Source Code

These source-code files derive from a printout of Luminary 116 (the Apollo 12 Lunar Module guidance computer program), from the personal library of original AGC developer Don Eyles, digitally photographed at archive.org, financially sponsored by Ron Burkey, and transcribed to source code by a team of volunteers. This colorized, syntax-highlighted form was created by assembling that transcribed source code. Note that the full page images are available on the Virtual AGC project page at archive.org, while reduced-size images are presented at the VirtualAGC project website. Report or fix any transcription errors at the Virtual AGC project code repository.

Notations on the program listing read, in part:

	GAP:  ASSEMBLE REVISION 116 OF AGC PROGRAM LUMINARY BY NASA 2021112-071
	19:09 AUG. 11,1969
Note that the date is the date of the printout, not the date of the program revision.

033591,000002:                                                                                                  ## Copyright:   Public domain.
033592,000003:                                                                                                  ## Filename:    THROTTLE_CONTROL_ROUTINES.agc
033593,000004:                                                                                                  ## Purpose:     A section of Luminary revision 116.
033594,000005:                                                                                                  ##              It is part of the source code for the Lunar Module's (LM)
033595,000006:                                                                                                  ##              Apollo Guidance Computer (AGC) for Apollo 12.
033596,000007:                                                                                                  ##              This file is intended to be a faithful transcription, except
033597,000008:                                                                                                  ##              that the code format has been changed to conform to the
033598,000009:                                                                                                  ##              requirements of the yaYUL assembler rather than the
033599,000010:                                                                                                  ##              original YUL assembler.
033600,000011:                                                                                                  ## Reference:   pp. 786-790
033601,000012:                                                                                                  ## Assembler:   yaYUL
033602,000013:                                                                                                  ## Contact:     Ron Burkey <info@sandroid.org>.
033603,000014:                                                                                                  ## Website:     www.ibiblio.org/apollo/index.html
033604,000015:                                                                                                  ## Mod history: 2017-01-22 MAS  Created from Luminary 99.
033605,000016:                                                                                                  ##              2017-03-01 HG   Transcribed
033606,000017:                                                                                                  ##              2017-03-14 RSB  Proofed comment text via 3-way diff vs
033607,000018:                                                                                                  ##                              Luminary 99 and 131. No problems were found,
033608,000019:                                                                                                  ##                              but a ##-comment that wouldn't have been 
033609,000020:                                                                                                  ##                              displayed properly was fixed.
033610,000021:                                                                                                  ##              2017-03-16 RSB  Comment-text fixes identified in 5-way
033611,000022:                                                                                                  ##                              side-by-side diff of Luminary 69/99/116/131/210.
033612,000023: 

