Source Code
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These source-code files are part of a reconstructed copy of Corona 261, the
final, flown release of the Block I Command Module (CM) Apollo Guidance Computer
(AGC) software for the AS-202 mission.
They have been created via disassembly of binary dumps of the original core rope
memory modules actually flown on the mission, part numbers 1003733-171, 1003733-241,
1003733-191, 1003733-211, 1003733-221, and 1003733-241. The source code for the Apollo
4 and 6 software, Solarium 55, was used as a starting point, since it was directly
derived from Corona and (at least in theory) only minimally modified.
Since only binary dumps (rather than listings) of Corona are available as source material,
all comments and labels are approximate.
They have been taken from other AGC programs where possible, or, in some places, written
from scratch to match what we believe would have been in the original listing.
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008056,000002: ## Copyright: Public domain.
008057,000003: ## Filename: IMU_COMPENSATION_PACKAGE.agc
008058,000004: ## Purpose: A section of Corona revision 261.
008059,000005: ## It is part of the source code for the Apollo Guidance Computer
008060,000006: ## (AGC) for AS-202. No original listings of this software are
008061,000007: ## available; instead, this file was created via disassembly of
008062,000008: ## the core rope modules actually flown on the mission.
008063,000009: ## Assembler: yaYUL
008064,000010: ## Contact: Ron Burkey <info@sandroid.org>.
008065,000011: ## Website: www.ibiblio.org/apollo/index.html
008066,000012: ## Mod history: 2023-05-27 MAS Created from Solarium 55.
008067,000013: ## 2023-06-17 MAS Updated for Corona.
008068,000014:
008069,000015:
008070,000016: # THE FOLLWOING ROUTINE IS DESIGNED TO COMPENSATE FOR PIPA BIAS AND SCALE FACTOR ERROR. ATTHE SAME TIME,
008071,000017: # IT ACCUMULATES GYRO TORQUE COMMANDS NECESSARY TO COMPENSATE FOR THE ASSOCIATED BIAS AND ACCELERATION-CAUSED GYRO
008072,000018: # DRIFTS. THIS ROUTINE EXPECTS TO FIND PIPA READINGS IN THE MAJOR PARTS OF DELV (DELVX, DELVY, DELVZ), WITH THE
008073,000019: # MINOR PARTS IRRELEVANT. OUTPUT FROM 1/PIPA IS DOUBLE PRECISION COMPENSATED DATA, THE MINOR PART OF WHICH USUALLY
008074,000020: # CONTAINS ALL THE COMPENSATION. 1/PIPA MUST BE CALLED AT LEAST EVERY 2.56 SECONDS, DUE TO SCALING CONSIDERATIONS.
008075,000021: # SPECIFICALLY, THE CORRECTION IS:
008076,000022:
008077,000023: # PIPA = PIPA (1 + SCALE FACTOR ERROR) - BIAS DELTAT
008078,000024: # C I
008079,000025:
008080,000026: # WHERE PIPA IS THE COMPENSATED DATA OBTAINED FROM THE SAMPLED PIPA .
008081,000027: # C I
008082,000028:
008083,000029:
008084,000030:
008085,000031: 14,7007 BANK 14
008086,000032: 14,7007 35502 1/PIPA CAF FOUR # LOOP TO PROCESS INPUT PIPA DATA.
008087,000033: 14,7010 50101 +1 TS BUF +2
008088,000034: 14,7011 20000 INDEX A
008089,000035: 14,7012 41001 CS DELVX # SAMPLED PIPA INTO MPAC
008090,000036: 14,7013 50115 TS MPAC
008091,000037: 14,7014 20101 INDEX BUF +2 # SUBTRACT BIAS TERM (LESS THAN 1 BIT).
008092,000038: 14,7015 40736 CS PIPABIAS
008093,000039: 14,7016 25777 EXTEND
008094,000040: 14,7017 40755 MP 1/PIPADT # SUPPLIED BY USER SCALED AT CS 2(-8),
008095,000041: 14,7020 50116 TS MPAC +1
008096,000042:
008097,000043: 14,7021 40115 CS MPAC # SHIFT THE PIPA READING LEFT THREE PLACES
008098,000044: 14,7022 50115 TS MPAC
008099,000045: 14,7023 25777 EXTEND # IN PREPARATION FOR SCALE FACTOR
008100,000046: 14,7024 44513 MP BIT4 # CORRECTION. IF IT OVERFLOWS, SHIFT THE
008101,000047: 14,7025 10000 CCS A # SCALE FACTOR ERROR RIGHT 11 PLACES
008102,000048: 14,7026 07205 TC PIPOVF # TAKING A LOSS IN PRECISION.
