Source Code
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These source-code files are part of a reconstructed copy of LM131 revision 1,
the final release of the Apollo 13 Lunar Module (LM) Apollo Guidance Computer
(AGC) software.
The source reconstruction began with source code of Luminary 131 previously
transcribed from a digitized copy of that program. A dump of the flight spare
core rope memory module B5, part number 2010802-171, serial number RAY 411,
was obtained. This module is the only module different between Luminary 131
and LM131 revision 1. The dump was disassembled and all changes were incorporated
into these source files. Note that page numbers in the reconstructed code match
those on the Luminary 131 printout, although the changed code would likely have
changed page numbers for a real LM131 revision 1 listing.
Comments from the original source code are prefixed with a single '#' symbol,
whereas comments added later are prefixed by "##" or "###". Report any errors
noted by creating an
issue report at the Virtual AGC
project's GitHub repository.
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015052,000002: ## Copyright: Public domain.
015053,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
015054,000004: ## Purpose: A section of LM131 revision 1.
015055,000005: ## It is part of the reconstructed source code for the final
015056,000006: ## release of the flight software for the Lunar Module's (LM)
015057,000007: ## Apollo Guidance Computer (AGC) for Apollo 13. The code has
015058,000008: ## been reconstructed from a listing of Luminary 131 and a dump
015059,000009: ## of a core rope memory module B5, part number 2010802-171,
015060,000010: ## which is the only module different between LM131 revision 1
015061,000011: ## and Luminary 131. The executable generated from this source
015062,000012: ## has been verified against the module dump, so while the names,
015063,000013: ## comments, and ordering may not be exactly correct, the
015064,000014: ## resulting binary is.
015065,000015: ## Reference: p. 366
015066,000016: ## Assembler: yaYUL
015067,000017: ## Contact: Ron Burkey <info@sandroid.org>.
015068,000018: ## Website: www.ibiblio.org/apollo/index.html
015069,000019: ## Mod history: 2022-10-28 MAS Created from Luminary 131.
015070,000020:
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Page 366
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015072,000022: 15,2050 BANK 15
015073,000023:
015074,000024: 22,2000 SETLOC KALCMON1
015075,000025: 22,2000 BANK
015076,000026:
015077,000027: # DETECTING GIMBAL LOCK
015078,000028: 22,2744 22,2744 LOCSKIRT EQUALS NOGIMLOC
015079,000029:
015080,000030: 22,2744 77614 NOGIMLOC SET
015081,000031: 22,2745 01074 CALCMAN3
015082,000032: 22,2746 70740 WCALC LXC,1 DLOAD*
015083,000033: 22,2747 01322 RATEINDX # CHOOSE THE DESIRED MANEUVER RATE
015084,000034: 22,2750 04772 ARATE,1 # FROM A LIST OF FOUR
015085,000035: 22,2751 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
015086,000036: 22,2752 44527 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
015087,000037: # ABOUT COF
015088,000038: 22,2753 74343 DLOAD* VXSC
015089,000039: 22,2754 04772 ARATE,1
015090,000040: 22,2755 03270 COF
015091,000041: 22,2756 17325 STODL BRATE # COMPONENT MANEUVER RATES 45 DEG/SEC
015092,000042: 22,2757 03335 AM
015093,000043: 22,2760 55605 DMP DDV*
015094,000044: 22,2761 05002 ANGLTIME
015095,000045: 22,2762 04772 ARATE,1
015096,000046: 22,2763 77661 SR
015097,000047: 22,2764 20606 5
015098,000048: 22,2765 03333 STORE TM # MANEUVER EXECUTION TIME SCALED AS T2
015099,000049: 22,2766 77614 SETGO
015100,000050: 22,2767 01035 CALCMAN2 # 0(OFF) = CONTINUE MANEUVER
015101,000051: 22,2770 45010 NEWANGL +1 # 1(ON) = START MANEUVER
015102,000052:
015103,000053: # THE FOUR SELECTABLE FREE FALL MANEUVER RATES SELECTED BY
015104,000054: # LOADING RATEINDX WITH 0, 2, 4, 6, RESPECTIVELY
015105,000055:
015106,000056: 22,2771 00221 24255 ARATE 2DEC .0088888888 # = 0.2 DEG/SEC $ 22.5 DEG/SEC
015107,000057: 22,2773 00554 02660 2DEC .0222222222 # = 0.5 DEG/SEC $ 22.5 DEG/SEC
015108,000058: 22,2775 02660 13301 2DEC .0888888888 # = 2.0 DEG/SEC $ 22.5 DEG/SEC
015109,000059: 22,2777 16161 30707 2DEC .4444444444 # = 10.0 DEG/SEC $ 22.5 DEG/SEC
015110,000060:
015111,000061: 22,3001 00003 04000 ANGLTIME 2DEC .0001907349 # = 100B-19 FUDGE FACTOR TO CONVERT
015112,000062: # MANEUVER ANGLE TO MANEUVER TIME
015113,000063:
015114,000064:
End of include-file GIMBAL_LOCK_AVOIDANCE.agc. Parent file is MAIN.agc