Page 786

033614,000025: 31,2144                                           BANK     31                                    
033615,000026: 
033616,000027: 31,2000                                           SETLOC   FTHROT                                
033617,000028: 
033618,000029: 31,2000                                           BANK                                           
033619,000030: 
033620,000031: 31,2144  E7,1612                                  EBANK=   PIF                                   
033621,000032: 
033622,000033: 31,2144                                           COUNT*   $$/THROT                              
033623,000034:                                                                                                  #  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
033624,000035: 
033625,000036:                                                                                                  #      HERE FC, DESIRED THRUST, AND FP, PRESENT THRUST, UNWEIGHTED, ARE COMPUTED.
033626,000037: 
033627,000038: 
033628,000039: 31,2144           31245        THROTTLE           CA       ABDELV                                #  COMPUTE PRESENT ACCELERATION IN UNITS OF
033629,000040: 31,2145           00006                           EXTEND                                         #    2(-4) M/CS/CS, SAVING SERVICER TROUBLE
033630,000041: 31,2146           72345                           MP       /AF/CNST                              
033631,000042: 31,2147           00006                 +3        EXTEND                                         
033632,000043: 31,2150           23607                           QXCH     RTNHOLD                               
033633,000044: 31,2151           02326        AFDUMP             TC       MASSMULT                              
033634,000045: 31,2152           53470                           DXCH     FP                                    #  FP = PRESENT THRUST
033635,000046: 31,2153           00006                           EXTEND                                         
033636,000047: 31,2154           31464                           DCA      /AFC/                                 
033637,000048: 31,2155           02326                           TC       MASSMULT                              
033638,000049: 31,2156           55615                           TS       FC                                    #  FC = THRUST DESIRED BY GUIDANCE
033639,000050: 31,2157           53466                           DXCH     FCODD                                 #  FCODD = WHAT IT IS GOING TO GET
033640,000051: 
033641,000052: 
033642,000053:                                                                                                  #      IF IT HAS BEEN LESS THAN 3 SECONDS SINCE THE LAST THROTTLING, AUGMENT FP USING THE FWEIGHT CALCULATED THEN.
033643,000054: 
033644,000055: 
033645,000056: 31,2160           41617                           CS       TTHROT                                #  THIS CODING ASSUMES A FLATOUT WITHIN
033646,000057: 31,2161           60025                           AD       TIME1                                 #    80 SECONDS BEFORE FIRST THROTTLE CALL
033647,000058: 31,2162           74733                           MASK     POSMAX                                
033648,000059: 31,2163           40000                           COM                                            
033649,000060: 31,2164           65002                           AD       3SECS                                 
033650,000061: 31,2165           00006                           EXTEND                                         
033651,000062: 31,2166           62172                           BZMF     WHERETO                               #  BRANCH IF (TIME1-TTHROT +1) > 3 SECONDS
033652,000063: 31,2167           00006                           EXTEND                                         
033653,000064: 31,2170           31611                           DCA      FWEIGHT                               
033654,000065: 31,2171           21470                           DAS      FP                                    
033655,000066: 
033656,000067: 
033657,000068:                                                                                                  #      THIS LOGIC DETERMINES THE THROTTLING IN THE REGION 10% - 94%.   THE MANUAL THROTTLE, NOMINALLY SET AT
033658,000069:                                                                                                  #  MINIMUM BY ASTRONAUT OR MISSION CONTROL PROGRAMS, PROVIDES THE LOWER BOUND.   A STOP IN THE THROTTLE HARDWARE
033659,000070:                                                                                                  #  PROVIDES THE UPPER.
033660,000071: 
033661,000072: 
033662,000073: 31,2172           35014        WHERETO            CA       EBANK5                                #  INITIALIZE L*WCR*T AND H*GHCR*T FROM
033663,000074: 31,2173           54003                           TS       EBANK                                 #    PAD LOADED ERASABLES IN W-MATRIX
033664,000075: 

