; XMODEM/CRC Sender/Receiver for the 65C02
;
; By Daryl Rictor Aug 2002
;
; A simple file transfer program to allow transfers between the SBC and a 
; console device utilizing the x-modem/CRC transfer protocol.  Requires 
; ~1200 bytes of either RAM or ROM, 132 bytes of RAM for the receive buffer,
; and 12 bytes of zero page RAM for variable storage.
;
;**************************************************************************
; This implementation of XMODEM/CRC does NOT conform strictly to the 
; XMODEM protocol standard in that it (1) does not accurately time character
; reception or (2) fall back to the Checksum mode.

; (1) For timing, it uses a crude timing loop to provide approximate
; delays.  These have been calibrated against a 1MHz CPU clock.  I have
; found that CPU clock speed of up to 5MHz also work but may not in
; every case.  Windows HyperTerminal worked quite well at both speeds!
;
; (2) Most modern terminal programs support XMODEM/CRC which can detect a
; wider range of transmission errors so the fallback to the simple checksum
; calculation was not implemented to save space.
;**************************************************************************
;
; Files transferred via XMODEM-CRC will have the load address contained in
; the first two bytes in little-endian format:  
;  FIRST BLOCK
;     offset(0) = lo(load start address),
;     offset(1) = hi(load start address)
;     offset(2) = data byte (0)
;     offset(n) = data byte (n-2)
;
; Subsequent blocks
;     offset(n) = data byte (n)
;
; One note, XMODEM send 128 byte blocks.  If the block of memory that
; you wish to save is smaller than the 128 byte block boundary, then
; the last block will be padded with zeros.  Upon reloading, the
; data will be written back to the original location.  In addition, the
; padded zeros WILL also be written into RAM, which could overwrite other
; data.   
;
;-------------------------- The Code ----------------------------
;
; zero page variables (adjust these to suit your needs)
;
;
lastblk		=	$35		; flag for last block
blkno		=	$36		; block number 
errcnt		=	$37		; error counter 10 is the limit
bflag		=	$37		; block flag 

crc		=	$38		; CRC lo byte  (two byte variable)
crch		=	$39		; CRC hi byte  

ptr		=	$3a		; data pointer (two byte variable)
ptrh		=	$3b		;   "    "

eofp		=	$3c		; end of file address pointer (2 bytes)
eofph		=	$3d		;  "	"	"	"

retry		=	$3e		; retry counter 
retry2		=	$3f		; 2nd counter

;
;
; non-zero page variables and buffers
;
;
Rbuff		=	$0300      	; temp 132 byte receive buffer 
					;(place anywhere, page aligned)
;
;
;  tables and constants
;
;
; The crclo & crchi labels are used to point to a lookup table to calculate
; the CRC for the 128 byte data blocks.  There are two implementations of these
; tables.  One is to use the tables included (defined towards the end of this
; file) and the other is to build them at run-time.  If building at run-time,
; then these two labels will need to be un-commented and declared in RAM.
;
;crclo		=	$7D00      	; Two 256-byte tables for quick lookup
;crchi		= 	$7E00      	; (should be page-aligned for speed)
;
;
;
; XMODEM Control Character Constants
SOH		=	$01		; start block
EOT		=	$04		; end of text marker
ACK		=	$06		; good block acknowledged
NAK		=	$15		; bad block acknowledged
CAN		=	$18		; cancel (not standard, not supported)
CR		=	$0d		; carriage return
LF		=	$0a		; line feed
ESC		=	$1b		; ESC to exit

