/***** MULTI8 DECTAPE EMULATOR *********
/LAST EDIT: 14-JULY-75, JV
/LAST EDIT:  4-JULY-75, ELC
/LAST EDIT: 30-JUNE-75, ELC
/LAST EDIT: 25-JUNE-75, JV+ELC
/LAST EDIT:  1-JUNE-75, JV
/LAST EDIT:  8-JANUARI-75, ELC
/LAST EDIT: 12 OKTOBER 74, ELC
/DECTAPE EMULATOR FOR BG

/NAME:	TE ("T^100+"E&3777)
/LENGTH:ONE PAGE
/FUNCTION:THIS MODULE DOES THE DECTAPE TRANSFERS FOR
/	THE OS8 BACKGROUND. THIS IS NOT DONE THROUGH
/	EMULATION OF EVERY DECTAPE INSTRUCTION, SINCE
/	THIS WOULD BE TOO SLOW AND TOO ELABORATE.
/	THE FOLLOWING SIMPLE SOLUTION IS TAKEN:
/	THERE IS A SPECIAL DECTAPE HANDLER FOR OS8
/	WHICH REPLACES THE CONVENTIONAL ONE. THIS 
/	HANDLER PICKS UP THE ARGUMENTS FOLLOWING THE
/	CALL AND COMPUTES THE DECTAPE UNIT NUMBER.
/	IT THEN ISSUES A GIANT IOT (6770) WHICH IS
/	RECOGNISED BY THE FOREGROUND.
/CONCEPT:THE MODULE IS ENTERED VIA THE SPECIAL FUNCTIONS IOT.
/	IT THEN CALLS THE DECTAPE BLOCKDRIVER FOR A
/	SEARCH-ONLY IN ORDBLOCK.
/	IN THIS TIME TE AND
/	EVEN SWAPPED BATHE RIGHT BLOCK COMES UP	IN CORE AGAIN, AND THE TRANSFER COMPLETED
/	IN A SINGLE RUSH. IN THIS TIME THE BG CANNOT BE
/	SWAPPED. (EMULATE)
/ERRORS:ERRORS ARE DEFERRED TO THE BACKGROUND BY TAKING THE
/	HANDLER ERROR-RETURN.
/USE:	TAD (BJERS
/	JMS MONITOR
/	  77
/	 BUSY RETURN	/AC UN	/AC=0:NO ERRORS
/			/HE BG ISSUES THE 'GIANT IOT' 6770
/FOLLOWED BY THE DATATRANSFER VECTOR:

/TAD (DTAFUN
/6770
/RLL.LLL.FFF.###	/READ/WRITE;LENGTH(PAGES);FIELD;UNIT
/BUFFER ADDRESS IN CORE
/BLOCK# ON DECTAPE
/HERE IS WHERE THE ERROR RETURN GOES TO
/HERE GOES THE NORMAL RETURN TO
*200
DTUAC,	"T^100+"E&3777	/TE
DTUPC,	200		/ONE PAGE;NO CONNECTS
DTIDTV,	DTDTV		/RELOCATED POINTER
DTUSTAT,0		/PNTR TO STATUS REG. OF BG

/NOTE THAT DF POINTS TO MONFLD MOST OF THE TIME
TE,	DCA DTUSTAT
	TAD DTUSTAT	/SET UP SOME POINTERS
	TAD C3
	DCA DTUPC
	AC0002
	TAD DTUPC
	DCA DTUAC
/FETCH THE POINTER TO DTV
	TAD DTUSTAT
	TAD (UDTV-1
	DCA AUTO10
	TAD I AUTO10
	AND C7770
	DCA DTFUN
	TAD I DTUAC
	AND C7		/GET UNIT NUMBER
	TAD DTFUN
	DCA DTFUN
	TAD I AUTO10
	DCA DTDTV+1	//
	TAD I AUTO10
	DCA DTBLK
IFNZRO BGMAX-1 <
/LOOK INTO THE TAPETABLE AND SEE HOW FAR WE HAVE TO GO. IF IT'S
/MORE THAN 50 BLOCKS, MAKE THE BG INACTIVE AND START A SEARCH-ONLY
/REQUEST UNTIL WE ARE QUITE NORT DISTANCE
/DO THE TRNG THE BG IN EMULATE STATAPETABLE SHOULD BE UPDA/STARTADDRESS.

