diff --git a/LICENSE.txt b/LICENSE.txt
index 84e20f04..cad5a8fd 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -7,7 +7,7 @@ GPLv2
 ---
 
 https://github.com/gasman/jsspeccy2
-
+Z80 emulator
 GPLv3
 
 ---
diff --git a/index.html b/index.html
index 27712b3b..a2f9782f 100644
--- a/index.html
+++ b/index.html
@@ -142,7 +142,7 @@ if (window.location.host.endsWith('8bitworkshop.com')) {
     <button id="dbg_pause" type="button" title="Pause"><span class="glyphicon glyphicon-pause" aria-hidden="true"></span></button>
     <button id="dbg_go" type="button" title="Run"><span class="glyphicon glyphicon-play" aria-hidden="true"></span></button>
     <button id="dbg_step" type="button" title="Step"><span class="glyphicon glyphicon-step-forward" aria-hidden="true"></span></button>
-    <button id="dbg_tovsync" type="button" title="Single Frame"><span class="glyphicon glyphicon-forward" aria-hidden="true"></span></button>
+    <button id="dbg_tovsync" type="button" title="Next Frame/Interrupt"><span class="glyphicon glyphicon-forward" aria-hidden="true"></span></button>
     <button id="dbg_toline" type="button" title="Run To Line"><span class="glyphicon glyphicon-save" aria-hidden="true"></span></button>
     <button id="dbg_stepout" type="button" title="Step Out of Subroutine"><span class="glyphicon glyphicon-hand-up" aria-hidden="true"></span></button>
     <button id="dbg_stepback" type="button" title="Step Backwards"><span class="glyphicon glyphicon-step-backward" aria-hidden="true"></span></button>
diff --git a/src/platform/sms.ts b/src/platform/sms.ts
index 71b0f809..981f1b46 100644
--- a/src/platform/sms.ts
+++ b/src/platform/sms.ts
@@ -166,10 +166,12 @@ class SG1000Platform extends BaseZ80Platform {
   }
 
   advance(novideo : boolean) {
+    var extraCycles = 0;
     for (var sl=0; sl<this.numTotalScanlines; sl++) {
       this.currentScanline = sl;
-      this.startLineTstates = this.cpu.getTstates();
-      this.runCPU(this.cpu, this.cpuCyclesPerLine);
+      this.startLineTstates = this.cpu.getTstates() + extraCycles;
+      extraCycles = this.runCPU(this.cpu, this.cpuCyclesPerLine - extraCycles); // TODO: HALT opcode?
+      //debug//this.video.getFrameData()[sl] = -1>>>extraCycles;
       this.vdp.drawScanline(sl);
     }
     this.video.updateFrame();
diff --git a/src/video/tms9918a.ts b/src/video/tms9918a.ts
index 60348c24..96832778 100644
--- a/src/video/tms9918a.ts
+++ b/src/video/tms9918a.ts
@@ -501,7 +501,7 @@ export class TMS9918A {
 
     readStatus() : number {
         var i = this.statusRegister;
-        this.statusRegister = 0x1F; // TODO: &= 0x1f?
+        this.statusRegister = 0x1F; // TODO: & 0x1f?
         if (this.interruptsOn) {
             this.cru.setVDPInterrupt(false);
         }
@@ -564,6 +564,7 @@ export class TMS9918A {
                 s += lpad(row[0], w) + ": $" + hex(row[1],4) + " - $" + hex(row[1]+row[2]-1,4) + "\n";
         }
         s += lpad("Address Register",w) + ": $" + hex(this.addressRegister,4) + "\n";
+        s += lpad("Status Register",w) + ": $" + hex(this.statusRegister,2) + "\n";
         s += lpad("Screen Mode",w) + ":  " + this.screenMode + "\n";
         s += lpad("Display On",w) + ":  " + this.displayOn + "\n";
         if (this.ramMask != 0x3fff)
@@ -757,8 +758,7 @@ export class SMSVDP extends TMS9918A {
         this.cram.set(state.cram);
     }
     drawScanline(y:number) {
-        if (this.screenMode == TMS9918A_Mode.MODE4) // TODO: check for other uses
-            //this.drawScanlineMode4(y);
+        if (this.screenMode == TMS9918A_Mode.MODE4)
             this.rasterize_line(y);	// special mode 4
         else
             super.drawScanline(y);