o debugger

- a recent refactor caused the vcs to initialise with the basic
    television rather than the sdl gui/tv
    - this meant that the sdl implementation of MetaSignal was not being
    called

o basic television
    - scanline extension corrected

o errors
    - messages corrected

debugger/debugger.go

@@ -149,7 +149,7 @@ func NewDebugger() (*Debugger, error) {
 	dbg.gui.SetFeature(gui.ReqSetAllowDebugging, true)
 
 	// create a new VCS instance
-	dbg.vcs, err = hardware.NewVCS(btv)
+	dbg.vcs, err = hardware.NewVCS(dbg.gui)
 	if err != nil {
 		return nil, errors.NewFormattedError(errors.DebuggerError, err)
 	}

errors/messages.go

@@ -71,12 +71,12 @@ var messages = map[Errno]string{
 	UnknownPeriphEvent:        "periperal error: %s: unsupported event (%v)",
 
 	// tv
-	UnknownTVRequest: "tv error: unsupported tv request (%v)",
+	UnknownTVRequest: "tv error: unsupported request (%v)",
 	BasicTelevision:  "tv error: BasicTelevision: %s",
 	ImageTV:          "tv error: ImageTV: %s",
 	DigestTV:         "tv error: DigestTV: %s",
 
 	// gui
-	UnknownGUIRequest: "gui error: unsupported gui request (%v)",
+	UnknownGUIRequest: "gui error: unsupported request (%v)",
 	SDL:               "gui error: SDL: %s",
 }

television/basic.go

@@ -216,7 +216,7 @@ func (btv *BasicTelevision) Signal(sig SignalAttributes) error {
 
 	// push screen limits outwards as required
 	if !sig.VBlank {
-		if btv.endOfScreen && btv.scanline > btv.pendingVisibleBottom {
+		if !btv.endOfScreen && btv.scanline > btv.pendingVisibleBottom {
 			btv.pendingVisibleBottom = btv.scanline + 2
 
 			// keep within limits