A COMMAND & DATA SUBSYSTEM FOR DEEP SPACE EXPLORATION BASED ON THE RCA 1802 MICROPROCESSOR IN A DISTRIBUTED CONFIGURATION Jack S. Thomas California Institute of Technology Jet Propulsion Laboratory Pasadena, California The Command and Data Subsystem (CDS) is an RCA 1802 CMOS microprocessor-based subsystem that acts as the central nervous system for the Galileo Orbiter Spacecraft. All Communication between the ground and spacecraft flows through the CDS. The CDS also distributes commands in real time, algorithmetically expanded from a data base loaded from the ground and in response to spacecraft alarms. The distributed microprocessor system is configured as a redundant set of hardware with three microprocessors on each half. The microprocessors are surrounded by a group of special purpose hardware components which greatly enhance the ability of the software to perform its task. The presenter shows how the software architecture makes a distributed system of six microprocessors appear to each user as a single virtual machine, and collectively as a set of cooperating virtual machines that prevent the simul- taneous presence of the several users from interfering destructively with each other. 17 u u_ O 18 GALILEO CDS FLIGHT HARDWARE CONFIGURATION STRING-A, PRIME STRING-B, BACKUP un HCP , ' 1A, IB -1 f - < f HLM1A 1802 HLM1B 1802 32 KB 32 KB | BC | | BC | CC/DC TO f DSB-A DSB-B J PPS, RFS -^ 1• LLM1A "T^ LLM1B J MDS ENGR —11802 ^- DATA LOW Tb |l6 KB — ' 16 KBLL1 DATA RATE ^^T -| TFI FMFTBY ~~" C 1 I | AACS | CRITICAL ENABLES ^ rsc ^ _ CONFIG CONTROL -* VA 10 IA, IB | MAG^ | MEM PROTECT -^ J GOLAY _e 1 — T_ GOLAY 1 CODE 1A 7~° — CODE IB 1 | PWS | - DBUM 1A r (REQ8 KB | DDS~[ DMS • (TAPE) J. \ [ EPD~| DBUM IB ^_ —^>*- (R/T) 8 KB SSI BUM 1A r- ~^-°~ BUM1B PWS 16 KG 16 KB 16 KB 0 "sol "i^ " |fs Q -1 HI RATE «^o-"^~~ ^ 1 SHUN DESPUN CC/DC TO f LLM2A J ENGR PPS ^~T LLM 2B -1 TS 1802 |— ^ ENGR DATA *" — _^ 1802 I TS ^ ' DAT/^ IUS, STS ^T" L 1-| TELEMFTRY ^^ 1 1 | SSI "| CRITICAL i | uys | CONFIG CONTROL -* 2A> 2B "* | NIMS | MEM PROTECT -+ J | PPR~~] 19 GALILEO CDS FLIGHT SOFTWARE ARCHITECTURE I UNKNOWN RESOURCE UTILIZATION EXCEPT BY LIMITED KNOWN RESOURCE UTILIZATION | GROUND FUNCTIONAL MODELING UNRESTRICTED ACCESS RESTRICTED ACCESS 10 CONCURRENT 10 . 16 CONCURRENT PROGRAMS 32 SINGLE ADMINISTRATIVE CONCURRENT I STATIC REAL TIME CONCURRENT PGM CONSTRAINT CHECKED INSTRUCTION PROGRAMS F/P PROGRAMS PROGRAMS } PROGRAMS WITH STATIC PARAMETERS COOPERATING VIRTUAL MACHINES > SHARE FUNCTIONAL COMMANDS CYCLE SERIALLY I/MINOR FRAME FUNCTIONAL COMMAND INTERPRETER ROUTINES \ VARIABLES FOR ALL PROGRAMS RESTRICTED MUTUALLY WRITE ACCESS EXCLUSIVE HLM PROCESSOR TIME ALLOCATION 1. FOREGROUND EXECUTIVE 2. ADMINISTRATIVE PROGRAMS 3. IMMEDIATE ACTION COMMAND PROGRAM 4. FAULT PROTECTION PROGRAMS 5. ENGINEERING SEQUENCE PROGRAMS 6. SCIENCE SEQUENCE PROGRAMS 7. DELAYED ACTION COMMAND PROGRAMS 8. PROCESSOR TIME MARGIN 1 I l i l i 1 1 1 2 1 2 ',3 4 L4| 5 15| 6 1 6 |7l8 8 8 8 8 8 i i i 1 l 1 1 i i i i i i RTI 0 RTI 1 RTI 2 RTI 3 RTI 4 RTI 5 RTI 6 RTI 7 RTI 8 RTI 9 RT 0 1 MINOR FRAMF 2/3 SECONDS 20.