RCS_FAILURE_MONITOR.agc
### FILE="Main.annotation"
## Copyright: Public domain.
## Filename: RCS_FAILURE_MONITOR.agc
## Purpose: A section of Luminary revision 173.
## It is part of the reconstructed source code for the second
## (unflown) release of the flight software for the Lunar
## Module's (LM) Apollo Guidance Computer (AGC) for Apollo 14.
## The code has been recreated from a reconstructed copy of
## Luminary 178, as well as Luminary memo 167 (revision 1).
## It has been adapted such that the resulting bugger words
## exactly match those specified for Luminary 173 in NASA
## drawing 2021152N, which gives relatively high confidence
## that the reconstruction is correct.
## Reference: pp. 196-198
## Assembler: yaYUL
## Contact: Ron Burkey <info@sandroid.org>.
## Website: www.ibiblio.org/apollo/index.html
## Mod history: 2019-09-18 MAS Created from Luminary 178.
## Page 196
# PROGRAM DESCRIPTION
# AUTHOR: J S MILLER
# MODIFIED 6 MARCH 1968 BY P S WEISSMAN TO SET UP JOB FOR 1/ACCS WHEN THE MASKS ARE CHANGED.
# THIS ROUTINE IS ATTACHED TO T4RUPT, AND IS ENTERED EVERY 480 MS. ITS FUNCTION IS TO EXAMINE THE LOW 8 BITS
# OF CHANNEL 32 TO SEE IF ANY ISOLATION-VALVE CLOSURE BITS HAVE APPEARED OR DISAPPEARED (THE CREW IS WARNED OF JET
# FAILURES BY LAMPS LIT BY THE GRUMMAN FAILURE-DETECTION CIRCUITRY; THEY MAY RESPOND BY OPERATING SWITCHES WHICH
# ISOLATE PAIRS OF JETS FROM THE PROPELLANT TANKS AND SET BITS IN CHANNEL 32). IN THE EVENT THAT CHANNEL 32 BITS
# DIFFER FROM 'PVALVEST', THE RECORD OF ACTIONS TAKEN BY THIS ROUTINE, THE APPROPRIATE BITS IN 'CH5MASK' &
# 'CH6MASK', USED BY THE DAP JET-SELECTION LOGIC, ARE UPDATED, AS IS 'PVALVEST'. TO SPEED UP & SHORTEN THE
# ROUTINE, NO MORE THAN ONE CHANGE IS ACCEPTED PER ENTRY. THE HIGHEST-NUMBERED BIT IN CHANNEL 32 WHICH REQUIRES
# ACTION IS THE ONE PROCESSED.
# THE CODING IN THE FAILURE MONITOR HAS BEEN WRITTEN SO AS TO HAVE ALMOST COMPLETE RESTART PROTECTION. FOR
# EXAMPLE, NO ASSUMPTION IS MADE WHEN SETTING A 'CH5MASK' BIT TO 1 THAT THE PREVIOUS STATE IS 0, ALTHOUGH IT OF
# COURSE SHOULD BE. ONE CASE WHICH MAY BE SEEN TO EVADE PROTECTION IS THE OCCURRENCE OF A RESTART AFTER UPDATING
# ONE OR BOTH DAP MASK-WORDS BUT BEFORE UPDATING 'PVALVEST', COUPLED WITH A CHANGE IN THE VALVE-BIT BACK TO ITS
# FORMER STATE. THE CONSEQUENCE OF THIS IS THAT THE NEXT ENTRY WOULD NOT SEE THE CHANGE INCOMPLETELY INCORP-
# ORATED BY THE LAST PASS (BECAUSE IT WENT AWAY AT JUST THE RIGHT TIME), BUT THE DAP MASK-WORDS WILL BE INCORRECT.
# THIS COMBINATION OF EVENTS SEEMS QUITE REMOTE, BUT NOT IMPOSSIBLE UNLESS THE CREW OPERATES THE SWITCHES AT HALF-
# SECOND INTERVALS OR LONGER. IN ANY EVENT, A DISAGREEMENT BETWEEN REALITY AND THE DAP MASKS WILL BE CURED IF
# THE MISINTERPRETED SWITCH IS REVERSED AND THEN RESTORED TO ITS CORRECT POSITION (SLOWLY).
# CALLING SEQUENCE:
# TCF RCSMONIT (IN INTERRUPT MODE, EVERY 480 MS.)
# EXIT: TCF RCSMONEX (ALL PATHS EXIT VIA SUCH AN INSTRUCTION)
RCSMONEX EQUALS RESUME
