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/CASSETTE HANDLER FOR RTS8 V2B			8/30/74
	VERS=	1
	XLIST	1		/COPYRIGHT ALSO GIVEN IN PARAM.PA
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/COPYRIGHT  (C)  1974,1975,1976 BY DIGITAL EQUIPMENT CORPORATION
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/THE INFORMATION IN THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE
/AND SHOULD NOT BE CONSTRUED AS A COMMITMENT BY DIGITAL EQUIPMENT
/CORPORATION.  DIGITAL EQUIPMENT CORPORATION ASSUMES NO RESPONSIBILITY
/FOR ANY ERRORS THAT MAY APPEAR IN THIS DOCUMENT.
/
/THE SOFTWARE DESCRIBED IN THIS DOCUMENT IS FURNISHED TO THE PURCHASER
/UNDER A LICENSE FOR USE ON A SINGLE COMPUTER SYSTEM AND CAN BE COPIED
/(WITH INCLUSION OF DIGITAL'S COPYRIGHT NOTICE) ONLY FOR USE IN SUCH
/SYSTEM, EXCEPT AS MAY OTHERWISE BE PROVIDED IN WRITING BY DIGITAL.
/
/DIGITAL EQUIPMENT CORPORATION ASSUMES NO RESPONSIBILITY FOR THE USE
/OR RELIABILITY OF ITS SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY
/DIGITAL.
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	XLIST	0	/LIST TASK
	KCLR=6700	/CLEAR ALL
			/CLEAR STATUS A AND B REGISTERS
	KSDR=6701	/SKIP ON DATA FLAG
	KSEN=6702	/SKIP ON ERROR
	KSBF=6703	/SKIP ON READY FLAG
	KLSA=6704	/LOAD STATUS A FROM AC 4-11
			/CLEAR AC, THEN
			/LOAD 8 BIT COMPLEMENT OF STATUS A
			/BACK INTO AC
	KSAF=6705	/SKIP ON ANY FLAG OR ERROR
	KGOA=6706	/ASSERT THE CONTENTS OF STATUS A,
			/TRANSFER DATA IF READ OR WRITE
	KRSB=6707	/READ STATUS B INTO AC 4-11
	INT=1

	INIWT=0
	TASK=CSA
	CUR=10
	FIELD	CUR%10

/FORMAT OF MESSAGE IS:
/
/MSG,	ZBLOCK 3
/	WORD 1 = UNIT
/		BITS 9-11 = UNIT
/		BIT  0    = 0 = UTILITIES CALL
/			  = 1 = HANDLER CALL
/	WORD 2 = FUNCTION
/		FOR HANDLER BIT 0 = 1 = WRITE, = 0 = READ
/			    BITS 6-8 = FIELD OF BUFFER
/			    BIT 11 = 1 = DO NOT STORE DATA (ON READ ONLY)
/		FOR UTILITY UTIL WORD
/			10 = REWIND
/			30 = BACKSPACE FILE GAP
/			40 = WRITE FILE GAP
/			50 = BACKSPACE BLOCK GAP
/			70 = SKIP TO FILE GAP
/	WORD 3
/		FOR UTILITY = STATUS RETURN
/		FOR HANDLER = BUFFER ADDRESS
/	WORD 4
/		FOR HANDLER = RECORD SIZE
/		FOR UTIL  UNUSED
/	WORD 5
/		FOR HANDLER = STATUS RETURN
/		FOR UTIL  UNUSED

/STATUS B BITS:
/	4=CRC/BLK ERROR
/	5=TIMING
/	6=EOT/BOT
/	7=EOF
/	8=DRIVE EMPTY
/	9=RW
/	10=WRITE LOCK OUT
/	11=READY
	*3600
FIXDVC,	0
	RAR		/MOVE UNIT TO LINK; DEVICE TO AC
	AND	(3	/MASK OFF DEVICE CODE
	DCA	DVC	/SAVE DEVICE CODE
	SZL
	TAD	(100
	DCA	ABUNIT	/SET UNIT IN BIT 5
	TAD	DVC
	CLL RTL
	RAL		
	DCA	DVC	/MOVE TO BITS 6-8
	TAD	(IOTBL
	DCA	IOTPTR
IOTLOOP,TAD I	IOTPTR
	SNA		/END OF TABLE?
	JMP	CHECKR	/YES
	DCA	TMP
	TAD I	TMP
	AND	(7707	/MASK OUT OLD DVC
	TAD	DVC	/INSERT NEW ONE
	DCA I	TMP	/REPLACE
	ISZ	IOTPTR	/POINT TO NEXT ONE
	JMP	IOTLOOP