Page 787

033666,000077: 31,2174  E5,1506                                  EBANK=   LOWCRIT                               
033667,000078: 31,2174           00006                           EXTEND                                         
033668,000079: 31,2175           31507                           DCA      LOWCRIT                               
033669,000080: 31,2176           52131                           DXCH     L*WCR*T                               
033670,000081: 31,2177           35016                           CA       EBANK7                                
033671,000082: 31,2200           54003                           TS       EBANK                                 
033672,000083: 31,2201  E7,1612                                  EBANK=   PIF                                   
033673,000084: 31,2201           44755                           CS       ZERO                                  #  INITIALIZE PIFPSET
033674,000085: 31,2202           55606                           TS       PIFPSET                               
033675,000086: 31,2203           40131                           CS       H*GHCR*T                              
033676,000087: 31,2204           61620                           AD       FCOLD                                 
033677,000088: 31,2205           00006                           EXTEND                                         
033678,000089: 31,2206           62220                           BZMF     LOWFCOLD                              #  BRANCH IF FCOLD < OR = HIGHCRIT
033679,000090: 31,2207           40130                           CS       L*WCR*T                               
033680,000091: 31,2210           61465                           AD       FCODD                                 
033681,000092: 31,2211           00006                           EXTEND                                         
033682,000093: 31,2212           62215                           BZMF     FCOMPSET                              #  BRANCH IF FC < OR = LOWCRIT
033683,000094: 31,2213           31467                           CA       FP                                    #  SEE NOTE 1
033684,000095: 31,2214           12225                           TCF      FLATOUT1                              
033685,000096: 
033686,000097: 31,2215           42002        FCOMPSET           CS       FMAXODD                               #  SEE NOTE 2
033687,000098: 31,2216           61467                           AD       FP                                    
033688,000099: 31,2217           12227                           TCF      FLATOUT2                              
033689,000100: 
033690,000101: 31,2220           40131        LOWFCOLD           CS       H*GHCR*T                              
033691,000102: 31,2221           61465                           AD       FCODD                                 
033692,000103: 31,2222           00006                           EXTEND                                         
033693,000104: 31,2223           62230                           BZMF     DOPIF                                 #  BRANCH IF FC < OR = HIGHCRIT
033694,000105: 
033695,000106: 31,2224           32003                           CA       FMAXPOS                               #  NO:   THROTTLE-UP
033696,000107: 31,2225           53466        FLATOUT1           DXCH     FCODD                                 
033697,000108: 31,2226           34737                           CA       FEXTRA                                
033698,000109: 31,2227           55606        FLATOUT2           TS       PIFPSET                               
033699,000110: 
033700,000111:                                                                                                  #  NOTE 1   FC IS SET EQUAL TO FP SO PIF WILL BE ZERO.   THIS IS DESIRABLE
033701,000112:                                                                                                  #           AS THERE IS ACTUALLY NO THROTTLE CHANGE.
033702,000113: 
033703,000114:                                                                                                  #  NOTE2    HERE, SINCE WE ARE ABOUT TO RETURN TO THE THROTTLEABLE REGION
033704,000115:                                                                                                  #           (BELOW 55%) THE QUANTITY -(FMAXODD - FP) IS COMPUTED AND PUT
033705,000116:                                                                                                  #           INTO PIFPSET TO COMPENSATE FOR THE DIFFERENCE BETWEEN THE
033706,000117:                                                                                                  #           NUMBER OF BITS CORRESPONDING TO FULL THROTTLE (FMAXODD) AND THE
033707,000118:                                                                                                  #           NUMBER CORRESPONDING TO ACTUAL THRUST (FP).   THUS THE TOTAL
033708,000119:                                                                                                  #           THROTTLE COMMAND PIF = FC - FP - (FMAXODD - FP) = FC - FMAXODD.
033709,000120: 
033710,000121: 31,2230           03717        DOPIF              TC       FASTCHNG                              
033711,000122: 31,2231           00006                           EXTEND                                         
033712,000123: 31,2232           31466                           DCA      FCODD                                 
033713,000124: 31,2233           55620                           TS       FCOLD                                 
033714,000125: 31,2234           53613                           DXCH     PIF                                   
033715,000126: 31,2235           00006                           EXTEND                                         
033716,000127: 

Page 788

033718,000129: 31,2236           41470                           DCS      FP                                    
033719,000130: 31,2237           21613                           DAS      PIF                                   #  PIF = FC - FP, NEVER EQUALS +0
033720,000131: 
033721,000132: 
033722,000133: 31,2240           31612        DOIT               CA       PIF                                   
033723,000134: 31,2241           61606                           AD       PIFPSET                               #  ADD IN PIFPSET, WITHOUT CHANGING PIF
033724,000135: 31,2242           55614                           TS       PSEUDO55                              

Note: The above statement has a blue check mark right after the operand

033726,000137: 31,2243           54055                           TS       THRUST                                
033727,000138: 31,2244           34750                           CAF      BIT4                                  
033728,000139: 31,2245           00006                           EXTEND                                         
033729,000140: 31,2246           05014                           WOR      CHAN14                                
033730,000141: 31,2247           30025                           CA       TIME1                                 
033731,000142: 31,2250           55617                           TS       TTHROT                                

