/	RXCOPY  READ-WRITE SUBROUTINE
/
	*6420
/
/  READ-WRITE SUBROUTINE TO HANDLE FLOPPY DISK IN 8-BIT MODE
/  ROUTINE LIVES IN FIELD 0 TO BE CALLED FROM FIELD 10
/
/  CALLING SEQUENCE
/
/	CIF 0		/ASSUMED CDF 10, CALLED FROM FIELD 10
/	TAD	TRACK	/TRACK # INTO AC
/	JMS I	(RW
/	BITS		/4000 IF FIELD 10 BUFFER, 2 IF READ, 20 IF UNIT 1
/	OK RETURN	/CDF AND CIF TO 10
/	ERROR		/SECTOR # IN AC
/
/  READS OR WRITES A TRACK AT A TIME. TWO BUFFERS LIVE IN 20-6417
/  EACH OF FIELD 0 AND 10
/
/ USES AUTO-INCREMENT REGISTER 10 OF FIELD 0
X10=10
/
/  AN ALTERNATE ENTRY OF CONTIN (JMP NOT JMS) CAUSES THE
/  SUBROUTINE TO CONTINUE WORKING ON THE SAME TRACK ON WHICH THE
/  ERROR OCCURRED.
/
/  THREE RETRIES ARE DONE ON A SECTOR BEFORE AN ERROR IS DECLARED.
/
SDN=6755
LCD=6751
STR=6753
XDR=6752
SER=6754
FLINIT=6757
/
/
/  USE PART OF PAGE AT 6400 TO SPREAD OUT WRITE LOOP
/  FOR A LITTLE EXTRA SAFETY ON MAKING INTERLEAVE TIMING
/
WRIT1,	TAD	(-10	/8 TIMES THRU 16 BYTE > 128
	DCA	WRTCNT
ST4,	TAD I	X10	/FETCH A BYTE
	STR		/SKIP IF READY TO TRANSFER
	JMP	.-1	/NO (SHOULDN'T HIT THIS ON VT78)
	XDR		/MOVE BYTE TO SILO
	CLA		/CLEAR THE MUMBLE AC
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	TAD I	X10
	STR
	JMP	.-1
	XDR
	CLA
	ISZ	WRTCNT	/THRU WITH SILO?
	JMP	ST4	/NO
	JMP	WRIT2	/REST OF LOOP ON OTHER PAGE
/
WRTCNT,	0		/CONTROL COUNT FOR FILL SILO LOOP
/
	PAGE
/
/
/  READ-WRITE ENTRY POINT
/
/
RW,	0
	DCA	TRCKNO	/ARRIVES WITH TRACK # IN AC
	TAD I	RW	/DATA FIELD 10, FETCH CONTROL BITS
	TAD	L7100	/FLOPPY CONTROLLER IGNORES TOP 4 BITS; 100
/			/BIT IS 8 BIT MODE; CONTROL FOR UNIT, R/W, IN PLACE
	DCA	FN	/BUFFER BIT (COMPLEMENTED) ALSO STORED IN FN
	TAD	(17	/SET UP AUTO-INCR REG.
	DCA	X10
	TAD	(-32	/26 DECIMAL SECTORS PER TRACK
	DCA	SECTOR
	ISZ	RW	/POINT TO OK EXIT
	TAD	FN	/IF FIELD ZERO BUFFER, NEED TO CDF
	SPA		/SKIP ON FIELD 10 BUFFER, ALREADY SET!
