iAPX 286 Operating System Writers Guide 1983

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DATA SHARING, ALIASING, AND SYNCHRONIZATIONsegments. If there are call gates in the GDT at PL 3, then these procedures are accessible to all otherprocedures in the system.SEND_MESSAGE fills a message with the specified data and descriptors, removes the descriptorsfrom the descriptor table, and links the message at the tail of the message queue. If a task is waitingat the mailbox, SEND_MESSAGE causes it to be linked into the ready queue so that it will find themessage the next time it is scheduled to run.If RECEIVE.-MESSAGE finds no messages waiting at the mailbox, then it links"the task into a waitingqueue. The task queue threads through the task database. The task will continue executing when anothertask sends a message to the mailbox. If (or when) a message is waiting, RECEIVE_MESSAGE writesthe data portion of the message at a specified location in the receiving task's space and installs thedescriptor portion in specified slots in one of the receiving task's descriptor tables (GDT or LDT).These examples do not include management of space and queues for messages because conventionalalgorithms apply. .External procedures GELMSG~PACE, ENQUEUE_MESSAGE,DEQUEUE_MESSAGE, and FREE_MSG_SPACEprovide these functions.Special handling is required to accommodate the fact that a descriptor in a message is temporarily notin any descriptor table. There are two cases to consider: .• The descriptor is the sole descriptor for the segment. In this case, no changes can be made to thesegment because it is temporarily inaccessible. You should take care that no failure in the communicationprocess causes the descriptor to become lost. A memory area without a descriptor cannotbe freed.• The descriptor is an alias (Le., one of several descriptors for the same segment). Since the segmentis (presumably) accessible via the other aliases, it is possible for some task to request some operationon the segment during the time the descriptor in the. message is absent from any descriptor table.Normally, the operating system updates all aliases when it makes any major changes to a segment(for example, relocation or swapping to secondary storeJ~ This is not possible (given the aliasingscheme previously presented in this chapter) when the alias is not in a descriptor table. To solve theproblem, this example assumes there are two procedures;a. DISABLRALIAS..YTR that marks the alias list element to indicate to the alias manager thatthe alias is in a mailboxb. FI~LIAS..YTR that, when the message is delivered, updates the alias pointer with the newlocation of the alias and with any segment information that may have changed while the aliaswas absent from the alias list.Dynamic systems may need to create and delete mailboxes dynamically. The only difficulty in creatinga mailbox is ensuring that no task uses it while it is being constructed. (The next section considers thisproblem.) To delete a mailbox the operating system must awaken any tasks that are waiting for messages,delete any descriptors (aliases) that reside in undelivered messages, and delete the undelivered messagesthemselves.The operating system may, as part of the process of task creation, give each task at least one mailbox.If the mailbox feature is the only means of passing aliases among tasks, a task cannot receive an aliasfor a mailbox unless it already has a mailbox. Some operating system designs may require every taskto have a mailbox for such purposes as receiving memory segments from the memory-allocation module.5 .... 12 121960-001