Note: Three statements above are marked with a single light vertical pen mark to the right of the operands

033733,000144: 
033734,000145:                                                                                                  #      SINCE /AF/ IS NOT AN INSTANTANEOUS ACCELERATION, BUT RATHER AN "AVERAGE" OF THE ACCELERATION LEVELS DURING
033735,000146:                                                                                                  #  THE PRECEEDING PIPA INTERVAL, AND SINCE FP IS COMPUTED DIRECTLY FROM /AF/, FP IN ORDER TO CORRESPOND TO THE
033736,000147:                                                                                                  #  ACTUAL THRUST LEVEL AT THE END OF THE INTERVAL MUST BE WEIGHTED BY
033737,000148: 
033738,000149:                                                                                                  #                                    PIF(PPROCESS + TL)     PIF /PIF/
033739,000150:                                                                                                  #                          FWEIGHT = ------------------ + -------------
033740,000151:                                                                                                  #                                          PGUID          2 PGUID FRATE
033741,000152: 
033742,000153:                                                                                                  #  WHERE PPROCESS IS THE TIME BETWEEN PIPA READING AND THE START OF THROTTLING, PGUID IS THE GUIDANCE PERIOD, AND
033743,000154:                                                                                                  #  FRATE IS THE THROTTLING RATE (32 UNITS PER CENTISECOND).  PGUID IS EITHER 1 OR 2 SECONDS. THE "TL" IN THE
033744,000155:                                                                                                  #  FIRST TERM REPRESENTS THE ENGINE'S RESPONSE LAG.   HERE FWEIGHT IS COMPUTED FOR USE NEXT PASS.
033745,000156: 
033746,000157: 31,2251           31762                           CA       THISTPIP   +1                         #  INITIALIZE FWEIGHT COMP AS IF FOR P66

Note: the complete comment for the above statement has a box drawn arround it using a blue pen.

033748,000159: 31,2252           54130                           TS       BUF                                   
033749,000160: 
033750,000161: 31,2253           41010                           CS       MODREG                                #  ARE WE IN FACT IN P66?
033751,000162: 31,2254           62433                           AD       DEC66                                 
033752,000163: 31,2255           00006                           EXTEND                                         
033753,000164: 31,2256           12263                           BZF      FWCOMP                                #  YES
033754,000165: 
033755,000166: 31,2257           31234                           CA       PIPTIME    +1                         #  NO:   INITIALIZE FOR TWO SECOND PERIOD
033756,000167: 31,2260           54130                           TS       BUF                                   
033757,000168: 31,2261           35003                           CAF      4SECS                                 
033758,000169: 31,2262           12264                           TCF      FWCOMP     +1                         
033759,000170: 
033760,000171: 31,2263           35000        FWCOMP             CAF      2SECS                                 
033761,000172: 31,2264           54002                 +1        TS       Q                                     
033762,000173: 31,2265           00006                           EXTEND                                         
033763,000174: 31,2266           74746                           MP       BIT6                                  
033764,000175: 31,2267           22131                           LXCH     BUF        +1                         
033765,000176: 31,2270           40130                           CS       BUF                                   #  TIME OF LAST PIPA READING.
033766,000177: 31,2271           60025                           AD       TIME1                                 
033767,000178: 31,2272           62004                           AD       THROTLAG                              #  COMPENSATE FOR ENGINE RESPONSE LAG
033768,000179: 31,2273           74357                           MASK     LOW8                                  #  MAKE SURE SMALL AND POSITIVE
033769,000180: 31,2274           22007                           ZL                                             
033770,000181: 31,2275           00006                           EXTEND                                         
033771,000182: 

