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.TITLE ^^MSX-11\\ ^SYSTEM ^SPECIFICATION
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<MSX-11 ^DISTRIBUTED ^OPERATING ^SYSTEM
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^INTRODUCTION:
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<MSX-11 IS AN EXAMPLE OF A DISTRIBUTED
EXECUTIVE AND OF A MULTIPROGRAMMING EXECUTIVE SHOWING HOW, ON
ONE <CPU TYPE, SOME OF THE ISSUES OF DISTRIBUTED PROCESSING
CAN BE ADDRESSED.
^THE <MSX-11 SYSTEM ADDRESSES THE ISSUES OF:
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*#^SUPPORT OF APPLICATIONS WITH UP TO A MODERATE NUMBER (255 OR LESS)
OF <CPU\S EXECUTING PARTS OF THE APPLICATION. ^THIS INCLUDES THE
PROVISION OF A METHOD OF INTERTASK COMMUNICATION WHICH DOES NOT
REQUIRE THE TASKS TO KNOW WHERE THE OTHER TASKS THEY ARE COMMUNICATING
WITH ARE LOCATED, IN ADDITION TO CAPABILITIES FOR SUPPORT OF SHARED
MEMORY WITHIN A <CPU.
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*#^SUPPORT OF DYNAMIC ASSIGNMENT OF A PROCESSOR WHENEVER A TASK IS
INITIATED IN THE SYSTEM;
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*#^PROVISION OF CAPABILITIES TO PERMIT RECONFIGURATION OF THE SYSTEM
AND RECOVERY FROM ERRORS OR FAILURES OF PART OF THE SYSTEM;
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*#^SUPPORT FOR PROGRAM DEVELOPMENT AND SELF-EMULATION OF THE SYSTEM
PERMITTING IT TO SIMULATE VARIOUS INTERCONNECTIONS OF A SYSTEM
WITHOUT NEED TO BUILD SPECIAL HARDWARE.
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*#^REAL TIME INTERNAL ARCHITECTURE. ^THE <MSX SYSTEM IS DESIGNED TO
SUPPORT UP TO 3.8 MEGABYTES OF MEMORY ON A <PDP11 WITH A GENERAL
"REAL-TIME" OPERATION PHILOSOPHY. ^IT WILL EITHER PERFORM A SERVICE
FOR THE CALLER APPLICATION AT ONCE, OR SIGNAL IT CANNOT AND ALLOW
RETRY. ^THE SYSTEM IS DESIGNED FOR HIGH THROUGHPUT, WITHIN THE
LIMITATIONS OF THE HARDWARE. ^IT IS WRITTEN IN ASSEMBLY LANGUAGE
AND ADDRESSES MEMORY MAPPING TO ALLOW ENOUGH OF EACH PROCESSOR TO
APPLICATIONS TO BE USEFUL.
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<MSX-11 IS WRITTEN IN <PDP11 ASSEMBLY LANGUAGE AND COMMENTED
TO ALLOW ITS STRUCTURE TO BE VISIBLE TO THE READER.
^AS SUCH, IT CAN BE USED AS AN EXAMPLE WHERE ONE CONSIDERS
DESIGNING AN OPERATING SYSTEM OF SIMILAR AIMS, EITHER
FOR OTHER PROCESSORS (I.E., IN A DIFFERENT
ASSEMBLY LANGUAGE) OR IN <HOL\S, SHOWING WHAT A SCHEDULER
LOOKS LIKE, WHAT FUNCTIONS ARE NEEDED TO PROVIDE DIFFERENT
FEATURES OF A PROCESSING ENVIRONMENT, AND HOW INTER-<CPU
MESSAGES MAY BE DEALT WITH.
<MSX IS COMMENTED EXTENSIVELY IN ORDER TO MAKE IT A
USABLE EDUCATIONAL TOOL.
^ALTHOUGH <MSX IS TOO SIMPLE FOR A
LARGE (32 BIT) MACHINE, IT CAN BE USED
AS A REFERENCE OF A SYSTEM
ON A SIMPLE COMPUTER WITH A RELATIVELY UNCOMPLICATED,
BUT HOPEFULLY COMPLETE, SET OF CAPABILITIES.