TMP,	0
DVC,	0		/DEVICE CODE
IOTPTR,	0
CHECKR,	JMS I	(CLEAR
	TAD	(200
	JMS	LOADA	/SELECT DRIVE
	JMS I	(CHECKB
	AND	(7735	/IGNORE EOT/BOT FLAG + WLO
	TAD	(-1
	SZA	CLA
	JMP I	(SELERR	/NOT READY
	JMP I	FIXDVC


READX,	JMS I	(CHK
	AND	L374
	SZA
	JMP	ERRX
IOT6C,	KGOA		/GET CHAR JUST READ
	DCA	BYTE
	ISZ	BKNT
	SKP
	JMP	RWCRC
	TAD	BYTE
BFLD,	HLT
DMPFLG,	DCA I	BPTR	/ZEROED IF BIT 11=1 ON READ
	CLA
	ISZ	BPTR
	CDF	CUR
L374,	374
	JMS I	(IDISP
	JMP	READX

LOADA,	0
	TAD	ABUNIT
IOT4,	KLSA
	CLA
	JMP I	LOADA

ABUNIT,	0

RWCRC,	TAD	(260+INT	/ENABLE, ENABLE INTER, READ CRC
	JMS	LOADA
	JMS I	(GO
	JMS I	(IDISP
	JMS I	(CHK
CRCMN,	JMS I	(GO
	JMS I	(IDISP
	JMS I	(CHECKB
	AND	(7775	/IGNORE WLO
	TAD	(-1
ERRX,	SNA	CLA	/ERRORS?
	JMP	ERRR+1	/NO - CLEAN BILL OF HEALTH
E3,	ISZ I	(ERKNT	/TRY 3 TIMES
	JMP I 	(ERRCOV	/RETRY
ERRR,	STA		/ERROR WHILE READING CRC
	JMS I	(CLEAR
	JMP I	(FINAL
WRITEX,	JMP	READX
WRITEL,	JMS I	(CHK
	CLL RTR
	SZL
	JMP	ERRR	/WLO ON WRITE OP NOT WORTH RETRYING
	SZA CLA
	JMP	E3
	ISZ	BKNT
	SKP
	JMP	WCRC
BFIELD,	HLT
	ISZ	BPTR
	70
	TAD I	BPTR
	JMS I	(GO
	JMS I	(IDISP
	JMP	WRITEL


WCRC,	TAD	(260+INT
	JMS	LOADA
	JMP	CRCMN
BKNT,	0		/NUMBER OF CHARS EXPECTED
BPTR,	0		/NEXT LOCATION IN BUFFER TO STORE INTO
BYTE,	0		/TEMPORARILY HOLDS BYTE FOUND
	PAGE
IOTBL,	IOT0
	IOT1
	IOT4
	IOT5
	IOT6
	IOT6C
	IOT7
	ERRCOV
	0

UTIL,	RAR
	DCA I	(UNIT
	DCA	REWSW
	JMS I	(GET	/FUNCTION WORD
	TAD	(-10
	SNA
	ISZ	REWSW
	TAD	(210+INT
	DCA	TEMPFN
	TAD I	(UNIT
	IOF
	JMS I	(FIXDVC	/FIX DEVICE CODE
	TAD	(UT
	DCA	IDISP	/SET RETURN ADDRESS
	TAD	TEMPFN
	JMS I	(LOADA
	JMS	GO	/INITIATE UTIL
	JMP I	(COMDN
UT,	JMS	CHECKB	/LOOK AT STATUS B
	AND	(50	/CHECK FOR CL, EMPTY, OR WLO
			/GIVE NO ERROR ON WLO ************
			/BAD FOR WRGAP
	SNA
	JMP	OK	/NO ERRORS
	TAD	(-40
	SZA	CLA
	JMP	NOTOK	/ERROR NOT CL
	TAD	REWSW
	SNA	CLA	/CL OK IF DID REWIND
NOTOK,	STA	
OK,	JMS	CLEAR
	JMP	FINAL

TEMPFN,	0
REWSW,	0		/1 MEANS OPERATION IS REWIND
CHECKB,	0
IOT7,	KRSB		/READ STATUS B INTO AC 4-11
	DCA	BSTATE	/SAVE STATUS B
	TAD	BSTATE
	JMP I	CHECKB

CLEAR,	0
	DCA	ERRIND	/-1 MEANS  ERROR
IOT0,	KCLR		/CLEAR STATUS A AND B
	JMP I	CLEAR

GO,	0
IOT6,	KGOA		/ASSERT CONTENTS OF STATUS A
	CLA
	JMP I	GO

CHK,	0
	JMS	CHECKB
	AND	(376
IOT1,	KSDR
	SKP		/DATA FLAG NOT UP -
	JMP I	CHK
	TAD	(-20
	SNA	CLA	/IS IT END OF FILE?
	JMP I	(ERRR	/YES, ERROR - BUT DON'T RETRY
	TAD	BSTATE
	JMP I	CHK