008103,000049:
008104,000050: 14,7027 07031 TC +2 # THE ABOVE HAPPENS AT DELTA VS OF OVER
008105,000051: 14,7030 07205 TC PIPOVF # 12 G-SECS., RESULTING IN A SCALE FACTOR
008106,000052: 14,7031 20101 INDEX BUF +2 # CORRECTION GOOD ONLY TO 60 PPM.
008107,000053: 14,7032 40737 CS PIPASCF
008108,000054: 14,7033 25777 EXTEND
008109,000055: 14,7034 40003 MP LP
008110,000056: 14,7035 60116 AD MPAC +1 # ADD TO BIAS CORRECTION.
008111,000057: 14,7036 20101 INDEX BUF +2
008112,000058: 14,7037 51002 TS DELVX +1 # AND MAYBE SKIP.
008113,000059: 14,7040 35501 CAF ZERO
008114,000060:
008115,000061: 14,7041 60115 AD MPAC
008116,000062: 14,7042 20101 INDEX BUF +2
008117,000063: 14,7043 51001 TS DELVX
008118,000064:
008119,000065: 14,7044 10101 PIPJUMP CCS BUF +2 # LOOP TO PROCESS NEXT COMPONENT.
008120,000066: 14,7045 64335 AD NEG1
008121,000067: 14,7046 07010 TC 1/PIPA +1
008122,000068: 14,7047 00756 LGCOMP ADRES GCOMP
008123,000069:
008124,000070:
008125,000071: # THE FOLLOWING ROUTINE COMPUTES THE GYRO TORQUES NECESSARY TO COMPENSATE FOR THE ACCELERATION-SENSITIVE
008126,000072: # DRIFTS DUE TO THE DATA JUST PROCESSED, AND SUMS THEM INTO THE GCOMP REGISTERS.
008127,000073:
008128,000074: 14,7050 50101 TS GCOMPSW # SET GYRO TORQUE INDICATOR TO ZERO.
008129,000075: 14,7051 50077 TS BUF # RELATIVE ADDRESS OF PRESENT COMPONENT.
008130,000076:
008131,000077: 14,7052 41001 CS DELVX # PROCESS X COMPONENT.
008132,000078: 14,7053 50115 TS MPAC
008133,000079: 14,7054 41002 CS DELVX +1
008134,000080: 14,7055 50116 TS MPAC +1
008135,000081: 14,7056 40747 CS ADIAX
008136,000082: 14,7057 07134 TC GCOMPSUB -1
008137,000083:
008138,000084: 14,7060 41003 CS DELVY
008139,000085: 14,7061 50115 TS MPAC
008140,000086: 14,7062 41004 CS DELVY +1
008141,000087: 14,7063 50116 TS MPAC +1
008142,000088: 14,7064 40752 CS ADSRAX
008143,000089: 14,7065 07135 TC GCOMPSUB
008144,000090:
008145,000091: 14,7066 40744 CS GBIASX # ADD IN BIAS DRIFTS.
008146,000092: 14,7067 07160 TC DRIFTSUB
008147,000093:
008148,000094: 14,7070 41003 CS DELVY # COMPUTE Y GYRO COMPENSATION.
008149,000095: 14,7071 50115 TS MPAC
008150,000096: 14,7072 41004 CS DELVY +1
008151,000097: 14,7073 50116 TS MPAC +1
008152,000098: 14,7074 40750 CS ADIAY
008153,000099: 14,7075 07134 TC GCOMPSUB -1
008154,000100:
008155,000101: 14,7076 41005 CS DELVZ
008156,000102: 14,7077 50115 TS MPAC
008157,000103: 14,7100 41006 CS DELVZ +1
008158,000104: 14,7101 50116 TS MPAC +1
008159,000105: 14,7102 40753 CS ADSRAY
008160,000106: 14,7103 07135 TC GCOMPSUB
008161,000107:
008162,000108: 14,7104 40745 CS GBIASY
008163,000109: 14,7105 07160 TC DRIFTSUB
008164,000110:
008165,000111: 14,7106 41003 CS DELVY # CORRESPONDING PATTERN FOR Z GYRO.