;
;^^^^^^^^^^^^^^^^^^^^^^ Start of Program ^^^^^^^^^^^^^^^^^^^^^^
;
; Xmodem/CRC transfer routines
; By Daryl Rictor, August 8, 2002
;
; v1.0  released on Aug 8, 2002.
;
;
		*= 	$FA00		; Start of program (adjust to your needs)
;
; Enter this routine with the beginning address stored in the zero page address
; pointed to by ptr & ptrh and the ending address stored in the zero page address
; pointed to by eofp & eofph.
;
;
		jmp	XmodemRcv	; quick jmp table
XModemSend	jsr	PrintMsg	; send prompt and info
		lda	#$00		;
		sta	errcnt		; error counter set to 0
		sta	lastblk		; set flag to false
		lda	#$01		;
		sta	blkno		; set block # to 1
Wait4CRC	lda	#$ff		; 3 seconds
		sta	retry2		;
		jsr	GetByte		;
		bcc	Wait4CRC	; wait for something to come in...
		cmp	#"C"		; is it the "C" to start a CRC xfer?
		beq	SetstAddr	; yes
		cmp	#ESC		; is it a cancel? <Esc> Key
		bne	Wait4CRC	; No, wait for another character
		jmp	PrtAbort	; Print abort msg and exit
SetstAddr	ldy	#$00		; init data block offset to 0
		ldx	#$04		; preload X to Receive buffer
		lda	#$01		; manually load blk number	
		sta	Rbuff		; into 1st byte
		lda	#$FE		; load 1's comp of block #	
		sta	Rbuff+1		; into 2nd byte
		lda	ptr		; load low byte of start address		
		sta	Rbuff+2		; into 3rd byte	
		lda	ptrh		; load hi byte of start address		
		sta	Rbuff+3		; into 4th byte
		bra	Ldbuff1		; jump into buffer load routine

LdBuffer	lda	Lastblk		; Was the last block sent?
		beq	LdBuff0		; no, send the next one	
		jmp 	Done		; yes, we're done
LdBuff0		ldx	#$02		; init pointers
		ldy	#$00		;
		inc	Blkno		; inc block counter
		lda	Blkno		; 
		sta	Rbuff		; save in 1st byte of buffer
		eor	#$FF		; 
		sta	Rbuff+1		; save 1's comp of blkno next

LdBuff1		lda	(ptr),y		; save 128 bytes of data
		sta	Rbuff,x		;
LdBuff2		sec			; 
		lda	eofp		;
		sbc	ptr		; Are we at the last address?
		bne	LdBuff4		; no, inc pointer and continue
		lda	eofph		;
		sbc	ptrh		;
		bne	LdBuff4		; 
		inc	LastBlk		; Yes, Set last byte flag
LdBuff3		inx			;
		cpx	#$82		; Are we at the end of the 128 byte block?
		beq	SCalcCRC	; Yes, calc CRC
		lda	#$00		; Fill rest of 128 bytes with $00
		sta	Rbuff,x		;
		beq	LdBuff3		; Branch always

LdBuff4		inc	ptr		; Inc address pointer
		bne	LdBuff5		;
		inc	ptrh		;
LdBuff5		inx			;
		cpx	#$82		; last byte in block?
		bne	LdBuff1		; no, get the next
SCalcCRC	jsr 	CalcCRC
		lda	crch		; save Hi byte of CRC to buffer
		sta	Rbuff,y		;
		iny			;
		lda	crc		; save lo byte of CRC to buffer
		sta	Rbuff,y		;
Resend		ldx	#$00		;
		lda	#SOH
		jsr	Put_chr		; send SOH
SendBlk		lda	Rbuff,x		; Send 132 bytes in buffer to the console
		jsr	Put_chr		;
		inx			;
		cpx	#$84		; last byte?
		bne	SendBlk		; no, get next
		lda	#$FF		; yes, set 3 second delay 
		sta	retry2		; and
		jsr	GetByte		; Wait for Ack/Nack
		bcc	Seterror	; No chr received after 3 seconds, resend
		cmp	#ACK		; Chr received... is it:
		beq	LdBuffer	; ACK, send next block
		cmp	#NAK		; 
		beq	Seterror	; NAK, inc errors and resend
		cmp	#ESC		;
		beq	PrtAbort	; Esc pressed to abort
					; fall through to error counter
Seterror	inc	errcnt		; Inc error counter
		lda	errcnt		; 
		cmp	#$0A		; are there 10 errors? (Xmodem spec for failure)
		bne	Resend		; no, resend block
PrtAbort	jsr	Flush		; yes, too many errors, flush buffer,
		jmp	Print_Err	; print error msg and exit
Done		Jmp	Print_Good	; All Done..Print msg and exit
;
;
;

