d8e 100644
--- a/audio/audio.go
+++ b/audio/audio.go
@@ -20,11 +20,16 @@ func attenuate(sample int16) int16 {
 }
 
 func ForwardToFrameCycle() {
-	ratio := float64(system.AudioSampleRate) / system.CpuFrequency
+	// 1023000/44100=23.19 cycles per audio sample
+	cyclesPerAudioSample := system.CpuFrequency / float64(system.AudioSampleRate)
 
-	samples := uint64(ratio * float64(system.FrameCycles-system.LastAudioCycles))
-	var i uint64
-	for i = 0; i < samples; i++ {
+	// Should be about 1023000/60=17050
+	elapsedCycles := system.FrameCycles - system.LastAudioCycles
+
+	// Should be about 17050/23.19=735 audio samples per frame
+	audioSamples := uint64(float64(elapsedCycles) / cyclesPerAudioSample)
+
+	for i := uint64(0); i < audioSamples; i++ {
 		b := attenuate(system.LastAudioValue)
 		system.AudioChannel <- b
 	}
diff --git a/bell_test.go b/bell_test.go
new file mode 100644
index 0000000..f806480
--- /dev/null
+++ b/bell_test.go
@@ -0,0 +1,63 @@
+package main
+
+import (
+	"fmt"
+	"mos6502go/cpu"
+	"mos6502go/keyboard"
+	"mos6502go/mmu"
+	"mos6502go/system"
+	"mos6502go/video"
+	"testing"
+)
+
+func testBellCycles(delay int) {
+	cpu.State.PC = 0x800
+	mmu.WriteMemory(0x800, 0xa9) // LDA #$xx
+	mmu.WriteMemory(0x801, uint8(delay))
+	mmu.WriteMemory(0x802, 0x20) // JSR $fca8
+	mmu.WriteMemory(0x803, 0xa8)
+	mmu.WriteMemory(0x804, 0xfc)
+	mmu.WriteMemory(0x805, 0x00) // Break address
+
+	system.FrameCycles = 0
+	showInstructions := false
+	breakAddress := uint16(0x805)
+	exitAtBreak := false
+	disableFirmwareWait := false
+	cpu.Run(showInstructions, &breakAddress, exitAtBreak, disableFirmwareWait, system.CpuFrequency*1000)
+
+	// See http://apple2.org.za/gswv/a2zine/GS.WorldView/Resources/USEFUL.TABLES/WAIT.DELAY.CR.txt
+	expectedCycles := (26 + 27*delay + 5*delay*delay) / 2
+
+	gotCycles := int(system.FrameCycles - 2)
+	fmt.Printf("Delay %3d ", delay)
+	if gotCycles == expectedCycles {
+		fmt.Println("OK")
+
+	} else {
+		fmt.Printf("Failed expected %6d, got %6d\n", expectedCycles, gotCycles)
+	}
+}
+
+func TestBell(t *testing.T) {
+	cpu.InitInstructionDecoder()
+	mmu.InitRAM()
+	mmu.InitApple2eROM()
+	mmu.InitIO()
+	cpu.Init()
+	keyboard.Init()
+	video.Init()
+	system.Init()
+
+	testBellCycles(1)
+	testBellCycles(2)
+	testBellCycles(3)
+	testBellCycles(4)
+	testBellCycles(12)
+	testBellCycles(0x10)
+	testBellCycles(0x20)
+	testBellCycles(0x40)
+	testBellCycles(0x80)
+	testBellCycles(0xc0)
+	testBellCycles(0xff)
+}
diff --git a/cpu/cpu.go b/cpu/cpu.go
index 2e72dcb..ba68dbf 100644
--- a/cpu/cpu.go
+++ b/cpu/cpu.go
@@ -530,7 +530,7 @@ func nmi() {
 	system.FrameCycles += 7
 }
 
-func Run(showInstructions bool, breakAddress *uint16, disableFirmwareWait bool, wantedCycles uint64) {
+func Run(showInstructions bool, breakAddress *uint16, exitAtBreak bool, disableFirmwareWait bool, wantedCycles uint64) {
 	system.FrameCycles = 0
 
 	for {
@@ -568,9 +568,13 @@ func Run(showInstructions bool, breakAddress *uint16, disableFirmwareWait bool,
 		addressMode := OpCodes[opcode].AddressingMode.Mode
 
 		if breakAddress != nil && State.PC == *breakAddress {
-			fmt.Printf("Break at $%04x\n", *breakAddress)
-			PrintInstruction(true)
-			os.Exit(0)
+			if exitAtBreak {
+				fmt.Printf("Break at $%04x\n", *breakAddress)
+				PrintInstruction(true)
+				os.Exit(0)
+			} else {
+				return
+			}
 		}
 
 		switch opcode {
diff --git a/cpu/cpu_test.go b/cpu/cpu_test.go
index 1d6a454..f0f67cc 100644
--- a/cpu/cpu_test.go
+++ b/cpu/cpu_test.go
@@ -73,7 +73,7 @@ func TestCPU(t *testing.T) {
 
 		keyboard.Init()
 
-		cpu.Run(*showInstructions, breakAddress, false, 0)
+		cpu.Run(*showInstructions, breakAddress, true, false, 0)
 		fmt.Printf("Finished running %s\n\n", rom)
 	}
 }
diff --git a/dos33_boot_test.go b/dos33_boot_test.go
index b52106c..a4294d7 100644
--- a/dos33_boot_test.go
+++ b/dos33_boot_test.go
@@ -29,9 +29,10 @@ func TestDOS33Boot(t *testing.T) {
 	system.LastAudioCycles = 0
 	showInstructions := false
 	var breakAddress uint16
+	exitAtBreak := true
 	disableFirmwareWait := false
 	t0 := time.Now()
-	cpu.Run(showInstructions, &breakAddress, disableFirmwareWait, system.CpuFrequency*1000)
+	cpu.Run(showInstructions, &breakAddress, exitAtBreak, disableFirmwareWait, system.CpuFrequency*1000)
 
 	elapsed := float64(time.Since(t0) / time.Millisecond)
 	fmt.Printf("CPU Cycles:    %d\n", system.FrameCycles)