008166,000112: 14,7107 50115 TS MPAC
008167,000113: 14,7110 41004 CS DELVY +1
008168,000114: 14,7111 50116 TS MPAC +1
008169,000115: 14,7112 40754 CS ADSRAZ
008170,000116: 14,7113 07134 TC GCOMPSUB -1
008171,000117:
008172,000118: 14,7114 41005 CS DELVZ
008173,000119: 14,7115 50115 TS MPAC
008174,000120: 14,7116 41006 CS DELVZ +1
008175,000121: 14,7117 50116 TS MPAC +1
008176,000122: 14,7120 40751 CS ADIAZ
008177,000123: 14,7121 07134 TC GCOMPSUB -1
008178,000124:
008179,000125: 14,7122 40746 CS GBIASZ
008180,000126: 14,7123 07160 TC DRIFTSUB
008181,000127:
008182,000128: 14,7124 10101 CCS GCOMPSW # NON-ZERO IF TIME TO PUT OUT COMPENSATION
008183,000129: 14,7125 07127 TC +2
008184,000130: 14,7126 05702 TC SWRETURN # TORQUES NOT BIG ENOUGH YET.
008185,000131:
008186,000132: 14,7127 20017 INHINT
008187,000133: 14,7130 32170 CAF PRIO35 # REQUEST COMPENSATION JOB
008188,000134: 14,7131 02052 TC NOVAC
008189,000135: 14,7132 31225 CADR 1/GYRO
008190,000136:
008191,000137: 14,7133 06020 TC MODEEXIT # RELINT AND RETURN TO SWRETURN.
008192,000138:
008193,000139:
008194,000140: # SUBROUTINES USED TO ACCUMULATE GYRO COMPENSATION COMMANDS.
008195,000141:
008196,000142: 14,7134 40000 -1 COM # (ENTERS HERE TO RE-COMPLEMENT INPUT).
008197,000143: 14,7135 30116 GCOMPSUB XCH MPAC +1 # DOES DP BY SINGLE MULTIPLY WITH DP ADD
008198,000144: 14,7136 25777 EXTEND # TO STORAGE.
008199,000145: 14,7137 40116 MP MPAC +1
008200,000146: 14,7140 30116 XCH MPAC +1
008201,000147: 14,7141 25777 EXTEND
008202,000148: 14,7142 40115 MP MPAC
008203,000149: 14,7143 50034 TS OVCTR
008204,000150: 14,7144 30003 XCH LP
008205,000151: 14,7145 60116 AD MPAC +1 # (AND MAYBE INCREMENT OVCTR).
008206,000152:
008207,000153: 14,7146 20077 BIASCOMP INDEX BUF # BIAS COMPENSATION ENTERS HERE.
008208,000154: 14,7147 60757 AD GCOMP +1
008209,000155: 14,7150 20077 INDEX BUF
008210,000156: 14,7151 30757 XCH GCOMP +1
008211,000157: 14,7152 30034 XCH OVCTR
008212,000158: 14,7153 20077 INDEX BUF
008213,000159: 14,7154 60756 AD GCOMP
008214,000160: 14,7155 20077 INDEX BUF
008215,000161: 14,7156 50756 TS GCOMP
008216,000162:
008217,000163: 14,7157 00001 TC Q
008218,000164:
008219,000165:
008220,000166: # SUBROUTINE WHICH ADDS IN GYRO BIAS DRIFT, TESTS TORQUE SIZE TO SEE IF COMMANDS SHOULD BE PUT OUT, AND
008221,000167: # ADVANCES GCOMP POINTER.
008222,000168:
008223,000169: 14,7160 30001 DRIFTSUB XCH Q
008224,000170: 14,7161 50100 TS BUF +1
008225,000171: 14,7162 30001 XCH Q
008226,000172: 14,7163 25777 EXTEND
008227,000173: 14,7164 40755 MP 1/PIPADT
008228,000174: 14,7165 25777 EXTEND # RESULT WAS IN GYRO PULSES X 2(+2).
008229,000175: 14,7166 45502 MP FOUR # RE-SCALE TO ADD INTO GCOMP REGISTER.
008230,000176: 14,7167 50034 TS OVCTR
008231,000177: 14,7170 30003 XCH LP # GO TO STANDARD INCREMENT ROUTINE.
