; Output:
; io_soundtype:
;	bit 7: 1: NAE (NST Audio Extension - BSz SID Card), 0: legacy SID Card
;	bit 6-0: 0: TED only, 1: 6581 2: 8580
; io_sidbase: SID address
;================================================
sidptr = 2

	lda #0
	sta io_soundtype
	
	ldx #<$fd40
	ldy #>$fd40
	jsr io_detsidaddr
	cmp #$ff
	beq hassid
	ldx #<$fe80
	ldy #>$fe80
	jsr io_detsidaddr
	cmp #$ff
	bne nosid
hassid
	inc io_soundtype
	jsr detsidtp
	jsr detnae
	; Do whatever you need with SID
	rts
nosid
	; Do whatever you need without SID
	rts

;=======================================
;  In: XR: SID address low
;      YR: SID address high
; Out: AC: 0: not found $ff: found
;=======================================

io_detsidaddr	
	lda #0
	sta io_sidbase
	sta io_sidbase+1
	
	stx sidptr
	sty sidptr+1
	
	ldy #24
-	sta (sidptr),y
	dey
	bpl -
	
	ldy #25
	lda (sidptr),y
	iny
	and (sidptr),y
	rts

; Detect SID chip type
; original version from Reflex Math demo
;=======================================
	
detsidtp
	lda #1
	sta io_soundtype
	
;Set a low frequency for Oscillator
; (Voice 3) #$0200 which is somewhere
; between B-0 and C-1, according to demo
	
	ldy #15
	lda #$02
	sta (sidptr),y

;Set Sawtooth and Triangle waveforms for
;voice 3 and start release of ADSR
	
	ldy #18
	lda #%00110000
	sta (sidptr),y
	
;Check if output of voice 3 ever goes
;higher than $80. It's only possible on
;new SID chip (8580) and never on the
;old one (6581)
	
	ldy #0
	ldx #0
	sty ystore
loop2	ldy #27
	lda (sidptr),y
	bmi newsid
	dex
	bne loop2
	ldy ystore
	dey
	sty ystore
	bne loop2
	beq oldsid
newsid
	inc io_soundtype
oldsid
	rts

;=======================================
; Detect NST SIDCard
;=======================================

detnae
	lda #%11100000
	sta nae_control+13
	ldx #0
-	lda nae_control+15
	cmp nae_control+15
	bne +
	dex
	bne -
	and #%11100000
	cmp #%11100000
	beq +		; Legacy SID-Card
	lda nae_control+15
	beq +		; VICE 
	lda io_soundtype
	ora #%10000000
-	sta io_soundtype
+	rts

io_soundtype	.byte 0
io_sidbase	.word 0