diff --git a/bank_switch_test.go b/bank_switch_test.go
index 9a9d2d4..29a19ff 100644
--- a/bank_switch_test.go
+++ b/bank_switch_test.go
@@ -11,6 +11,15 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func assertMemoryConfiguration(t *testing.T, address uint16, upperRamReadOnly bool, upperReadMappedToROM bool, d000Bank int) {
+	mmu.WriteMemory(address, 0x00)
+	assert.Equal(t, upperReadMappedToROM, mmu.UpperReadMappedToROM)
+	assert.Equal(t, d000Bank, mmu.D000Bank)
+}
+
+// TestBankSwitching tests the area starting at $d000 and managed by $c08x.
+// First the initial settings are checked. Then a bunch of assertions on the
+// internal code. Then writes to $c08x.
 func TestBankSwitching(t *testing.T) {
 	cpu.InitInstructionDecoder()
 	mmu.InitRAM()
@@ -79,17 +88,7 @@ func TestBankSwitching(t *testing.T) {
 	assert.Equal(t, uint8(0x6f), mmu.ReadMemory(0xd000)) // read from ROM
 	assert.Equal(t, uint8(0xc3), mmu.ReadMemory(0xffff)) // read from ROM
 
-	testSwitches(t)
-}
-
-func assertMemoryConfiguration(t *testing.T, address uint16, upperRamReadOnly bool, upperReadMappedToROM bool, d000Bank int) {
-	mmu.WriteMemory(address, 0x00)
-	// assert.Equal(t, upperRamReadOnly, mmu.UpperRamReadOnly)
-	assert.Equal(t, upperReadMappedToROM, mmu.UpperReadMappedToROM)
-	assert.Equal(t, d000Bank, mmu.D000Bank)
-}
-
-func testSwitches(t *testing.T) {
+	// Test writes to 0xc08x lead to correct memory configurations
 	assertMemoryConfiguration(t, 0xc080, true, false, 2)
 	assertMemoryConfiguration(t, 0xc081, false, true, 2)
 	assertMemoryConfiguration(t, 0xc082, true, true, 2)
diff --git a/bell_test.go b/bell_test.go
index 1fbf9d6..08fb104 100644
--- a/bell_test.go
+++ b/bell_test.go
@@ -5,32 +5,33 @@ import (
 	"testing"
 
 	"github.com/freewilll/apple2/cpu"
-	"github.com/freewilll/apple2/keyboard"
 	"github.com/freewilll/apple2/mmu"
 	"github.com/freewilll/apple2/system"
-	"github.com/freewilll/apple2/video"
 )
 
 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
+	// Add some code to $800
+	mmu.WriteMemory(0x800, 0xa9)         // LDA #delay
+	mmu.WriteMemory(0x801, uint8(delay)) //
+	mmu.WriteMemory(0x802, 0x20)         // JSR $fca8 BELL
+	mmu.WriteMemory(0x803, 0xa8)         //
+	mmu.WriteMemory(0x804, 0xfc)         //
+	mmu.WriteMemory(0x805, 0x00)         // BRK
 
+	// Run the code until the BRK instruction and count the cycles
 	system.FrameCycles = 0
 	showInstructions := false
 	breakAddress := uint16(0x805)
 	exitAtBreak := false
 	disableFirmwareWait := false
+	cpu.State.PC = 0x800
 	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)
+	gotCycles := int(system.FrameCycles - 2) // Exclude the cycles taken by the LDA
+
 	fmt.Printf("Delay %3d ", delay)
 	if gotCycles == expectedCycles {
 		fmt.Println("OK")
@@ -40,14 +41,15 @@ func testBellCycles(delay int) {
 	}
 }
 
+// TestBell tests the nunber of cycles in the system BELL loop for different
+// values of the accumulator. This test was mainly used to diagnose a bug
+// related to sound frequencies being incorrect due to invalid cycle
+// housekeeping in the CPU branch code.
 func TestBell(t *testing.T) {
 	cpu.InitInstructionDecoder()
 	mmu.InitRAM()
 	mmu.InitApple2eROM()
-	mmu.InitIO()
 	cpu.Init()
-	keyboard.Init()
-	video.Init()
 	system.Init()
 
 	testBellCycles(1)
diff --git a/cmd/disasm.go b/cmd/disasm.go
index 10fcd55..e3eb477 100644
--- a/cmd/disasm.go
+++ b/cmd/disasm.go
@@ -1,7 +1,11 @@
 package main
 
+// Command line tool to disassemble a range of addresses
+
 import (
 	"flag"
+	"fmt"
+	"os"
 
 	"github.com/freewilll/apple2/cpu"
 	"github.com/freewilll/apple2/mmu"
@@ -9,6 +13,14 @@ import (
 )
 
 func main() {
+	var Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "Usage of %s:\n\n", os.Args[0])
+		fmt.Fprintf(flag.CommandLine.Output(), "Synopsis:\n    %s -start ADDRESS [-end ADDRESS]\n\n", os.Args[0])
+		fmt.Fprintf(flag.CommandLine.Output(), "Example:\n    %s -start d000 -end ffff\n\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Usage = Usage
+
 	startString := flag.String("start", "", "Start address")
 	endString := flag.String("end", "", "End address")
 	flag.Parse()
diff --git a/dos33_boot_test.go b/dos33_boot_test.go
index a76afd2..56db44d 100644
--- a/dos33_boot_test.go
+++ b/dos33_boot_test.go
@@ -16,14 +16,8 @@ import (
 
 const dosDiskImage = "dos33.dsk"
 
