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These were all files included in MIT's 1999 release of SYSDOC and SYSTEM, so they need the license header. CHAORD is an XGP text file; XGP processors should ignore unknown directives so ;comment should work.
112 lines
3.6 KiB
Plaintext
Executable File
112 lines
3.6 KiB
Plaintext
Executable File
Copyright (c) 1999 Massachusetts Institute of Technology
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See the COPYING file at the top-level directory of this project.
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------------------------------
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SUBTTL I/O DEVICE DISPATCH TABLES
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COMMENT |
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This page tries to document the ITS I/O device dispatch tables and
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dispatch environment. It is not completed yet.
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The tables use several different indices, which are:
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opnidx - result of device name lookup in DEVTAB
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ioidx - result of OPEN; has symbolic values. This is the index
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stored in RH of IOCHNM (per-job channel table)
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sidx - secondary index from DCHSTB(ioidx)
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ridx - secondary index from RSTB(ioidx)
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The following system calls are dispatched through these tables.
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There are 11 dispatch routines that each device must specify.
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The format is "CALL [table name(index-used) -> device-routine]"
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Unless otherwise noted, context for all routines has
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U/ User index
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R/ addr of IOCHNM word for specified channel
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and the phrase "all ACs can be used" excludes P and U, of course.
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and routines can hang (u.o.n.)
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OPEN [DEVADR(opnidx) -> devO]
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"opnidx" is looked up from DEVTAB which holds the device names.
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The device's OPEN routine is in the RH of DEVADR.
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It must set up the user's IOCHNM word for the channel,
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by setting the RH to the right "ioidx" and the LH to whatever
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the device wants.
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Context:
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A/ FN1
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B/ FN2
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C/ <mode bits>,,<device name>
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D/ <mode bits rotated -1>
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E/ <device name>
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TT/ DEVADR word <bits>,,<routine>
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W/ "open" command (0= Normal R/W open, 1= Write-over mode,
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2= Make link, 4= Delete or rename)
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SRN3(U),SRN4(U),SRN5(U) - args 4,5,6 (if present)
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Routine is JRST'd to, and must return via POPJ1 for success.
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Errors should JRST to the appropriate OPNLnn label.
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All ACs can be smashed.
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CLOSE [CLSTB(ioidx) -> devCLS]
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The device's CLOSE routine is in the RH of CLSTB.
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Context:
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A/ 0,,<LH of IOCHNM word>
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B/ 0,,<RH of IOCHNM word>
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C/ CLSTB entry, <bits>,,<rtn addr>
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R/ addr of IOCHNM word
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Called via PUSHJ, must return via POPJ (IOCHNM and IOCHST will
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be cleared immediately after return).
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Can smash all ACs including R.
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Must NOT hang!
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IOT, SIOT [IOTTB(ioidx) -> devVarious]
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These routines do I/O transfers. The main reason "ioidx"
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has so many possible values (causing IOTTB to be large) is
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because lots of devices specify different ioidx's for different
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modes - input/output, block/unit, image/ascii, etc - in order
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to speed up actual I/O transfers, which are probably the most
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common device-related system calls.
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Context:
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Boy is this complicated.
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STATUS [LH(DSTSTB(sidx)) -> devSTA]
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Context:
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R/ addr of IOCHNM word
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Called by PUSHJ, must return by POPJ
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Must return in RH(D) some device-dependent status stuff.
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Calling routine (NSTATUS) fills in the LH from IOCHST.
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Must not smash C,R! Probably should not smash other
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stuff either, depending on what USRVAR/USET need.
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WHYINT [RH(DSTSTB(sidx)) -> devWHY]
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RCHST, RFNAME [LH(DRFNTB(sidx)) -> devRCH]
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RFPNTR [RH(DRFNTB(sidx)) -> devRFP]
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IOPUSH, IOPOP [LH(RSTB1(ridx)) -> devIOP]
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RESET [RH(RSTB1(ridx)) -> devRST]
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Context:
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R/ addr of IOCHNM wd
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Called by JRST from NRESET/ARESET/AIOPP1, must return by POPJ.
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Can clobber all ACs. Must not hang.
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FORCE [LH(DFRCTB(ridx)) -> devFRC]
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Context:
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A/ LH of IOCHNM word, in RH.
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H/ IOCHNM word
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R/ <LH of CLSTB entry>,,<addr of IOCHNM word>
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Called by JRST from NFORCE. Returns by POPJ1 for win,
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POPJ if fail. Should not clobber context that FINISH routine
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may need.
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FINISH [RH(DFRCTB(ridx)) -> devFIN]
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Same as FORCE, except that FORCE is called first, thus
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context is whatever FORCE leaves behind. This routine
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must do the actual waiting for FORCE's actions to be
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finished.
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