;Decoder module

;----------------------------------------------------------------------------

;Constantes:

.equ	FCLK	= 16000000		;Fclk, Hz
.equ	FOUT	= 125			;output frequency, kHz
.equ	BYTC	= 11			;data byte count
.equ	BITC	= 5			;data bit count
.equ	dMask	= 0b00011111		;data byte mask
.equ	sSymb	= 0b0000000111111111	;syncro symbol
.equ	sMask	= 0b0000001111111111	;syncro symbol mask

.equ	MIN1T	= 58 			;64  - 10%
.equ	NOM1T5	= 96			;64  + 1/2 * 64
.equ	MAX2T	= 141			;128 + 10%

;Decoder phases (dPhase values):

.equ	pOff	= 0			;off
.equ	pSync	= 1			;find syncronization
.equ	pData	= 2			;get data

;----------------------------------------------------------------------------

;Derivated constantes:

.equ T1DIV = (((FCLK/FOUT)/200)+5)/10	;CK/1

.if T1DIV > MAXWORD
.error "out of range constant"
.endif

;----------------------------------------------------------------------------

.DSEG	;Data segment

dBuff:	.byte	BYTC			;data buffer

;----------------------------------------------------------------------------

.CSEG	;Code segment

.equ	Decod	= PC

;----------------------------------------------------------------------------

;Interrupt Vectors:

.org	OC1Aaddr
	rjmp	FInt			;Timer1 OC vector

.org	Decod

;----------------------------------------------------------------------------

;Decoder init:

iDec:	ldi	temp,(1<<COM1A1) | (1<<COM1A0) | (1<<COM1B1)
;	ldi	temp,0
	out	TCCR1A,temp		;

	ldi	temp,(1<<WGM12) | (1<<CS10)	
	out	TCCR1B,temp		;CTC, CK/1

	ldi	temp,byte2(T1DIV-1)
	out	OCR1AH,temp		;compare register load	
	ldi	temp,byte1(T1DIV-1)
	out	OCR1AL,temp

	in	temp,TIMSK
	ori	temp,(1<<OCIE1A)
	out	TIFR,temp		;clear pending interrupts
	out	TIMSK,temp		;output compare interrupt enable

	ldi	dPhase,pSync
	clr	dSyncL
	clr	dSyncH
	ret

;----------------------------------------------------------------------------

;Decode routine:
;Input:	NowIn
;Out:	dBuff	

mDec:	stbr	Flags,NowIn
	Skip_if_Port_DecIn_0		;sample DecIn (inverted!)
	clbr	Flags,NowIn
		
	bbrs	Flags,NowIn,In1		;check for transition
In0:	bbrc	Flags,PreIn,SkipT	;no changes
	rjmp	YesTr
In1:	bbrs	Flags,PreIn,SkipT	;no changes

;Check for timer:

YesTr:	cpi	dTimer,MIN1T
	brlo	SkipT			;skip early transition

	cpi	dTimer,MAX2T
	brlo	GetSyn

	ldi	dPhase,pSync		;too late transition
	rjmp	NewTm

;Get synchronization:

GetSyn:	cpi	dPhase,pSync
	brne	GetDat

	cpi	dTimer,NOM1T5
	brsh	gets1			;dTimer > NOM1T5

	bbrc	Flags,Half,gets1	;dTimer < NOM1T5
	clbr	Flags,Half
	rjmp	NewTm
gets1:	stbr	Flags,Half
	clc
	sbrc	Flags,NowIn
	sec
	rol	dSyncL
	rol	dSyncH
	andi	dSyncL,byte1(sMask)
	andi	dSyncH,byte2(sMask)
	cpi	dSyncL,byte1(sSymb)
	brne	NewTm
	cpi	dSyncH,byte2(sSymb)
	brne	NewTm

	Port_Sync_1
	ldi	dPhase,pData
	clr	dCnt
	clr	dSyncL
	clr	dSyncH
	Port_Sync_0
	rjmp	NewTm