# ERASABLE INITIALIZATION REQUIRED:
# VIA FRESH START: PVALVEST = +0 (ALL JETS ENABLED)
# CH5MASK, CH6MASK = +0 (ALL JETS OK)
# OUTPUT: CH5MASK & CH6MASK UPDATED (1'S WHERE JETS NOT TO BE USED, IN CHANNEL 5 & 6 FORMAT)
# PVALTEST UPDATED (1,S WHEN VALVE CLOSURES HAVE BEEN TRANSLATED INTO CH5MASK & CH6MASK; CHAN 32 FORMAT)
# JOB TO DO 1/ACCS.
# DEBRIS: A, L, Q AND DEBRIS OF NOVAC.
# SUBROUTINE CALLED: NOVAC.
EBANK= CH5MASK
BANK 23
SETLOC RCSMONT
BANK
## Page 197
COUNT* $$/T4RCS
RCSMONIT EQUALS RCSMON
RCSMON CS ZERO
EXTEND
RXOR CHAN32 # PICK UP + INVERT INVERTED CHANNEL 32.
MASK LOW8 # KEEP JET-FAIL BITS ONLY.
TS Q
CS PVALVEST # - -
MASK Q # FORM PC + PC.
TS L # (P = PREVIOUS ISOLATION VALVE STATE,
CS Q # C = CURRENT VALVE STATE (CH 32)).
MASK PVALVEST
ADS L # RESULT NZ INDICATES ACTION REQUIRED.
EXTEND
BZF RCSMONEX # QUIT IF NO ACTION REQUIRED.
EXTEND
MP BIT7 # MOVE BITS 8 - 1 OF A TO 14 - 7 OF L.
XCH L # ZERO TO L IN THE PROCESS.
-3 INCR L
DOUBLE # BOUND TO GET OVERFLOW IN THIS LOOP,
OVSK # SINCE WE ASSURED INITIAL NZ IN A.
TCF -3
INDEX L
CA BIT8 -1 # SAVE THE RELEVANT BIT (8 - 1).
TS Q
MASK PVALVEST # LOOK AT PREVIOUS VALVE STATE BIT.
CCS A
TCF VOPENED # THE VALVE HAS JUST BEEN OPENED.
CS CH5MASK # THE VALVE HAS JUST BEEN CLOSED.
INDEX L
MASK 5FAILTAB
ADS CH5MASK # SET INHIBIT BIT FOR CHANNEL 5 JET.
CS CH6MASK
INDEX L
MASK 6FAILTAB
ADS CH6MASK # SET INGIBIT BIT FOR CHANNEL 6 JET.
CA Q
ADS PVALVEST # RECORD ACTION TAKEN.
TCF 1/ACCFIX # SET UP 1/ACCJOB AND EXIT.
## Page 198
VOPENED INDEX L # A VALVE HAS JUST BEEN OPENED.
CS 5FAILTAB
MASK CH5MASK
TS CH5MASK # REMOVE INHIBIT BIT FOR CHANNEL 5 JET.
INDEX L
CS 6FAILTAB
MASK CH6MASK
TS CH6MASK # REMOVE INHIBIT BIT FOR CHANNEL 6 JET.
CS Q
MASK PVALVEST
TS PVALVEST # RECORD ACTION TAKEN.
1/ACCFIX CAF PRIO27 # SET UP 1/ACCS SO THAT THE SWITCH CURVES
TC NOVAC # FOR TJETLAW CAN BE MODIFIED IF CH5MASK
EBANK= AOSQ # HAS BEEN ALTERED.
2CADR 1/ACCJOB
TCF RCSMONEX # EXIT.
5FAILTAB EQUALS -1 # CH 5 JET BIT CORRESPONDING TO CH 32 BIT:
OCT 00040 # 8
OCT 00020 # 7
OCT 00100 # 6
OCT 00200 # 5
OCT 00010 # 4
OCT 00001 # 3
OCT 00004 # 2
OCT 00002 # 1
6FAILTAB EQUALS -1 # CH 6 JET BIT CORRESPONDING TO CH 32 BIT:
OCT 00010 # 8
OCT 00020 # 7
OCT 00004 # 6
OCT 00200 # 5
OCT 00001 # 4
OCT 00002 # 3
OCT 00040 # 2
OCT 00100 # 1