BSTATE,	0		/STATUS OF REGISTER B
ERRIND,	0
FINAL,	TAD	(DONEFG
	JMS 	IDISP	/FINAL PDS SETS EVENT FLAG
	HLT		/DEBUG ONLY. SHOULD NEVER GET HERE

IDISP,	HLT
	CIF	0
	POSTDS

CASINT,	ZBLOCK 2
IOT5,	KSAF
	JMP I	CASINT
	CDF CIF CUR
	JMP I	IDISP

ERRCOV,	KCLR
	TAD	(250+INT
	JMS I	(LOADA
	JMS 	GO	/BACKSPACE BLOCK
	JMS I	(IDISP	/WAIT
	JMS 	CHECKB
	AND	(374	/KILL WRITE-LOCK BIT
	SZA	CLA
	JMP I 	(ERRR
	JMS I	(SETUP	/RE-SET UP OPERATION
	JMP	IDISP+1	/FAKE A JMS
	PAGE
/	*ORG3

START,	CAL
DONEFG,	SKPINS
	CASINT
LOOP,	CAL
	RECEIV
ADDR,	0
	DCA	FLD
	DCA	RW
	TAD	DCASET
	DCA I	(DMPFLG
	AC7775
	TAD	ADDR
	DCA	MEVFLG
	ISZ	DONEFG
	JMS	GET
	ISZ	ADDR
	CLL	RAL
	SNL
	JMP I	(UTIL
	RAR
	DCA	UNIT
	JMS	GET
	AND	P70	/ISOLATE FIELD OF BUFFER
	TAD	(CDF
	DCA	WCDF
	JMS 	GET	/RETRIEVE FUNCTION CONTROL WORD
	RAL		/READ/WRITE BIT TO LINK
	SNL
	JMP	READ11	/A READ OP
	CLA	RAL
RANDW,	DCA	RW	/RW=1 IF WRITE
	ISZ	ADDR
	JMS	GET
	DCA	BUFFER	/SAVE IT
	ISZ	ADDR
	JMS	GET
	CDF	CUR
	DCA 	BSIZE	/RECORD SIZE
	TAD	UNIT	
	IOF
	JMS I	(FIXDVC
	TAD	WCDF
	DCA I	(BFIELD
	TAD	WCDF
	DCA I	(BFLD
	STA CLL RTL	/TAD (-3
	DCA	ERKNT
	JMS	SETUP	/SET UP READ OR WRITE
COMDN,	ION
	NOP
	CAL
	WAITE
	DONEFG
RTNSTS,	ISZ	ADDR
	TAD I	(ERRIND
	AND I	(BSTATE
	JMS	CDFMSG
	DCA I	ADDR
	CDF	CUR
	TAD	FLD
	DCA	PFLD
	TAD	MEVFLG
	CAL
	POST
PFLD,	0
	JMP	LOOP

GET,	0	
	JMS	CDFMSG
	TAD I	ADDR
	CDF	CUR
	JMP I	GET

CDFMSG,	0
FLD,	0
	JMP I	CDFMSG

READ11,	RTR		/BIT 11 TO LINK
	SZL	CLA
	DCA I	(DMPFLG	/DON'T STORE DATA
	JMP	RANDW
DCASET,	BPTR&177+3600	/DCA I	BPTR

UNIT,	0
MEVFLG,	0
BUFFER,	0
RW,	0		/1 IF WRITE
ERKNT,	-3
P70,	70
BSIZE,	200

SELERR,	STA
	JMP	RTNSTS	/RETURN ERROR
SETUP,	0
	TAD	RW
	TAD	(WRITEX
	DCA I	(IDISP	/SET RETURN ADDRESS
	TAD	BUFFER
	DCA I	(BPTR
	TAD	BSIZE
	CMA		/WANT TO READ ONE MORE
	TAD	RW
	DCA I	(BKNT
	TAD	RW
	CLL	RTL
	RTL		/WRITE FN CODE=0
	TAD	(200+INT	/SELECT AND INTERRUPT ENABLE
	JMS I	(LOADA
WCDF,	HLT
	TAD	RW
	SZA	CLA
	TAD I	BUFFER	/=BPTR (FOR 2 LEVELS OF INDIRECT)
	CDF	CUR
	JMS I	(GO
	JMP I	SETUP

	$