Page 789

033773,000184: 31,2276           10002                           DV       Q                                     
033774,000185: 31,2277           00006                           EXTEND                                         
033775,000186: 31,2300           71612                           MP       PIF                                   
033776,000187: 31,2301           60000                           DOUBLE                                         
033777,000188: 31,2302           53611                           DXCH     FWEIGHT                               
033778,000189: 31,2303           11612                           CCS      PIF                                   
033779,000190: 31,2304           64753                           AD       ONE                                   
033780,000191: 31,2305           12307                           TCF      +2                                    
033781,000192: 31,2306           64753                           AD       ONE                                   
033782,000193: 31,2307           00006                           EXTEND                                         
033783,000194: 31,2310           71612                           MP       PIF                                   
033784,000195: 31,2311           00006                           EXTEND                                         
033785,000196: 31,2312           10131                           DV       BUF        +1                         
033786,000197: 31,2313           22007                           ZL                                             
033787,000198: 31,2314           21611                           DAS      FWEIGHT                               
033788,000199: 
033789,000200: 
033790,000201: 31,2315           01607        THDUMP             TC       RTNHOLD                               
033791,000202: 
033792,000203: 
033793,000204:                                                                                                  #      FLATOUT THROTTLES UP THE DESCENT ENGINE, AND IS CALLED AS A BASIC SUBROUTINE.
033794,000205: 
033795,000206: 31,2316           34737        FLATOUT            CAF      BIT13                                 #  4096 PULSES
033796,000207: 31,2317           55606        WHATOUT            TS       PIFPSET                               #  USE PIFPSET SO FWEIGHT WILL BE ZERO
033797,000208: 31,2320           44755                           CS       ZERO                                  
033798,000209: 31,2321           55620                           TS       FCOLD                                 
033799,000210: 31,2322           55612                           TS       PIF                                   
033800,000211: 31,2323           00006                           EXTEND                                         
033801,000212: 31,2324           23607                           QXCH     RTNHOLD                               
033802,000213: 31,2325           12240                           TCF      DOIT                                  
033803,000214: 
033804,000215: 
033805,000216:                                                                                                  #      MASSMULT SCALES ACCELERATION, ARRIVING IN A AND L IN UNITS OF 2(-4) M/CS/CS, TO FORCE IN PULSE UNITS.
033806,000217: 
033807,000218: 31,2326           00006        MASSMULT           EXTEND                                         
033808,000219: 31,2327           22130                           QXCH     BUF                                   
033809,000220: 31,2330           52155                           DXCH     MPAC                                  
033810,000221: 31,2331           07106                           TC       DMP                                   
033811,000222: 31,2332           01243                           ADRES    MASS                                  
033812,000223: 31,2333           07106                           TC       DMP                                   #  LEAVES PROPERLY SCALED FORCE IM MPAC
033813,000224: 31,2334           02005                           ADRES    SCALEFAC                              
033814,000225: 31,2335           07262                           TC       TPAGREE                               
033815,000226: 31,2336           30154                           CA       MPAC                                  
033816,000227: 31,2337           00006                           EXTEND                                         
033817,000228: 31,2340           12343                           BZF      +3                                    
033818,000229: 31,2341           34733                           CAF      POSMAX                                
033819,000230: 31,2342           00130                           TC       BUF                                   
033820,000231: 31,2343           52156                           DXCH     MPAC       +1                         
033821,000232: 31,2344           00130                           TC       BUF                                   

Note: There is a small drawing in blue pen in the comment section of the above statements starting in the line of statement CA MPAC. The drawing resembles a linear step function.

033825,000236:                                                                                                  ##

| | | ----| | / | | / | |----/ | | | | |

033834,000245: 

Page 790

033836,000247:                                                                                                  #      CONSTANTS:-
033837,000248: 
033838,000249: 31,2345     4737               FEXTRA             =        BIT13                                 #  FEXT       +5.13309020E+4
033839,000250: 
033840,000251: 31,2345           04143        /AF/CNST           DEC      .13107                                
033841,000252: 
033842,000253:                                                                                                  #  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

End of include-file THROTTLE_CONTROL_ROUTINES.agc.  Parent file is MAIN.agc