save X and Y in CHROUT

c64/kernal/chrout.s

@@ -1,9 +1,29 @@
 ; Function defined on pp272-273 of C64 Programmers Reference Guide
 chrout:
 	;; Crude implementation of character output	
+
+	;; Save X and Y values
+	;; (Confirmed by writing a test program that X and Y
+	;; don't get modified, in agreement with C64 PRG's
+	;; description of CHROUT)
+	sta last_printed_character_ascii
+	txa
+	pha
+	tya
+	pha
+	lda last_printed_character_ascii
 	
 	;; Write character on the screen
 	ldy current_screen_x
+
+	;;  Convert PETSCII to screen code
+	cmp #$40
+	bcc chrout_l1
+	cmp #$59
+	bcs chrout_l1
+	and #$1f
+
+chrout_l1:	
 	sta (current_screen_line_ptr),y
 
 	;; Advance the column, and scroll screen down if we need
@@ -13,9 +33,19 @@ chrout:
 	iny
 	sty current_screen_x
 	cpy #40
-	beq screen_grow_logical_line
+	bne no_screen_advance_to_next_line
+	jsr screen_grow_logical_line
 	cpy #79
-	bcs screen_advance_to_next_line
+	bcc no_screen_advance_to_next_line
+	jsr screen_advance_to_next_line
+no_screen_advance_to_next_line:
+
+	;; Restore X and Y
+	pla
+	tay
+	pla
+	tax
+	
 	rts
 
 screen_grow_logical_line: