Assembly listing generated by yaYUL

Source Code

These source-code files are part of a reconstructed copy of Skylark 048, the Block II Command Module (CM) Apollo Guidance Computer (AGC) software for the Skylab-2, Skylab-3, Skylab-4, and Apollo-Soyuz Test Project missions.

They have been created via disassembly of binary dumps of the original core rope memory modules actually flown on Skylab-2, part numbers 2010802-541, 2010802-551, 2010802-561, 2010802-571, 2010802-581, and 2010802-591. Access to these modules was provided by the New Mexico Museum of Space History, who we are much indebted to.

The source code for the Apollo 15, 16, and 17 software, Artemis 072, was used as a starting point. Heavy use was made of TRW 4900.5-244, Programmed Guidance Equations for Skylark Command Module Earth Orbital Program, dated 14 February 1972. This document contains pseudocode of essentially all of Skylark, using original program labels which have been copied for this source reconstruction.

Since only binary dumps (rather than listings) of Skylark are available as source material, all comments and labels are approximate. They have been taken from the Programmed Guidance Equations or other AGC programs where possible, or, in some places, written from scratch to match what we believe would have been in the original listing.

019759,000002: 019760,000003: 019761,000004: 019762,000005: 019763,000006: 019764,000007: 019765,000008: 019766,000009: 019767,000010: 019768,000011: 019769,000012: 019770,000013: 019771,000014: 019772,000015: 019773,000016: 019774,000017: 31,2000 019775,000018: 31,2000 019776,000019: 019777,000020: 31,2000 019803,000046: 019804,000047: 31,2027 019805,000048: 31,2030 ## Copyright: Public domain. ## Filename: R31.agc ## Purpose: A section of Skylark revision 048. ## It is part of the source code for the Apollo Guidance Computer (AGC) ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of ## this software are available; instead, this file was created via ## disassembly of dumps of the core rope modules actually flown on ## Skylab-2. Access to these modules was provided by the New Mexico ## Museum of Space History. ## Assembler: yaYUL ## Contact: Ron Burkey <info@sandroid.org>. ## Website: www.ibiblio.org/apollo/index.html ## Mod history: 2023-09-04 MAS Created from Artemis 072. ## 2024-03-05 MAS Updated for Skylark 48. SETLOC R31 BANK COUNT* $$/R3134 C">019778,000021: 31,2000 35057 R31CALL CAF PRIO3 05150 TC FINDVAC EBANK= SUBEXIT 02031 62064 2CADR V83CALL 159">019783,000026: 31,2004 04647 DSPDELAY TC BANKCALL 01730 CADR 1SECDELY 31237 CA EXTVBACT 74766 MASK BIT12 00006 EXTEND 12004 BZF DSPDELAY 8">019790,000033: 31,2012 30105 DISPN5X CA FLAGWRD9 # TEST R31FLAG (IN SUNDANCE R31FLAG WILL 74776 MASK R31FLBIT # ALWAYS BE SET AS R34 DOES NOT EXIST 00006 EXTEND 12020 BZF +3 32135 CAF V16N54 # R31 USE NOUN 54 02021 TC +2 32136 CAF V16N53 # R34 USE NOUN 53 04647 TC BANKCALL 20456 CADR GOMARKF 05601 TC B5OFF 05601 TC B5OFF 12012 TCF DISPN5X 31,2026 06006 V83 TC INTPRET 77650 GOTO 62175 HAVEBASE # INTEG STATE VECTORS C">019806,000049: 31,2031 06006 V83CALL TC INTPRET 77650 GOTO 62144 STATEXTP # EXTRAPOLATE STATE VECTORS 350">019809,000052: 31,2034 52375 COMPDISP VLOAD VSU 00001 RATT 02210 RONE 51406 PUSH ABVAL # RATT-RONE TO 0D PD= 6 02202 STORE RANGE # METERS B-29 77301 NORM VLOAD 00047 X1 # RATT-RONE PD= 0 77762 VSR1 53457 VSL* UNIT 20201 0,1 52315 PDVL VSU # UNIT(LOS) TO 0D PD= 6 00007 VATT 02216 VONE 77641 DOT # (VATT-VONE).UNIT(LOS) PD= 0 77752 SL1 36204 STCALL RRATE # RANGE RATE M/CS B-7 47471 CDUTRIG # TO INITIALIZE FOR *NBSM* 77624 CALL 62267 R34LOS # NOTE. PDL MUST = 0. >019828,000071: 31,2057 53575 R34ANG VLOAD UNIT 02210 RONE 77715 PDVL # UR TO 0D PD= 6 15202 THISAXIS # UNITX FOR CM, UNITZ FOR LM 77214 BON VLOAD # CHK R31FLAG. ON=R31 THETA, OFF=R34 PHI 04713 R31FLAG 62067 +2 # R31-THETA 00015 12D 77624 