008232,000178: 14,7171 07146 DRFTSUB2 TC BIASCOMP
008233,000179:
008234,000180: 14,7172 35503 CAF TWO # INCREMENT POINTER AND
008235,000181: 14,7173 60077 AD BUF
008236,000182: 14,7174 30077 XCH BUF # CHECK MAGNITUDE OF TORQUE COMMAND. IF
008237,000183: 14,7175 20000 INDEX A # SUFFICIENTLY LARGE, SET GCOMPSW PNZ TO
008238,000184: 14,7176 10756 CCS GCOMP # CALL FOR COMPENSATION JOB, 1/GYRO.
008239,000185: 14,7177 07201 TC +2 # GETS DABS OF COMMAND.
008240,000186: 14,7200 00100 TC BUF +1
008241,000187:
008242,000188: 14,7201 77246 MASK COMPCHK
008243,000189: 14,7202 10000 CCS A
008244,000190: 14,7203 50101 TS GCOMPSW
008245,000191: 14,7204 00100 TC BUF +1 # RETURN.
008246,000192:
008247,000193:
008248,000194: # (1/PIPA COMES HERE IF PIPA COUNTER SHOWED A DELTA V OF OVER 12 G-SEC.)
008249,000195:
008250,000196: 14,7205 20101 PIPOVF INDEX BUF +2 # SHIFT THE SCALE FACTOR RIGHT 11 ON OVF.
008251,000197: 14,7206 40737 CS PIPASCF
008252,000198: 14,7207 25777 EXTEND
008253,000199: 14,7210 44513 MP BIT4
008254,000200: 14,7211 25777 EXTEND # FORM DP INCREMENT TO DELV IN THIS CASE.
008255,000201: 14,7212 40115 MP MPAC
008256,000202: 14,7213 50034 TS OVCTR
008257,000203:
008258,000204: 14,7214 30003 XCH LP
008259,000205: 14,7215 60116 AD MPAC +1 # MAYBE INCREMENTING OVCTR.
008260,000206: 14,7216 20101 INDEX BUF +2
008261,000207: 14,7217 31002 XCH DELVX +1 # NO SKIP SINCE OVCTR SET.
008262,000208: 14,7220 30034 XCH OVCTR
008263,000209: 14,7221 60115 AD MPAC
008264,000210: 14,7222 20101 INDEX BUF +2
008265,000211: 14,7223 31001 XCH DELVX
008266,000212: 14,7224 07044 TC PIPJUMP # JUMP ON LOOP COUNTER.
008267,000213:
008268,000214:
008269,000215: # THE FOLLOWING JOB IS INITIATED BY 1/PIPA TO PUT OUT COMPENSATING GYRO TORQUE COMMANDS.
008270,000216:
008271,000217: 14,7225 34504 1/GYRO CAF BIT11 # IF MODE SWITCH IN PROGRESS, DONT PUT
008272,000218: 14,7226 70646 MASK FLAGWRD1 # OUT COMPENSATION THIS TIME.
008273,000219: 14,7227 10000 CCS A
008274,000220: 14,7230 02124 TC ENDOFJOB
008275,000221:
008276,000222: 14,7231 03424 TC FLAG1UP # SHOW IMU ACTIVITY
008277,000223: 14,7232 02000 OCT 02000 # FLAG TURNED OFF BY GYRO ROUTINES.
008278,000224:
008279,000225: 14,7233 37047 CAF LGCOMP # DISABLE THE T4RUPT CDU DRIVE THEMSELVES.
008280,000226: 14,7234 05654 TC BANKCALL
008281,000227: 14,7235 31335 CADR GYROSPNT # NO TWITCH (2+2-) ON ZERO INPUT.
008282,000228:
008283,000229: 14,7236 05654 TC BANKCALL
008284,000230: 14,7237 30331 CADR IMUSTALL
008285,000231: 14,7240 03074 TC CURTAINS
008286,000232:
008287,000233: 14,7241 35501 CAF ZERO # ZERO GCOMP REGSITERS SINCE COMMANDS HAVE
008288,000234: 14,7242 50756 TS GCOMP # BEEN PUT OUT.
008289,000235: 14,7243 50760 TS GCOMP +2
008290,000236: 14,7244 50762 TS GCOMP +4
008291,000237:
008292,000238: 14,7245 02124 TC ENDOFJOB
008293,000239:
008294,000240: 14,7246 77740 COMPCHK OCT -37 # COMMANDS MUST BE AT LEAST 32 PLS.