	TAD DTFUN
	AND C7		/EXTRACT UNIT NUMBER
	TAD (TAPETB
	JMS DEFER	/GET CURRENT POSITION
	STL
	SNA		/IF ZERO THIS IS UNKNOWN:
	 JMP DTLONG	/THE TAPE HAS BEEN OFFLINE.
	CIA
	TAD DTBLK	/MAKE DISABSOLUTE VALUE OF DISTANAD GOES TO LINK
DTLONG, X		/X WAS USED BY DEFERLA
	 JMP DTSHRT	/LUCKY BOY, NO SWAPS TODAY
/FIRST SEARCH FOR THE DESIRED BLOCK;LENGTH=0
/STOP THE TAPE 4 BLOCKS IN ADVANCE OF THE TARGET BLOCK,
/IF THE BLOCK # IS LESS THAN 4:SEARCH FOR BLK 0.
	TAD DTBLK
	TAD M4
	SPA		/L=0: SEARCH BACKWARD
	 CLA
	DCA DTDTV+2
	TAD DTFUN
	AND C77
	DCA DTDTV
	TAD I DTUSTAT
	TAD (INACTIVE-EMULATE+NOBOOT /(NOBOOT IS FOR 'BO'
			/TO SHOW SOMETHING IS GOING ON
	DCA I DTUSTAT
IFZERO BGMAX-2&4000 <
	JMS TEKICK	/ >
	JMS DTDO
/NOW THE BLOCK IS NEAR-BY;CALL BG IN CORE
	TAD I DTUSTAT	/BG ACTIVE
	TAD (EMULATE-INACTIVE+INCORE/REQUEST IN CORE;LOCK IT THERE
	DCA I DTUSTAT
IFZERO BGMAX-2&4000 <
	JMS TEKICK	/ >
	TAD DTUSTAT	/NOW FIND THE SLOT-TO-WAIT-IN-CORE
	TAD (USLOT
	JMS DEFER
	DCA .+3
	JMS MONITOR	/AND WAIT FOR BG IN CORE
	   WAIT
	   0
	CLA STL		/SEARCH FORWARD
	TAD DTDTV+2
	SNA CLA		/IF BLOCK LESS THAN 4,
	 CML		/SEARCH BACKWARD
DTSHRT,	TAD DTFUN
	DCA DTDTV	/FOR THE REAL TRANSFER
	TAD DTBLK
	DCA DTDTV+2	/REA	JMP .+3
DTRET1,
IFZEREKICK	/ >
	AC4000
	DCAOR NORMAL/ERROR
	JMS MO
/DO THE SEARCH OR TRANSFER,GIVE A NUMBER OF
/RE-TRIALS;AND WAIT A LITTLE WHILE IF THE MODULE IS BUSY.
/THEN TRY AGAIN...AND AGAIN...AND AGIAN...
/DTDO RETURNS WITH AC=0 AND DF=MONFLD
DTDO,	.-.
DTTRY,	CDTOIF		/AD DTIDTV
	JMS MONITOR&3777/DT
	 JMP DTSTALL	OT	//ACCEPTED;SAVE SLOT#R COMPLETION
	   WAIT
DTSLOT,	   0
	CDF MONFLD
	SNA CLA
	  JMP I DTDO	/NO ERRORS
	JMP DTRET1	/BG ERROR ONLY

DTSTALL,JMS MONITOR	//
	   STALL
	   DGNTICK%2	/0.5 SECS
	 CLA		//
	JMP DTTRY	//

DTFUN,
IFNZRO BGMAX-1 <0	/FUNCTION WORD >
DTDTV,	0
	0
IFNZRO BGMAX-1 <0	>
DTBLK,	0

IFZERO BGMAX-2&4000 <
TEKICK,	0
	JMS MONITOR
	   SIGNAL
	   BSSLOT
	CLA CLL
	JMP I TEKICK	/ >

$$