sms: implement button C and Start in Pad

blk/635

@@ -7,7 +7,7 @@
     0x08 ( RIGHT ) OVER AND NOT IF 5 _sel +! THEN
     0x10 ( BUTB ) OVER AND NOT IF _nxtcls THEN
     ( update sel in VDP )
-    _sel C@ (emit) -1 XYPOS +!
+    _chk _sel C@ (emit) -1 XYPOS +!
     ( return whether any of the high 3 bits is low )
     0xe0 AND 0xe0 <
 ;

blk/636

@@ -1,8 +1,9 @@
 : (key)
+    _next C@ IF _next C@ 0 _next C! EXIT THEN
     BEGIN _updsel UNTIL
     _prevstat C@
-    0x20 ( BUTC ) OVER AND NOT IF THEN
-    0x40 ( BUTA ) AND NOT IF THEN
+    0x20 ( BUTC ) OVER AND NOT IF DROP _sel C@ EXIT THEN
+    0x40 ( BUTA ) AND NOT IF EXIT THEN
     ( If not BUTC or BUTA, it has to be START )
-    _sel C@
+    0xd _next C! _sel C@
 ;