008295,000241:
008296,000242:
008297,000243: # THE FOLLOWING ROUTINE SUPPLIES GYRO DRIFT COMPENSATION DURING THOSE PORTIONS OF A MISSION WHICH DO NOT
008298,000244: # USE PIPA DATA. THIS JOB IS CALLED EVERY 81.93 SECONDS (WHEN APPROPRIATE) BY THE IDLE TASK.
008299,000245:
008300,000246: 14,7247 40036 BIASONLY CS TIME1 # COMPUTE TIME DIFFERENCE (ALMOST ALWAYS
008301,000247: 14,7250 40000 COM # 81.93 SECS.).
008302,000248: 14,7251 30755 XCH OLDBT1
008303,000249: 14,7252 40000 COM
008304,000250: 14,7253 60755 AD OLDBT1
008305,000251: 14,7254 10000 BONLY2 CCS A # LASTBIAS ENTERS HERE.
008306,000252: 14,7255 64516 AD ONE
008307,000253: 14,7256 07263 TC BONLY3
008308,000254: 14,7257 07261 TC +2
008309,000255: 14,7260 02124 TC ENDOFJOB # MAY HAVE A COMPUTED DIFF = 0.
008310,000256:
008311,000257: 14,7261 40000 COM
008312,000258: 14,7262 64476 AD POSMAX
008313,000259:
008314,000260: 14,7263 25777 BONLY3 EXTEND # FORM DELTA-T AT 2(+8) CS.
008315,000261: 14,7264 44506 MP BIT9 # SHIFT RIGHT 6.
008316,000262: 14,7265 50115 TS MPAC
008317,000263: 14,7266 50106 TS TEM9
008318,000264: 14,7267 30003 XCH LP
008319,000265: 14,7270 50116 TS MPAC +1
008320,000266: 14,7271 50107 TS TEM10
008321,000267: 14,7272 35501 CAF ZERO
008322,000268: 14,7273 50101 TS GCOMPSW
008323,000269: 14,7274 50077 TS BUF
008324,000270:
008325,000271: 14,7275 40744 CS GBIASX # DO X, Y, AND THEN Z.
008326,000272: 14,7276 07317 TC FBIASSUB
008327,000273:
008328,000274: 14,7277 40106 CS TEM9 # RELOAD DT.
008329,000275: 14,7300 50115 TS MPAC
008330,000276: 14,7301 40107 CS TEM10
008331,000277: 14,7302 50116 TS MPAC +1
008332,000278: 14,7303 40745 CS GBIASY
008333,000279: 14,7304 07316 TC FBIASSUB -1
008334,000280:
008335,000281: 14,7305 40106 CS TEM9
008336,000282: 14,7306 50115 TS MPAC
008337,000283: 14,7307 40107 CS TEM10
008338,000284: 14,7310 50116 TS MPAC +1
008339,000285: 14,7311 40746 CS GBIASZ
008340,000286: 14,7312 07316 TC FBIASSUB -1
008341,000287: 14,7313 10101 CCS GCOMPSW # PUT OUT COMPENSATION IF CALLED FOR.
008342,000288: 14,7314 07225 TC 1/GYRO
008343,000289: 14,7315 02124 TC ENDOFJOB
008344,000290:
008345,000291: 14,7316 40000 -1 COM
008346,000292: 14,7317 30001 FBIASSUB XCH Q
008347,000293: 14,7320 50100 TS BUF +1
008348,000294: 14,7321 35501 CAF ZERO
008349,000295: 14,7322 50117 TS MPAC +2
008350,000296: 14,7323 30001 XCH Q
008351,000297: 14,7324 05416 TC SHORTMP
008352,000298: 14,7325 30115 XCH MPAC
008353,000299: 14,7326 50034 TS OVCTR
008354,000300: 14,7327 30116 XCH MPAC +1
008355,000301: 14,7330 07171 TC DRFTSUB2 # RETURN TO CALLER VIA BUF +1.
008356,000302:
008357,000303: 14,7331 30755 LASTBIAS XCH OLDBT1 # COMES HERE FOR TRANSITION TO PIPA READ-
008358,000304: 14,7332 40000 COM # ING MODE. NEW VALUE OF 1/PIPADT ARRIVES
008359,000305: 14,7333 60115 AD MPAC # IN A WITH WITH TIME1 AT PIPA ZEROING IN
008360,000306: 14,7334 07254 TC BONLY2 # MPAC. EXITS VIA ENDOFJOB.
End of include-file IMU_COMPENSATION_PACKAGE.agc. Parent file is MAIN.agc