^LARGER SYSTEMS WOULD
NEED AT LEAST ITS FUNCTIONALITY. ^IT IS POSSIBLE THAT <MSX
COULD BE MADE TO HOST ONE OR MORE <HOL'\S CODE, TOO, AND
IF THAT WERE DONE, THEN <MSX COULD BE A DISTRIBUTED TEST
BASE FOR SOFTWARE DEVELOPED IN THAT LANGUAGE, AND IT WOULD
NOT MATTER THAT <MSX WILL ONLY WORK ON <PDP11 PROCESSORS.
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^COMPLETE SOURCE CODE AND DOCUMENTS ARE AVAILABLE FOR <MSX-11
FROM ^GLENN ^EVERHART, 206-1, <RCA, ^CHERRY ^HILL, ^N.^J.
08358, TELEPHONE 338-6022. ^A SIMPLE DEMONSTRATION OF SOME OF
ITS CAPABILITIES HAS BEEN PREPARED AT THE <RCA ^MOORESTOWN
FACILITY ON THE <SDF THERE ALSO.
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^OVERVIEW:
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^THE <MSX-11 OPERATING SYSTEM HAS BEEN DEVISED FOR <PDP11
<CPU\S TO ADDRESS THE PROBLEM OF CREATING AN ENVIRONMENT
FOR APPLICATIONS PROBLEMS PERMITTING THEM TO BE RUN
ON SEVERAL <CPU\S WITH DYNAMIC <CPU ASSIGNMENT AND
LOCATION INDEPENDENT COMMUNICATION BETWEEN PARTS OF THE
APPLICATIONS. ^IT IS SUITABLE FOR A VARIETY OF TYPES
OF INTERCONNECTION AND HAS SUFFICIENT CAPABILITY TO ADDRESS
UP TO 255 PROCESSORS, EACH OF WHICH MAY HAVE SEVERAL
ACTIVE PROGRAMS IN IT. ^EACH OF THE PROCESSORS MAY HAVE
UP TO 3.8 MEGABYTES MANAGED BY THE SYSTEM, WHICH OCCUPIES
ROUGHLY 16^K WORDS ITSELF.
<MSX ALSO ATTEMPTS TO PROVIDE FOR ERROR  RECOVERY AND
TO ALLOW APPLICATIONS TO BE WRITTEN IN SUCH A WAY THAT
IF PART OF THE SYSTEM GOES  DOWN, THE APPLICATIONS
MAY BE RUN WITHOUT CHANGE ON THE REMAINING PARTS. ^DETECTING
A FAILED <CPU REQUIRES ADDITION OF ROUTING/WATCHDOG
TASKS, BUT THESE ARE ORDINARY APPLICATION LEVEL TASKS
THAT DO NOT NEED TO BE A PART OF THE SYSTEM PROPER, THOUGH
THEY WOULD MOST EFFICIENTLY WORK BY HAVING ACCESS TO SYSTEM
DATA AREAS.
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<MSX ASSUMES THAT APPLICATIONS TO BE RUN UNDER ITS  CONTROL
ARE BROKEN INTO SEPARATE "TASKS" WHICH COMMUNICATE WITH EACH
OTHER VIA MESSAGES AND EACH OF WHICH MAY PERFORM ^I/^O
ACTIVITY (READS AND WRITES). ^IT ALLOWS TASKS TO BE RELOCATED
AT THEIR INITIATION BY SELECTING THE <CPU WHERE THE TASK WILL
RUN DYNAMICALLY BASED ON INFORMATION AVAILABLE TO EACH
<CPU OF THE SYSTEM. ^THE INITIAL ALGORITHM SELECTS THE <CPU
WITH THE FEWEST ACTIVE TASKS, BUT THE ALGORITHM IS SPLIT OFF
FROM THE REST OF THE SYSTEM SO THAT THE LOWEST-LEVEL PART
MAY BE ALTERED TO FIT THE APPLICATION. ^LOGIC TO PERMIT
SHARING OF MEMORY WITH OTHER TASKS IS SPECIFIED, AND NEEDS
ONLY THIS LOWEST LEVEL CODE TO BE INCLUDED. ^TASK LOADING
LOGIC ALSO EXISTS IN THE SYSTEM.