	CDF 0
	RTR		/READ/WRITE BIT TO LINK
	SZL CLA		/SKIP IF WRITE
	JMP	READLP	/GO TO READ
/
/  WRITE LOOP
/
WRITLP,	CLL CLA CMA RTL	/LITERAL -3 FOR RETRY COUNT
	DCA	RETRY
WRTRY,	TAD	FN	/RETRY ERROR HERE THREE TIMES
	JMS	LDCMD
	JMP	WRIT1	/OTHER PAGE TO MOVE DATA TO SILO
WRIT2,	JMS	DOIO	/RETURN FROM OTHER PAGE TO ACCESS I/O
	ISZ	SECTOR
	JMP	WRITLP
XT1,	CDF CIF 10
	JMP I	RW
/
/  READ LOOP
/
READLP,	CLL CLA CMA RTL	/LITERAL -3 FOR RETRY COUNT
	DCA	RETRY
RDTRY,	JMS	DOIO	/COME HERE TO RETRY I/O
	TAD	FN
	JMS	LDCMD
	TAD	(-40	/32 PASSES THRU 4 BYTES MOVED
	DCA	FLEA
ST5,	STR
	JMP	.-1
	XDR
	DCA I	X10
	STR
	JMP	.-1
	XDR
	DCA I	X10
	STR
	JMP	.-1
	XDR
	DCA I	X10
	STR
	JMP	.-1
	XDR
	DCA I	X10
	ISZ	FLEA
	JMP	ST5
	ISZ	SECTOR
	JMP	READLP
	JMP	XT1
/
/  DO READ OR WRITE I/O FUNCTION
/
DOIO,	0
	TAD	FN	/SILO FUNCTION, CONVERTED TO READ-WRITE
	TAD	L7004	/BY LITERAL 4 (TOP FOUR BITS IRREL)
	JMS	LDCMD
	JMS	GETSEC	/FETCH SECTOR TO AC
	STR
	JMP	.-1
	XDR
	CLA
	TAD	TRCKNO
	STR
	JMP	.-1
	XDR
	CLA
	TAD	L7530	/UNIT 1, 8-BIT NO-OP (TOP 4 BITS IGNORED)
	JMS	LDCMD
	JMP I	DOIO
/
/  LOAD COMMAND REGISTER
/
FLEA=.
LDCMD,	0
	SDN		/SKIP ON DONE
	JMP	.-1
	LCD		/LOAD COMMAND
	SER		/SKIP ON ERROR
	JMP I	LDCMD
	ISZ	RETRY	/TRIED THREE TIMES YET
	JMP	KEEPON	/NO, KEEP ON TRYING
	JMS	GETSEC	/RETURN SECTOR IN AC
	ISZ	RW	/ON ERROR, RETURN ONE FURTHER DOWN
	JMP	XT1	/EXIT TO CALLER WITH SECTOR # IN AC
/
/  ENTRY TO CONTINUE AFTER ERROR
/
CONTIN,	STA		/BACK UP EXIT TO GOOD EXIT
	TAD	RW
	DCA	RW
	TAD	FN	/SET DATA FIELD TO 0 IF NECESSARY
	SPA CLA		/ALREADY CDF TO 10, SKIP IF OK
	CDF 0		/NO, SO SET TO 0
	JMP I	LDCMD	/PRETEND OPERATION OK, SO RETURN THRU LDCMD!
/
KEEPON,	FLINIT		/DO A RECAL TO SHAKE IT UP
	TAD	FN	/RETRYING READ OR WRITE
	RTR		/R/W BIT TO LINK
	SZL CLA		/SKIP ON WRITE
	JMP	RDTRY	/RETRY A READ
	TAD	(-200	/BACK UP AUTO INCR TO REFILL SILO FOR WRITE
	TAD	X10	/SINCE THE FLINIT CLEARED SILO
	DCA	X10
	JMP	WRTRY	/SO GO RETRY WRITE
/
/  CONVERT COUNT TO SECTOR
/
GETSEC,	0
	TAD	SECTOR	/CONVERT -32 TO -1 TO INTERLEAVED SECTOR
	TAD	(15
L7100,	CLL		/100 BIT SETS 8-BIT MODE, AS LITERAL
L7530,	SPA SZL		/SZL JUST TO MAKE CORRECT LITERAL, NO-OP WAIT
	TAD	(15
L7004,	RAL		/CONVERTS SILO OPERATION TO READ-WRITE, AS LITERAL
	JMP I	GETSEC
/
/
/
TRCKNO,	0		/TRACK NUMBER, INVARIANT THRU CALL
SECTOR,	0		/COUNTS -32 UP TO 0; 26 DECIMAL SECTORS PER TRACK
FN,	0		/FUNCTION BITS: ALWAYS 100 FOR 8BIT MODE
/			/20 IF UNIT 1
/			/2 IF READ OPERATION (2 IS SILO FETCH; 0 SILO FILL)
/			/MINUS WORD IF BUFFER IN FIELD 0, PLUS IF FIELD 10
/			/CONTROLLER IGNORES TOP 4 BITS OF WORD
RETRY,	0		/RETRY COUNTER -3 TO 0
$