keyboard part of CHRIN now preserves .Y

STATUS.md

@@ -132,7 +132,7 @@ NOTE: Even the 'DONE' routines won't support features described as missing in on
 | `$FFC6`   | `$F20E`    | `CHKIN`     | DONE     |                                                      |
 | `$FFC9`   | `$F250`    | `CKOUT`     | DONE     |                                                      |
 | `$FFCC`   | `$F333`    | `CLRCHN`    | DONE     |                                                      |
-| `$FFCF`   | `$F157`    | `CHRIN`     | PARTIAL  | no screen support, keyboard does not preserve .Y     |
+| `$FFCF`   | `$F157`    | `CHRIN`     | PARTIAL  | no screen device support                             |
 | `$FFD2`   | `$F1CA`    | `CHROUT`    | DONE     |                                                      |
 | `$FFD5`   | `$F49E`    | `LOAD`      | DONE     |                                                      |
 | `($0330)` | `$F4A5`    | `LOAD`      | DONE     |                                                      |

c64/aliases/,aliases_ram_lowmem.s

@@ -89,7 +89,7 @@
 	.label C3PO      = $94  //          flag - is BSOUR content valid
 	.label BSOUR     = $95  //          serial bus buffered output byte
 	.label SYNO      = $96  //          -- NOT IMPLEMENTED --
-	.label XSAV      = $97  //          -- NOT IMPLEMENTED --
+	.label XSAV      = $97  //          temporary register storage for ASCII related routines [!] usage details might differ
 	.label LDTND     = $98  //          number of entries in LAT / FAT / SAT tables
 	.label DFLTN     = $99  //          default input device
 	.label DFLTO     = $9A  //          default output device

c64/kernal/iostack/f157.chrin.s

@@ -8,8 +8,6 @@
 // CPU registers that has to be preserved (see [RG64]): .Y
 //
 
-// XXX keyboard part currently does not preserve register Y, to be fixed!
-
 // Reads a byte of input, unless from keyboard.
 // If from keyboard, then it gets a whole line of input, and returns the first char.
 // Repeated calls after that read out the successive bytes of the line of input.

c64/kernal/keyboard/chrin_keyboard.s

@@ -7,7 +7,10 @@
 chrin_keyboard:
 
 	// Save .X
-	phx_trash_a
+	stx XSAV
+
+	// Save .Y
+	phy_trash_a
 
 chrin_repeat:
 
@@ -35,7 +38,8 @@ empty_line:
 	// (and don't forget to actually print the carriage return, so that
 	// the cursor advances and screen scrolls as required)
 
-	plx_trash_a
+	ply_trash_a
+	ldx XSAV
 	clc
 	lda #$0d
 	rts
@@ -47,8 +51,11 @@ not_end_of_input:
 	// Return next byte of waiting
 	tay
 chrin_keyboard_return_byte:
-	plx_trash_a
 	lda (LXSP),y
+	tax
+	ply_trash_a
+	txa
+	ldx XSAV
 	jsr screen_code_to_petscii
 	clc
 	rts