DATA SHARING, ALIASING, AND SYNCHRONIZATIONPL/M-286 COMPILER 960-508 date PAGE 1system-ID PL/M-286 Vx.y COMPILATION OF MODULE MAILBOXOBJECT MODULE PLACED IN :Fl:MBOX.OBJCOMPILER INVOKED BY: PLM286.86 :Fl:MBOX.PLM DEBUG$ PAGEWIDTH(71) TITLE('9613-5138') INCLUDE (:Fl:NUCSUB.PLM)$ NOLIST1MAILBOX:DO;/*******************************************************//* Definitions */2 1DECLARE FAILEDOKLITERALLY 'S13130H',LITERALLY '13';/*******************************************************//* Externals */3 14 25 26 17 28 29 110 2II 212 113 214 115 216 217 118 219 2213 121 222 223 124 225 226 127 228 2NULLIFY: PROCEDURE (SLOT) EXTERNAL;DECLARE SLOT SELECTOR;END NULLIFY;STORE DESCR: PROCEDURE (SLOT,PTR) EXTERNAL;DECLARE SLOT SELECTOR,PTR POINTER;END STORE_DESCR;LOAD DESCR: PROCEDURE(PTR,SLOT) EXTERNAL;DECLARE PTR POINTER,SLOT SELECTOR;END LOAD _DESCR;DISPATCHER: PROCEDURE EXTERNAL;END DISPATCHER;ENQUEUE WAIT: PROCEDURE(QUEUE ID) EXTERNAL;DECLARE QUEUE ID SELECTOR; -END ENQUEUE_WAIT;DEQUEUE WAIT: PROCEDURE(QUEUE ID, EXCEP P) EXTERNAL;DECLARE QUEUE ID SELECTOR, EXCEP P POINTER;END DEQUEUE_WAIT; -DISABLE ALIAS PTR: PROCEDURE(SLOT) EXTERNAL;DECLARE SLOT-SELECTOR;END DISABLE_ALIAS_PTR;FIX ALIAS PTR: PROCEDURE (ALIAS_LIST_ID) EXTERNAL;DECLARE ALIAS LIST ID POINTER;END FIX_ALIAS_PTR; -GET MSG SPACE: PROCEDURE(BOX ID,MSG P P,EXCEP P)EXTERNAL;DECLARE BOX ID SELECTOR, (MSG_P_P~ EXCEP_P)-POINTER;END GET_MSG_SPACE;Figure 5·7. Example of Mailbox Procedures5-13 121960-001
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LITERATUREIn addition to the produc
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Intel Corporation makes no warranty
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PREFACEExternal LiteratureMany aspe
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Table of ContentsCHAPTER 1PageINTRO
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TABLE OF CONTENTSCHAPTER 9PageVIRTU
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TABLE OF CONTENTSLIST OF FIGURESFig
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Introduction to Protected 1Multitas
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INTRODUCTION TO PROTECTED MULTITASK
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inter INTRODUCTION TO PROTECTED MUL
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111'eI INTRODUCTION TO PROTECTED MU
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Using Hardware2Protection Features
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USING HARDWARE PROTECTION,FEATURESs
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interUSING HARDWARE PROTECTION FEAT
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USING HARDWARE PROTECTION FEATURES(
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USING HARDWARE PROTECTION FEATURES
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USING HARDWARE PROTECTION FEATUREST
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USING HARDWARE PROTECTION FEATURESo
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USING HARDWARE PROTECTION FEATURESL
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USING HARDWARE PROTECTION FEATUREST
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USING HARDWARE PROTECTION FEATURESE
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inl:el~USING HARDWARE PROTECTION FE
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IntelUSING HARDWARE PROTECTION FEAT
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IntelU~ING HARDWARE PROTECTION FEAT
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lSLDTFORMATRt;;SERV~~"O~iA~~.~ijij
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CHAPTER 3REAL MEMORY MANAGEMENTIn d
Page 61 and 62: REAL MEMORY MANAGEMENTIALLOCATEGATE
Page 63 and 64: interREAL MEMORY MANAGEMENTBEFOREAF
Page 65 and 66: REAL MEMORY MANAGEMENTGLOBAL DESCRI
Page 67 and 68: REAL MEMORY MANAGEMENTTable 3-1. Ac
Page 69 and 70: REAL MEMORY MANAGEMENTBEFOREI "FREE
Page 71 and 72: REAL MEMORY MANAGEMENTBEFOREI "FREE
Page 73 and 74: REAL MEMORY MANAGEMENTPL/M-286 COMP
Page 79: REAL MEMORY MANAGEMENTPL/M-286 COMP
Page 82 and 83: IIIIIIIIIIIIIIIIIIIIII
Page 84 and 85: II I telTASK MANAGEMENTCPUTASK REGI
Page 86 and 87: TASK MANAGEMENTIf the proc~sser, wh
Page 88 and 89: TASK MANAGEMENTUsually, termination
Page 90 and 91: TASK MANAGEMENTTASK XTSS TSS TSS TS
Page 92 and 93: TASK MANAGEMENTSCHEDULING POLICIEST
Page 94 and 95: TASK MANAGEMENTThe example in figur
Page 96 and 97: TASK MANAGEMENTREADY QUEUESBY PRIOR