XModemRcv	jsr	PrintMsg	; send prompt and info
		lda	#$01
		sta	blkno		; set block # to 1
		sta	bflag		; set flag to get address from block 1
StartCrc	lda	#"C"		; "C" start with CRC mode
		jsr	Put_Chr		; send it
		lda	#$FF	
		sta	retry2		; set loop counter for ~3 sec delay
		lda	#$00
               	sta	crc
		sta	crch		; init CRC value	
		jsr	GetByte		; wait for input
               	bcs	GotByte		; byte received, process it
		bcc	StartCrc	; resend "C"

StartBlk	lda	#$FF		; 
		sta	retry2		; set loop counter for ~3 sec delay
		jsr	GetByte		; get first byte of block
		bcc	StartBlk	; timed out, keep waiting...
GotByte		cmp	#ESC		; quitting?
                bne	GotByte1	; no
;		lda	#$FE		; Error code in "A" of desired
                brk			; YES - do BRK or change to RTS if desired
GotByte1        cmp	#SOH		; start of block?
		beq	BegBlk		; yes
		cmp	#EOT		;
		bne	BadCrc		; Not SOH or EOT, so flush buffer & send NAK	
		jmp	RDone		; EOT - all done!
BegBlk		ldx	#$00
GetBlk		lda	#$ff		; 3 sec window to receive characters
		sta 	retry2		;
GetBlk1		jsr	GetByte		; get next character
		bcc	BadCrc		; chr rcv error, flush and send NAK
GetBlk2		sta	Rbuff,x		; good char, save it in the rcv buffer
		inx			; inc buffer pointer	
		cpx	#$84		; <01> <FE> <128 bytes> <CRCH> <CRCL>
		bne	GetBlk		; get 132 characters
		ldx	#$00		;
		lda	Rbuff,x		; get block # from buffer
		cmp	blkno		; compare to expected block #	
		beq	GoodBlk1	; matched!
		jsr	Print_Err	; Unexpected block number - abort	
		jsr	Flush		; mismatched - flush buffer and then do BRK
;		lda	#$FD		; put error code in "A" if desired
		brk			; unexpected block # - fatal error - BRK or RTS
GoodBlk1	eor	#$ff		; 1's comp of block #
		inx			;
		cmp	Rbuff,x		; compare with expected 1's comp of block #
		beq	GoodBlk2 	; matched!
		jsr	Print_Err	; Unexpected block number - abort	
		jsr 	Flush		; mismatched - flush buffer and then do BRK
;		lda	#$FC		; put error code in "A" if desired
		brk			; bad 1's comp of block#	
GoodBlk2	jsr	CalcCRC		; calc CRC
		lda	Rbuff,y		; get hi CRC from buffer
		cmp	crch		; compare to calculated hi CRC
		bne	BadCrc		; bad crc, send NAK
		iny			;
		lda	Rbuff,y		; get lo CRC from buffer
		cmp	crc		; compare to calculated lo CRC
		beq	GoodCrc		; good CRC
BadCrc		jsr	Flush		; flush the input port
		lda	#NAK		;
		jsr	Put_Chr		; send NAK to resend block
		jmp	StartBlk	; start over, get the block again			
GoodCrc		ldx	#$02		;
		lda	blkno		; get the block number
		cmp	#$01		; 1st block?
		bne	CopyBlk		; no, copy all 128 bytes
		lda	bflag		; is it really block 1, not block 257, 513 etc.
		beq	CopyBlk		; no, copy all 128 bytes
		lda	Rbuff,x		; get target address from 1st 2 bytes of blk 1
		sta	ptr		; save lo address
		inx			;
		lda	Rbuff,x		; get hi address
		sta	ptr+1		; save it
		inx			; point to first byte of data
		dec	bflag		; set the flag so we won't get another address		
CopyBlk		ldy	#$00		; set offset to zero
CopyBlk3	lda	Rbuff,x		; get data byte from buffer
		sta	(ptr),y		; save to target
		inc	ptr		; point to next address
		bne	CopyBlk4	; did it step over page boundary?
		inc	ptr+1		; adjust high address for page crossing
CopyBlk4	inx			; point to next data byte
		cpx	#$82		; is it the last byte
		bne	CopyBlk3	; no, get the next one
IncBlk		inc	blkno		; done.  Inc the block #
		lda	#ACK		; send ACK
		jsr	Put_Chr		;
		jmp	StartBlk	; get next block