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^SINCE NOTHING AT THE TASK LEVEL KNOWS WHICH <CPU WILL BE
USED FOR AN APPLICATION, ALL <MSX APPLICATIONS MAY RUN
ON A SYSTEM WHICH HAS LOST SOME OF ITS <CPU\S. ^EACH
<CPU UNDER <MSX MAY RUN AS MANY TASKS AS WILL FIT INTO ITS
MEMORY, AND A FAILED <CPU, ONCE DETECTED BY A WATCHDOG TASK,
CAN BE MARKED UNAVAILABLE AND ALL TASKS RUNNING THERE SIMPLY
ABORTED BY THE WATCHDOG. ^THEY CAN THEN BE RESTARTED IF THE
CALLER DESIRES, AND WILL AUTOMATICALLY BE PLACED IN A <CPU
ABLE TO HANDLE THEM. ^THE <MSX SYSTEM MAINTAINS A TASK
HIERARCHY. ^THIS MEANS THAT IF A TASK IS REQUESTED BY ANOTHER
TASK, THE CALLER TASK WILL BE NOTIFIED IF THE CALLED TASK
EXITS FOR ANY REASON. ^IT ALSO MEANS THAT IF A CALLED TASK
IS ABORTED, IT IS GIVEN A "LAST CHANCE" ENTRY TO ALLOW IT
TO CLEAN UP. ^THUS, WHERE A CALLED TASK HAS FAILED, PERHAPS
DUE TO FAILURE OF THE <CPU WHERE IT WAS RUNNING, THE CALLER
CAN DECIDE FROM THE FAIL STATUS WHETHER IT SHOULD BE RESTARTED.
^MESSAGES TO A FAILED TASK WILL BE ACKNOWLEDGED WHERE POSSIBLE
(THAT IS, WHEN THE <CPU OF THE RECEIVER TASK IS STILL FUNCTIONING),
AND THE SYSTEM PROVIDES A WAY TO WAIT FOR THEIR COMPLETION THAT
WILL FALL THROUGH IF THE CALLED TASK EXITS. ^THIS IS ABOUT
AS GENERAL A SCHEME AS CAN WORK, SINCE THE POLICY ABOUT TASK
RESTART DEPENDS ON THE APPLICATION DESIGN. ^THIS SET OF
SERVICES WILL ALLOW A SYSTEM TO HAVE PARTIALLY FAILED AND STILL
PERMIT FUNCTIONS TO CONTINUE TO BE EXECUTED IN THE REST.
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<MSX WILL FUNCTION EITHER STAND-ALONE AS THE SOLE OPERATING SYSTEM
ON ITS <CPU, OR IT WILL WORK AS A TASK UNDER <RSX11M. ^IN THE SECOND
FORM, <MSX CAN ALLOW EASY PROGRAM DEVELOPMENT AND TESTING FOR
APPLICATION CODE. ^IN THE STAND-ALONE FORM, <MSX COMES WITH A
SYMBOLIC DEBUGGER TO ALLOW TESTING UNDER THE STANDALONE SYSTEM.
^IN EITHER CASE, THE APPLICATIONS PROGRAMS LOOK THE SAME, SO
THAT <MSX CAN EMULATE A DISTRIBUTED SYSTEM UNDER <RSX IN A SINGLE
<PDP11 (WITH  SEVERAL <RSX TASKS, EACH REPRESENTING AN ENTIRE
<MSX <CPU WITH ALL ITS <MSX TASKS) AND AVOID THE UNCERTAINTIES
OF HARDWARE DEVELOPMENT. ^THE APPLICATIONS SOFTWARE CAN BE
DEBUGGED UNDER THE EMULATED SYSTEM, THEN MOVED TO THE REAL ONE
AS THE REAL HARDWARE IS DEBUGGED. ^IN THIS WAY, <MSX CAN BE
A DEVELOPMENT TOOL. <MSX IS ALSO DESIGNED TO PERMIT IT TO
BE EXTENDED FOR MULTILEVEL SECURITY. ^IT CAN BE DEVELOPED
ALONG THESE LINES, SINCE IT IS A SIMPLE EXECUTIVE (DONE BY 1
PERSON) WHICH IN THE TRUE STANDALONE SYSTEM CAN COMPLETELY
ISOLATE TASKS FROM EACH OTHER AND THE SYSTEM AND REGULATE ALL
COMMUNICATIONS BETWEEN THEM. ^NO CODE TO DO THIS HAS
YET BEEN ADDED TO <MSX EXCEPT SOME SIMPLE PRIVILEGE AND ADDRESS
CHECKING LOGIC, THOUGH DESIGNS HAVE BEEN DONE FOR MORE.