hide cursor when drawing, minor other fixes

c64/kernal/blink_cursor.s

@@ -0,0 +1,51 @@
+	;; We have the following variables:
+	;; cursor_blink_disable
+	;; cursor_blink_countdown
+	;; cursor_saved_character
+	;; cursor_is_visible
+	;; colour_under_cursor
+	
+blink_cursor:
+	;; Is the cursor enabled?
+	bit cursor_blink_disable
+	bne no_blink_cursor
+
+	;; Do we need to redraw things?
+	dec cursor_blink_countdown
+	bpl no_blink_cursor
+
+	;; XXX - Save character colour also!
+	
+	;; Check if cursor was visible or not, and toggle
+	lda cursor_is_visible
+	bne undraw_cursor
+draw_cursor:
+	ldy current_screen_x
+	lda (current_screen_line_ptr),y
+	sta cursor_saved_character
+	eor #$80
+	sta (current_screen_line_ptr),y
+	lda #1
+	sta cursor_is_visible
+	jmp reset_blink_timer
+
+undraw_cursor:
+	lda cursor_saved_character
+	ldy current_screen_x
+	sta (current_screen_line_ptr),y
+	lda #0
+	sta cursor_is_visible
+	;; Fall through
+reset_blink_timer:	
+	;; Rest blink counter
+	;; (Compute's Mapping the 64, p39-40)
+	lda #20
+	sta cursor_blink_countdown
+no_blink_cursor:
+
+	rts
+
+hide_cursor_if_visible:
+	bit cursor_is_visible
+	bne undraw_cursor
+	rts

c64/kernal/chrout.s

@@ -11,10 +11,12 @@ chrout:
 	pha
 	tya
 	pha
+
+	jsr hide_cursor_if_visible
+
 	lda last_printed_character_ascii
 	tax
 	
-
 	;; Check for special characters
 
 	;; Linefeed (simply ignored)

c64/kernal/irq_handler.s

@@ -21,8 +21,10 @@ irq_handler:
 	;; (but only if initialised)
 	lda $0314
 	ora $0315
-	beq no_handler_installed
+	beq default_irq_handler
 	jmp ($0314)
-no_handler_installed:
+default_irq_handler:	
+
+	jsr blink_cursor
 	
 	jmp return_from_interrupt