RDone		lda	#ACK		; last block, send ACK and exit.
		jsr	Put_Chr		;
		jsr	Flush		; get leftover characters, if any
		jsr	Print_Good	;
		rts			;
;
;^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
;======================================================================
;  I/O Device Specific Routines
;
;  Two routines are used to communicate with the I/O device.
;
; "Get_Chr" routine will scan the input port for a character.  It will
; return without waiting with the Carry flag CLEAR if no character is
; present or return with the Carry flag SET and the character in the "A"
; register if one was present.
;
; "Put_Chr" routine will write one byte to the output port.  Its alright
; if this routine waits for the port to be ready.  its assumed that the 
; character was send upon return from this routine.
;
; Here is an example of the routines used for a standard 6551 ACIA.
; You would call the ACIA_Init prior to running the xmodem transfer
; routine.
;
ACIA_Data	=	$7F70		; Adjust these addresses to point 
ACIA_Status	=	$7F71		; to YOUR 6551!
ACIA_Command	=	$7F72		;
ACIA_Control	=	$7F73		;

ACIA_Init      	lda	#$1F           	; 19.2K/8/1
               	sta	ACIA_Control   	; control reg 
               	lda	#$0B           	; N parity/echo off/rx int off/ dtr active low
               	sta	ACIA_Command   	; command reg 
               	rts                  	; done
;
; input chr from ACIA (no waiting)
;
Get_Chr		clc			; no chr present
               	lda	ACIA_Status     ; get Serial port status
               	and	#$08            ; mask rcvr full bit
              	beq	Get_Chr2	; if not chr, done
               	Lda	ACIA_Data       ; else get chr
	       	sec			; and set the Carry Flag
Get_Chr2    	rts			; done
;
; output to OutPut Port
;
Put_Chr	   	PHA                     ; save registers
Put_Chr1     	lda	ACIA_Status     ; serial port status
              	and	#$10            ; is tx buffer empty
               	beq	Put_Chr1        ; no, go back and test it again
               	PLA                     ; yes, get chr to send
               	sta	ACIA_Data       ; put character to Port
               	RTS                     ; done
;=========================================================================
;
; subroutines
;
;
;
GetByte		lda	#$00		; wait for chr input and cycle timing loop
		sta	retry		; set low value of timing loop
StartCrcLp	jsr	Get_chr		; get chr from serial port, don't wait 
		bcs	GetByte1	; got one, so exit
		dec	retry		; no character received, so dec counter
		bne	StartCrcLp	;
		dec	retry2		; dec hi byte of counter
		bne	StartCrcLp	; look for character again
		clc			; if loop times out, CLC, else SEC and return
GetByte1	rts			; with character in "A"
;
Flush		lda	#$70		; flush receive buffer
		sta	retry2		; flush until empty for ~1 sec.
Flush1		jsr	GetByte		; read the port
		bcs	Flush		; if chr recvd, wait for another
		rts			; else done
;
PrintMsg	ldx	#$00		; PRINT starting message
PrtMsg1		lda   	Msg,x		
		beq	PrtMsg2			
		jsr	Put_Chr
		inx
		bne	PrtMsg1
PrtMsg2		rts
Msg		.byte	"Begin XMODEM/CRC transfer.  Press <Esc> to abort..."
		.BYTE  	CR, LF
               	.byte   0
;
Print_Err	ldx	#$00		; PRINT Error message
PrtErr1		lda   	ErrMsg,x
		beq	PrtErr2
		jsr	Put_Chr
		inx
		bne	PrtErr1
PrtErr2		rts
ErrMsg		.byte 	"Transfer Error!"
		.BYTE  	CR, LF
                .byte   0
;
Print_Good	ldx	#$00		; PRINT Good Transfer message
Prtgood1	lda   	GoodMsg,x
		beq	Prtgood2
		jsr	Put_Chr
		inx
		bne	Prtgood1
Prtgood2	rts
GoodMsg		.byte	EOT,CR,LF,EOT,CR,LF,EOT,CR,LF,CR,LF
		.byte 	"Transfer Successful!"
		.BYTE  	CR, LF
                .byte   0