-func runDos33Boot(t *testing.T) {
-	// Boot up DOS3.3
-	utils.RunUntilBreakPoint(t, 0x0801, 2, false, "Boot0")
-	utils.RunUntilBreakPoint(t, 0xb700, 1, false, "Boot1") // $3700 is for master disk, $b700 for a slave disk
-	utils.RunUntilBreakPoint(t, 0x9d84, 3, false, "Boot2")
-	utils.RunUntilBreakPoint(t, 0xd7d2, 2, false, "JMP to basic interpreter NEWSTT")
-}
-
+// TestDOS33Boot goes through the boot process and asserts that the code ends
+// up in the BASIC interpreter after DOS has loaded.
 func TestDOS33Boot(t *testing.T) {
 	cpu.InitInstructionDecoder()
 	mmu.InitRAM()
@@ -39,7 +33,11 @@ func TestDOS33Boot(t *testing.T) {
 
 	t0 := time.Now()
 
-	runDos33Boot(t)
+	// Boot up DOS3.3
+	utils.RunUntilBreakPoint(t, 0x0801, 2, false, "Boot0")
+	utils.RunUntilBreakPoint(t, 0xb700, 1, false, "Boot1") // $3700 is for master disk, $b700 for a slave disk
+	utils.RunUntilBreakPoint(t, 0x9d84, 3, false, "Boot2")
+	utils.RunUntilBreakPoint(t, 0xd7d2, 2, false, "JMP to basic interpreter NEWSTT")
 
 	elapsed := float64(time.Since(t0) / time.Millisecond)
 	fmt.Printf("CPU Cycles:    %d\n", system.FrameCycles)
diff --git a/io_test.go b/io_test.go
index 3518305..3712967 100644
--- a/io_test.go
+++ b/io_test.go
@@ -11,6 +11,7 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+// TestIoBankSwitching tests the switching of the IO memory ROM at $c000-$c7ff
 func TestIoBankSwitching(t *testing.T) {
 	cpu.InitInstructionDecoder()
 	mmu.InitRAM()
diff --git a/prodos_boot_test.go b/prodos_boot_test.go
index bd018e6..752ea77 100644
--- a/prodos_boot_test.go
+++ b/prodos_boot_test.go
@@ -16,7 +16,9 @@ import (
 
 const prodosDiskImage = "prodos19.dsk"
 
-func TestProdosBoot(t *testing.T) {
+// TestProdos19Boot goes through the boot process and asserts that the code ends
+// up in the BASIC interpreter after Prodos has loaded.
+func TestProdos19Boot(t *testing.T) {
 	cpu.InitInstructionDecoder()
 	mmu.InitRAM()
 	mmu.InitApple2eROM()
@@ -40,7 +42,7 @@ func TestProdosBoot(t *testing.T) {
 	utils.RunUntilBreakPoint(t, 0xd000, 1, false, "First call to MLI kernel")
 	utils.RunUntilBreakPoint(t, 0x0800, 2, false, "BI loader")
 	utils.RunUntilBreakPoint(t, 0x2000, 2, false, "BI Relocator")
-	utils.RunUntilBreakPoint(t, 0xbe00, 52, false, "BI Start")
+	utils.RunUntilBreakPoint(t, 0xbe00, 1, false, "BI Start")
 
 	elapsed := float64(time.Since(t0) / time.Millisecond)
 	fmt.Printf("CPU Cycles:    %d\n", system.FrameCycles)
diff --git a/rwts_write_test.go b/rwts_write_test.go
index 071bca2..dafa291 100644
--- a/rwts_write_test.go
+++ b/rwts_write_test.go
@@ -14,12 +14,16 @@ import (
 
 const rwtsDosDiskImage = "dos33.dsk"
 
+// Write a number of bytes to an address
 func writeBytes(address int, data []uint8) {
 	for i := 0; i < len(data); i++ {
 		mmu.WriteMemory(uint16(address)+uint16(i), data[i])
 	}
 }
 
+// TestDos33RwtsWriteRead goes through the boot process and then calls RWTS
+// with a write and read request. Then the result of the read is cheked to make
+// sure it maches the write. This tests the disk image IO code.
 func TestDos33RwtsWriteRead(t *testing.T) {
 	// Test writing and reading a sector using DOS 3.3's RWTS
 	cpu.InitInstructionDecoder()
@@ -75,6 +79,7 @@ func TestDos33RwtsWriteRead(t *testing.T) {
 	writeBytes(start+0x2e, []uint8{0x20, 0xd9, 0x03})                // JSR $03D9      RWTS
 	writeBytes(start+0x31, []uint8{0x00})                            // BRK
 
+	// Run until the RWTS write returns
 	cpu.State.PC = uint16(start)
 	utils.RunUntilBreakPoint(t, 0xb944, 128, false, "RWTS RDADDR")
 	utils.RunUntilBreakPoint(t, 0xb82a, 8, false, "RWTS WRITESEC")
@@ -92,6 +97,7 @@ func TestDos33RwtsWriteRead(t *testing.T) {
 	writeBytes(start+0x1b, []uint8{0xa0, 0x09})                     // LDY #$09
 	writeBytes(start+0x1d, []uint8{0x91, 0x00})                     // STA ($00),Y
 
+	// Run until the RWTS read returns
 	cpu.State.PC = uint16(start)
 	utils.RunUntilBreakPoint(t, uint16(start+0x31), 1, false, "Read routine break")