fix for possible cursor-related scren corruption

src/kernal/screen/cursor.s

@@ -50,6 +50,9 @@ cursor_draw:
 
 	bne cursor_blink_timer_reset // branches always
 
+
+// XXX code below is probably not 100% safe
+
 cursor_disable:
 
 	lda #$80
@@ -59,23 +62,27 @@ cursor_disable:
 
 cursor_hide_if_visible:
 
+	// Set countdown to high value, to prevent IRQ interference
+	lda #$FF
+	sta BLNCT
+
+	// If cursor is not visible, nothing to do
 	lda BLNON
-	beq cursor_blink_end
+	beq cursor_blink_timer_reset
 
 	// FALLTROUGH
 
 cursor_undraw:
 
-	// Prevent interrupts from updating cursor
-	lda #0
-	sta BLNON
-
 	jsr screen_get_clipped_PNTR
 	lda GDBLN
 	sta (PNT),y
 	lda GDCOL
 	sta (USER),y
 	
+	lda #0
+	sta BLNON
+
 	// FALLTROUGH
 
 cursor_blink_timer_reset:
@@ -87,4 +94,5 @@ cursor_blink_timer_reset:
 	// FALLTROUGH
 
 cursor_blink_end:
+
 	rts

src/kernal/screen/cursor_show.s

@@ -12,6 +12,7 @@
 
 
 cursor_show_if_enabled:
+
 	lda BLNSW
 	bne cursor_show_end
 	lda BLNON
@@ -36,4 +37,5 @@ cursor_show:
 	// FALLTROUGH
 
 cursor_show_end:
+
 	rts

src/kernal/screen_m65/mega65_cursor.s

@@ -10,10 +10,28 @@
 // - GDCOL (colour under cursor)
 //
 
+
+m65_cursor_disable:       // XXX utilize this!
+
+	// Make sure IRQ won't interfere by increasing the counter      XXX reuse in legacy mode
+	lda #$FF
+	sta BLNCT
+
+	// Disable cursor blinking
+	lda #$80
+	sta BLNSW
+
+	// FALLTHROUGH
+
 m65_cursor_hide_if_visible:
 
+	// Set countdown to high value, to prevent IRQ interference
+	lda #$FF
+	sta BLNCT
+
+	// If cursor is not visible, nothing to do
 	lda BLNON
-	beq m65_cursor_end
+	beq m65_cursor_blink_timer_reset
 
 	// FALLTROUGH
 
@@ -21,8 +39,10 @@ m65_cursor_undraw:
 
 	// XXX provide implementation
 
-	lda #$80
-	sta BLNSW
+
+	// Mark cursor as not drawn
+	lda #0
+	sta BLNON
 
 	rts
 
@@ -35,6 +55,14 @@ m65_cursor_show_if_enabled:
 
 	// FALLTROUGH
 
-m65_cursor_end:
+m65_cursor_blink_timer_reset:    // XXX reuse code from main KERNAL
 
-	rts
+	// Rest blink counter (Mapping the 64, p39-40)
+	lda #20
+	sta BLNCT
+
+	// FALLTROUGH
+
+m65_cursor_blink_end:
+
+	rts