Added preference setting for misaligned memory access

Disabled by default. When enabled misaligned read and writes will be
reported as memory faults

gui/sdlimgui/win_prefs.go

@@ -591,6 +591,11 @@ a memory address that does not exist.
 Note that the program will always abort if the access is a PC fetch, even if this option is not set.
 
 Illegal accesses will be logged even if program does not abort.`)
+
+	misalignedAccessIsFault := win.img.dbg.VCS().Env.Prefs.ARM.MisalignedAccessIsFault.Get().(bool)
+	if imgui.Checkbox("Treat Misaligned Accesses as Memory Faults", &misalignedAccessIsFault) {
+		win.img.dbg.VCS().Env.Prefs.ARM.MisalignedAccessIsFault.Set(misalignedAccessIsFault)
+	}
 }
 
 func (win *winPrefs) drawPlusROMTab() {

hardware/memory/cartridge/arm/arm.go

@@ -219,9 +219,9 @@ type ARM struct {
 	// prefsPulse ticker slows the rate at which updatePrefs() is called
 	prefsPulse *time.Ticker
 
-	// whether to foce an error on illegal memory access. set from ARM.prefs at
-	// the start of every arm.Run()
-	abortOnMemoryFault bool
+	// read from ARM.prefs every prefsPulse tick
+	abortOnMemoryFault      bool
+	misalignedAccessIsFault bool
 
 	// the speed at which the arm is running at and the required stretching for
 	// access to flash memory. speed is in MHz. Access latency of Flash memory is
@@ -456,8 +456,8 @@ func (arm *ARM) updatePrefs() {
 		arm.Ncycle = arm.nCycle
 	}
 
-	// memory fault handling
 	arm.abortOnMemoryFault = arm.prefs.AbortOnMemoryFault.Get().(bool)
+	arm.misalignedAccessIsFault = arm.prefs.MisalignedAccessIsFault.Get().(bool)
 }
 
 func (arm *ARM) String() string {

hardware/memory/cartridge/arm/memory_access.go

@@ -47,7 +47,9 @@ func (arm *ARM) nullAccess(event string, addr uint32) {
 
 // misalignedAccess is a special condition of illegalAccess()
 func (arm *ARM) misalignedAccess(event string, addr uint32) {
-	arm.memoryFault(event, faults.MisalignedAccess, addr)
+	if arm.misalignedAccessIsFault {
+		arm.memoryFault(event, faults.MisalignedAccess, addr)
+	}
 }
 
 func (arm *ARM) read8bit(addr uint32) uint8 {

hardware/preferences/arm_preferences.go

@@ -47,6 +47,11 @@ type ARMPreferences struct {
 	// abort execution on memory fault (eg. accessing memory that doesn't exist)
 	AbortOnMemoryFault prefs.Bool
 
+	// treat misaligned accesses as a memory fault. (ie. will be reported as a
+	// memory fault and will cause execution to abort if AbortOnMemoryFault is
+	// true)
+	MisalignedAccessIsFault prefs.Bool
+
 	// include disassembly and register details when logging memory faults
 	ExtendedMemoryFaultLogging prefs.Bool
 }
@@ -87,6 +92,10 @@ func newARMprefrences() (*ARMPreferences, error) {
 	if err != nil {
 		return nil, err
 	}
+	err = p.dsk.Add("hardware.arm7.MisalignedAccessIsFault", &p.MisalignedAccessIsFault)
+	if err != nil {
+		return nil, err
+	}
 	err = p.dsk.Add("hardware.arm7.extendedMemoryFaultLogging", &p.ExtendedMemoryFaultLogging)
 	if err != nil {
 		return nil, err
@@ -107,6 +116,7 @@ func (p *ARMPreferences) SetDefaults() {
 	p.Immediate.Set(false)
 	p.MAM.Set(-1)
 	p.AbortOnMemoryFault.Set(false)
+	p.MisalignedAccessIsFault.Set(false)
 	p.ExtendedMemoryFaultLogging.Set(false)
 }