;
;
;=========================================================================
;
;
;  CRC subroutines 
;
;
CalcCRC		lda	#$00		; yes, calculate the CRC for the 128 bytes
		sta	crc		;
		sta	crch		;
		ldy	#$02		;
CalcCRC1	lda	Rbuff,y		;
		eor 	crc+1 		; Quick CRC computation with lookup tables
       		tax		 	; updates the two bytes at crc & crc+1
       		lda 	crc		; with the byte send in the "A" register
       		eor 	CRCHI,X
       		sta 	crc+1
      	 	lda 	CRCLO,X
       		sta 	crc
		iny			;
		cpy	#$82		; done yet?
		bne	CalcCRC1	; no, get next
		rts			; y=82 on exit
;
; Alternate solution is to build the two lookup tables at run-time.  This might
; be desirable if the program is running from ram to reduce binary upload time.
; The following code generates the data for the lookup tables.  You would need to
; un-comment the variable declarations for crclo & crchi in the Tables and Constants
; section above and call this routine to build the tables before calling the
; "xmodem" routine.
;
;MAKECRCTABLE
;		ldx 	#$00
;		LDA	#$00
;zeroloop	sta 	crclo,x
;		sta 	crchi,x
;		inx
;		bne	zeroloop
;		ldx	#$00
;fetch		txa
;		eor	crchi,x
;		sta	crchi,x
;		ldy	#$08
;fetch1		asl	crclo,x
;		rol	crchi,x
;		bcc	fetch2
;		lda	crchi,x
;		eor	#$10
;		sta	crchi,x
;		lda	crclo,x
;		eor	#$21
;		sta	crclo,x
;fetch2		dey
;		bne	fetch1
;		inx
;		bne	fetch
;		rts
;
; The following tables are used to calculate the CRC for the 128 bytes
; in the xmodem data blocks.  You can use these tables if you plan to 
; store this program in ROM.  If you choose to build them at run-time, 
; then just delete them and define the two labels: crclo & crchi.
;
; low byte CRC lookup table (should be page aligned)
		*= $FD00
crclo
 .byte $00,$21,$42,$63,$84,$A5,$C6,$E7,$08,$29,$4A,$6B,$8C,$AD,$CE,$EF
 .byte $31,$10,$73,$52,$B5,$94,$F7,$D6,$39,$18,$7B,$5A,$BD,$9C,$FF,$DE
 .byte $62,$43,$20,$01,$E6,$C7,$A4,$85,$6A,$4B,$28,$09,$EE,$CF,$AC,$8D
 .byte $53,$72,$11,$30,$D7,$F6,$95,$B4,$5B,$7A,$19,$38,$DF,$FE,$9D,$BC
 .byte $C4,$E5,$86,$A7,$40,$61,$02,$23,$CC,$ED,$8E,$AF,$48,$69,$0A,$2B
 .byte $F5,$D4,$B7,$96,$71,$50,$33,$12,$FD,$DC,$BF,$9E,$79,$58,$3B,$1A
 .byte $A6,$87,$E4,$C5,$22,$03,$60,$41,$AE,$8F,$EC,$CD,$2A,$0B,$68,$49
 .byte $97,$B6,$D5,$F4,$13,$32,$51,$70,$9F,$BE,$DD,$FC,$1B,$3A,$59,$78
 .byte $88,$A9,$CA,$EB,$0C,$2D,$4E,$6F,$80,$A1,$C2,$E3,$04,$25,$46,$67
 .byte $B9,$98,$FB,$DA,$3D,$1C,$7F,$5E,$B1,$90,$F3,$D2,$35,$14,$77,$56
 .byte $EA,$CB,$A8,$89,$6E,$4F,$2C,$0D,$E2,$C3,$A0,$81,$66,$47,$24,$05
 .byte $DB,$FA,$99,$B8,$5F,$7E,$1D,$3C,$D3,$F2,$91,$B0,$57,$76,$15,$34
 .byte $4C,$6D,$0E,$2F,$C8,$E9,$8A,$AB,$44,$65,$06,$27,$C0,$E1,$82,$A3
 .byte $7D,$5C,$3F,$1E,$F9,$D8,$BB,$9A,$75,$54,$37,$16,$F1,$D0,$B3,$92
 .byte $2E,$0F,$6C,$4D,$AA,$8B,$E8,$C9,$26,$07,$64,$45,$A2,$83,$E0,$C1
 .byte $1F,$3E,$5D,$7C,$9B,$BA,$D9,$F8,$17,$36,$55,$74,$93,$B2,$D1,$F0 

