/	MDC8 IOT DEFINITIONS.

	IFNDEF	DEVCODE	<DEVCODE=70>	/USES 670X BY DEFAULT

	DSEI=	DEVCODE^10+6000		/INTERRUPT ENABLE/DISABLE PER AC[11]
	DSSF=	DEVCODE^10+6001		/SKIP ON DONE FLAG
	DSCF=	DEVCODE^10+6002		/CLEAR DONE FLAG
	DSHI=	DEVCODE^10+6003		/LOAD HIGH-ORDER COMMAND ADDRESS
	DSGO=	DEVCODE^10+6004		/LOAD LOW-ORDER COMMAND AND GO
/	    =	DEVCODE^10+6005		/UNUSED
	DSRS=	DEVCODE^10+6006		/READ STATUS
	DSIM=	DEVCODE^10+6007		/INTERFACE MAINTENANCE INSTRUCTION

/ Commands live in memory and are retrieved with DMA.  Here's the memory layout for
/ the command.
TABLE,	6!DMA			/TABLE LENGTH PLUS DMA INDICATOR
RWCOM,	.-.&377			/0010 IF READING, 0012 IF WRITING
				/0000 TEST READY
				/0006 FORMAT TRACK
				/0010 READ DATA
				/0012 WRITE DATA
				/0013 SEEK
				/0015 SEEK STATUS
				/0300 DEFINE DISK FORMAT
				/0354 READ DMA BUFFER
				/0357 WRITE DMA BUFFER
SECTHI,	.-.&377			/UNIT BITS AND HIGH-ORDER SECTOR ADDRESS
				/(UNIT^40 + SECTH)
SECTMD,	.-.&377			/MIDDLE SECTOR ADDRESS
SECTLO,	.-.&377			/LOW-ORDER SECTOR ADDRESS
SCTCNT,	.-.&377			/SECTOR COUNTER (1-40)
CONTRL,	0&377			/CONTROL WORD
				/???
TRFLD,	.-.&377			/BANK (0000) AND TRANSFER FIELD (0-7)
				/(FIELD IN 9-11)
				/MORE BITS TO INCLUDE A BANK, UP TO 128K
TRADDR,	.-.			/TRANSFER ADDRESS
/ N.B. Most of these are *byte* values, not word values, as indicate by
/ the masking with 0377.
/
/ Note also that the addressing is by logical sector number, so an OS/8
/ driver must scale block numbers by 2 (sectors per block)..

/ The DSRS IOT can be used to retrieve status.  The top bit is BUSY; any other
/ bit signifies an error occurred.  The exact meaning of individual bits is
/ not yet known.

/ To initiate a read/write, the above block is initialized, then typically a
/ RIF IOT is done to get the current IF, which is loaded into the controller
/ by the DSHI IOT.  Then the address of TABLE is loaded into the controller
/ with a DSGO IOT.

/ Between attempts to talk to the controller, the status should be polled
/ with DSRS until it shows not BUSY, and then cleared with DSCF.  This
/ includes the interval between DSHI and DSGO, above.

/ Once a command is initiated, one again uses DSSF to wait for controller ready
/ then DSCF / to clear the done flag.  Then a DSIM IOT can be issued to wait
/ for the actual I/O (as opposed to waiting for the controller).  When the
/ DSIM reports complete, the I/O is done.

/ Command values for DSIM are not yet known, but allow formatting and other
/ maintenance operations.

/ Some of the programs seem to use a sequence of a half-dozen "AND I 0"
/ instructions as a delay, rather than fiddle about with the status register.