CALL 47625 *NBSM* 41505 VXM PUSH # UXORZ TO 6D PD=12D 01720 REFSMMAT 72431 VPROJ VSL2 00001 0D 53445 BVSU UNIT 00007 6D 47315 PDVL VXV # UP/2 TO 12D PD=18D 02210 RONE 02216 VONE 47256 UNIT VXV 02210 RONE 63241 DOT PDVL # SIGN TO 12D, UP/2 TO MPAC PD=18D 00015 12D 50372 VSL1 DOT # UP.UXORZ 00007 6D 72565 SIGN SL1 00015 12D 77726 ACOS 26206 STOVL RTHETA 02210 RONE 51041 DOT BPL 00007 6D 62124 +5 44345 DLOAD BDSU # IF UXORZ.R NEG, RTHETA = 1 - RTHETA 02206 RTHETA 15212 DPPOSMAX 02206 STORE RTHETA # RTHETA BETWEEN 0 AND 1 REV. 77776 +5 EXIT 34775 CAF BIT5 # HAVE WE BEEN ANSWERED 71237 MASK EXTVBACT 00006 EXTEND 12137 BZF ISITP37 41237 CS EXTVBACT 74766 MASK BIT12 27237 ADS EXTVBACT 12026 TCF V83 >019876,000119: 31,2135 04066 V16N54 VN 1654 >019877,000120: 31,2136 04065 V16N53 VN 1653 7">019878,000121: 31,2137 05367 ISITP37 TC CHECKMM 00045 MM 37 B-14 15537 TCF ENDEXT # NO, DIE 05542 TC CLEARMRK 14105 TCF MNKGOPOO # STATEXTP DOES AN INITIAL PRECISION EXTRAPOLATION OF THE # LEM STATE VECTOR TO PRESENT TIME OR TO PIPTIME IF AV G # IS ON AND SAVES AS BASE VECTOR. IF AV G IS ON RN + VN # ARE USED AS THE CM STATE VECTOR AND THE INITIAL R RDOT # RTHETA ARE COMPUTED WITH NO FURTHER INTEGRATION. IF AV # G IS OFF A PRECISION EXTRAPOLATION IS MADE OF THE CM # STATE VECTOR TO PRESENT TIME AND..... # THE CM + LM STATE VECTORS ARE INTEGRATED TO PRES TIME # USING PRECISION OR CONIC AS SURFFLAG IS SET OR CLEAR. # IF AV G IS ON THEN SUBSEQUENT PASSES WILL PROVIDE # USE OF RN + VN AS CM STATE VECTOR AND THE LM STATE # VECTOR WILL BE PRECISION INTEGRATED USING LEMPREC # IF SURFFLAG IS SET. # CM STATE VECTOR RONE VONE + LM STATE VECTOR RATT # VATT ARE USED IN COMPUTING R RDOT RTHETA. 450">019901,000144: 31,2144 43034 STATEXTP RTB BOF # INITIAL INTEGRATION 45563 LOADTIME 03751 V37FLAG 62152 BOTHGO # AV G OFF, USE PRESENT TIME 77624 CALL 62251 GETRVN # ON, USE RN, VN, PIPTIME >019907,000150: 31,2152 02224 BOTHGO STORE BASETIME 34041 STCALL TDEC1 11414 LEMPREC 77775 VLOAD # BASE VECTOR, LM 00017 RATT1 26126 STOVL BASEOTP # POS. 00025 VATT1 02142 STORE BASEOTV # VEL. 71214 BON DLOAD 03711 V37FLAG 62034 COMPDISP # COMPUTE R RDOT RTHETA FROM # RONE(RN) VONE(VN) RATT+VATT(LEMPREC) 00015 TAT 34041 STCALL TDEC1 11400 CSMPREC 77775 VLOAD # BASE VECTOR, CM 00017 RATT1 26156 STOVL BASETHP # POS. 00025 VATT1 02226 STORE BASETHV # VEL. 345">019927,000170: 31,2175 47014 HAVEBASE BON RTB # SUBSEQUENT INTEGRATIONS 03711 V37FLAG 62242 GETRVN5 45563 LOADTIME 34041 STCALL TDEC1 # AV G OFF. SET INTEG. OF CM 11720 INTSTALL 77775 VLOAD 02156 BASETHP 25535 STOVL RCV 02226 BASETHV 15543 STODL VCV 02224 BASETIME 77614 SET 01473 INTYPFLG 35517 STCALL TET 11444 INTEGRVS # INTEGRATION --- AT LAST--- 77775 VLOAD 00001 RATT 26210 STOVL RONE 00007 VATT 16216 STODL VONE # GET SET FOR CONIC EXTRAP.,OTHER 00015 TAT 77624 CALL 11720 INTSTALL # LEMCONIC IF NOT DOWN 77614 SET 01473 INTYPFLG >019953,000196: 31,2227 00041 OTHINT STORE TDEC1 # ENTERED IF AV G ON TO INTEG LM 77775 VLOAD 02126 BASEOTP 25535 STOVL RCV 02142 BASEOTV 15543 STODL VCV 02224 BASETIME 35517 STCALL TET 11444 INTEGRVS 77650 GOTO 62034 COMPDISP # COMPUTE R RDOT RTHETA 5">019964,000207: 31,2242 77624 GETRVN5 CALL # AV G ON 62251 GETRVN 77624 CALL 11720 INTSTALL 52014 CLEAR GOTO # INTEGRVS (PREC) IF LM NOT DOWN 01673 INTYPFLG 62227 OTHINT >019971,000214: 31,2251 77620 GETRVN STQ 00000 0D 52175 VLOAD GOTO # AV G ON, RONE = RN VONE = VN 01022 RN # AND USE PIPTIME 62256 +1 36210 STCALL RONE 62260 +1 52175 VLOAD GOTO 01030 VN 62263 +1 16216 STODL VONE 01036 PIPTIME 77650 GOTO 00000 0D SETLOC R34 BANK COUNT* $$/R3134 >019988,000231: 31,2267 77776 R34LOS EXIT 30036 CA CDUS 50120 INDEX FIXLOC 54011 TS 9D 30035 CA CDUT 50120 INDEX FIXLOC 54013 TS 11D 30120 CA FIXLOC 66211 AD SIX 40000 COM 50120 INDEX FIXLOC 54046 TS X1 06006 TC INTPRET 77624 CALL 46000 SXTNB 34015 STCALL 12D 62057 R34ANG Parent file is MAIN.agc