; hi byte CRC lookup table (should be page aligned)
		*= $FE00
crchi
 .byte $00,$10,$20,$30,$40,$50,$60,$70,$81,$91,$A1,$B1,$C1,$D1,$E1,$F1
 .byte $12,$02,$32,$22,$52,$42,$72,$62,$93,$83,$B3,$A3,$D3,$C3,$F3,$E3
 .byte $24,$34,$04,$14,$64,$74,$44,$54,$A5,$B5,$85,$95,$E5,$F5,$C5,$D5
 .byte $36,$26,$16,$06,$76,$66,$56,$46,$B7,$A7,$97,$87,$F7,$E7,$D7,$C7
 .byte $48,$58,$68,$78,$08,$18,$28,$38,$C9,$D9,$E9,$F9,$89,$99,$A9,$B9
 .byte $5A,$4A,$7A,$6A,$1A,$0A,$3A,$2A,$DB,$CB,$FB,$EB,$9B,$8B,$BB,$AB
 .byte $6C,$7C,$4C,$5C,$2C,$3C,$0C,$1C,$ED,$FD,$CD,$DD,$AD,$BD,$8D,$9D
 .byte $7E,$6E,$5E,$4E,$3E,$2E,$1E,$0E,$FF,$EF,$DF,$CF,$BF,$AF,$9F,$8F
 .byte $91,$81,$B1,$A1,$D1,$C1,$F1,$E1,$10,$00,$30,$20,$50,$40,$70,$60
 .byte $83,$93,$A3,$B3,$C3,$D3,$E3,$F3,$02,$12,$22,$32,$42,$52,$62,$72
 .byte $B5,$A5,$95,$85,$F5,$E5,$D5,$C5,$34,$24,$14,$04,$74,$64,$54,$44
 .byte $A7,$B7,$87,$97,$E7,$F7,$C7,$D7,$26,$36,$06,$16,$66,$76,$46,$56
 .byte $D9,$C9,$F9,$E9,$99,$89,$B9,$A9,$58,$48,$78,$68,$18,$08,$38,$28
 .byte $CB,$DB,$EB,$FB,$8B,$9B,$AB,$BB,$4A,$5A,$6A,$7A,$0A,$1A,$2A,$3A
 .byte $FD,$ED,$DD,$CD,$BD,$AD,$9D,$8D,$7C,$6C,$5C,$4C,$3C,$2C,$1C,$0C
 .byte $EF,$FF,$CF,$DF,$AF,$BF,$8F,$9F,$6E,$7E,$4E,$5E,$2E,$3E,$0E,$1E 
;
;
; End of File
;