;Get data:

GetDat:	cpi	dTimer,NOM1T5
	brsh	getd1			;dTimer > NOM1T5

	bbrc	Flags,Half,getd1	;dTimer < NOM1T5
	clbr	Flags,Half
	rjmp	NewTm
getd1:	stbr	Flags,Half
	
	cpi	dPhase,pData+BYTC
	brsh	NewTm

	ldy	dBuff-pData
	add	YL,dPhase
	adc	YH,dPhase
	sub	YH,dPhase
	ld	temp,Y
	clc
	sbrc	Flags,NowIn
	sec
	rol	temp
	andi	temp,dMask
	st	Y,temp			;save data

	inc	dCnt
	cpi	dCnt,BITC		;bit count
	brne	NewTm
	clr	dCnt
	inc	dPhase			;new byte

NewTm:	bst	Flags,NowIn
	bld	Flags,PreIn
	clr	dTimer

SkipT:	ret

;----------------------------------------------------------------------------

;Check parity:
;Out:	C=1 if parity error

CheckP:	ldi	Cnt,BYTC-1
	ldy	dBuff

nrr:	ldi	XL,0			;check parity for rows 1..10
	ld	temp,Y+
	sbrc	temp,4
	inc	XL
	sbrc	temp,3
	inc	XL
	sbrc	temp,2
	inc	XL
	sbrc	temp,1
	inc	XL
	sbrc	temp,0
	inc	XL
	andi	XL,0x01
	brne	PErr
	dec	Cnt
	brne	nrr

	ldi	Cnt,BYTC		;check parity for col 1
	ldy	dBuff
	ldi	XL,0
nra:	ld	temp,Y+
	sbrc	temp,4
	inc	XL
	dec	Cnt
	brne	nra
	andi	XL,0x01
	brne	PErr

	ldi	Cnt,BYTC		;check parity for col 2
	ldy	dBuff
	ldi	XL,0
nrb:	ld	temp,Y+
	sbrc	temp,3
	inc	XL
	dec	Cnt
	brne	nrb
	andi	XL,0x01
	brne	PErr

	ldi	Cnt,BYTC		;check parity for col 3
	ldy	dBuff
	ldi	XL,0
nrc:	ld	temp,Y+
	sbrc	temp,2
	inc	XL
	dec	Cnt
	brne	nrc
	andi	XL,0x01
	brne	PErr

	ldi	Cnt,BYTC		;check parity for col 4
	ldy	dBuff
	ldi	XL,0
nrd:	ld	temp,Y+
	sbrc	temp,1
	inc	XL
	dec	Cnt
	brne	nrd
	andi	XL,0x01
	brne	PErr

	lds	temp,dBuff+BYTC-1	;check stop bit
	andi	temp,0x01
	brne	PErr
	clc				;clear error flag
	rjmp	POk

PErr:	sec				;set parity error flag
POk:	ret

;----------------------------------------------------------------------------

;Timer interrupt:

FInt:	in	xSreg,SREG
	push	temp

;Update Out_P and Out_N:

	Skip_if_Port_Out_P_0
	rjmp	Ph1

Ph0:
	ldi	temp,(1<<COM1A1) | (1<<COM1A0) | (1<<COM1B1)
	out	TCCR1A,temp
	rjmp	PhX

Ph1:
	ldi	temp,(1<<COM1A1) | (1<<COM1B0) | (1<<COM1B1)
	out	TCCR1A,temp
PhX:	

;Advance decoder timer:

	cpi	dTimer,MAX2T
	breq	dT0
	inc	dTimer
dT0:

;Advance wiegand rate timer:

	dec	wTimer
	brne	wT0
	ldi	temp,WRT
	mov	wTimer,temp
	stbr	Flags,wRate
wT0:

	pop	temp
	out	SREG,xSreg
	reti

;----------------------------------------------------------------------------