;;
;; Official Kernal routine, described in:
;;
;; - [RG64] C64 Programmer's Reference Guide   - page 293 (RESTOR), 304 (VECTOR)
;; - [CM64] Compute's Mapping the Commodore 64 - page 237
;;
;; CPU registers that has to be preserved (see [RG64]): none
;;

restor:

	clc ;; clear carry - for writing to system table
	ldx #<vector_defaults
	ldy #>vector_defaults

	;; FALLTHROUGH

vector:

.scope

	;; Temporary storage location - checked on real C64 that this is the
	;; address originally used; after calling VECTOR and checking zero page
	;; area afterwards, the address could be found there
	.alias _caller_arr_ptr MEMUS

	;; According to 'Compute's Mapping the Commodore 64' page 237,
	;; the CBM implementation does not disable IRQs - yet, the
	;; 'C64 Programmers Reference Guide' does not contain such
	;; warning and does not mention any preparations needed, so...
	;; better safe than sorry, disable the IRQ for the duration
	;; of vector manipulation
	php
	cli
	
	;; Prepare the user data pointer - strange order to reduce risk
	;; of potential similarity to the original routine
	sty _caller_arr_ptr + 1
	stx _caller_arr_ptr + 0
	
	;; Select routine variant - store or restore vectors
	ldy #$1F
	bcc vector_restore
	
	;; FALLTHROUGH
	
vector_store:
*
	lda CINV, y
	sta (_caller_arr_ptr), y
	dey
	bpl -
	
	;; Restore status register (IRQ) before return
	plp
	rts
	
vector_restore:
*
	lda (_caller_arr_ptr), y
	sta CINV, y
	dey
	bpl -

	;; Restore status register (IRQ) before return
	plp
	rts

.scend