Page 98 and 99: IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
Page 101 and 102: CHAPTER 5DATA SHARING, ALIASING, AN
Page 103 and 104: DATA SHARING, ALIASING, AND SYNCHRO
Page 105 and 106: interDATA SHARING, ALIASING, AND SV
Page 111: DATA SHARING, ALIASING, AND SYNCHRO
Page 117: DATA SHARING, ALIASING, AND SYNCHRO
Page 121 and 122: CHAPTER 6SIGNALS AND INTERRUPTSInte
Page 123 and 124: interSIGNALS AND INTERRUPTSlOTGOTTS
Page 125 and 126: SIGNALS AND INTERRUPTSTable 6-1. In
Page 127 and 128: SIGNALS AND INTERRUPTSSend interrup
Page 129 and 130: SIGNALS AND INTERRUPTSprocedure suc
Page 131: Handling Exception Conditions 7
Page 134 and 135: HANDLING EXCEPTION CONDITIONSError
Page 136 and 137: HANDLING EXCEPTION CONDITIONSAn exc
Page 138 and 139: HANDLING EXCEPTION CONDITIONSA few
Page 140 and 141: HANDLING EXCEPTION CONDITIONSAn ins
Page 143 and 144: CHAPTER 8INPUT /OUTPUTMany of the c
Page 145 and 146: INPUT /OUTPUTYou can still take adv
Page 147 and 148: INPUT /OUTPUT• Only the operating
Page 149: INPUT /OUTPUTtask the I/0 procedure
Page 153 and 154: CHAPTER 9VIRTUAL MEMORYThe memory l
Page 155 and 156: VIRTUAL MEMORYthose segments that a
Page 157 and 158: VIRTUAL MEMORY• Return the RAM sp
Page 159 and 160: VIRTUAL MEMORYReplacementThe operat
Page 161 and 162: System Initialization10
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CHAPTER 10SYSTEM INITIALIZATIONThe
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SYSTEM INITIALIZATIONStarting the f
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iAPX286 "ACRO ASSEMBLERLOCOBJEnter
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iAPX286 MACRO ASSEMBLEtEnter Protec
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iAPX286 MACRO ASSEMBLER·· Enter ~
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iAPX286 'UCRO USE148LER Ente,. P,.o
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iAPX286 MACRO ASSEMBLEREnt9~ P~otec
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iAPX286 MACRO ASSEMBLE~ INITIAL TAS
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CHAPTER 11BINDING AND LOADINGBindin
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BINDING AND LOADINGNamingThe names
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BINDING AND LOADING$ COMPACT (NUCLE
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interBINDING AND LOADINGsystem-IDiA
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BIND.ING AND LOADINGConverting a Pr
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BINDING AND LOADINGThe OMF of each
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interBINDING AND LOADINGsystem-IDiA
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BINDING AND LOADINGPL/M-2B6 COMPILE
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BINDING AND LOADI.NGPL/M-286 COMPIL
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BINDING AND LOADINGPL/M-286 COMPILE
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BINDING AND LOADINGPL/M-2B6 COMPILE
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BINDING AND LOAD.INGPL/M-286 COMPIL
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interBINDING AND LOADINGPL/M-286 CO
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BINDING AND LOADINGPL/M-286 COMPILE
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Numerics Processor Extension 12
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NUMERICS PROCESSOR EXTENSIONMath Pr
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interNUMERICS PROCESSOR EXTENSION
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Extended Protection13
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EXTENDED PROTECTIONIndirect NamingT
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EXTENDED PROTECTIONanother procedur
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Glossary
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GLOSSARYbootloadable module: a modu
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GLOSSARYexception: a processor-dete
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GLOSSARYintersegment reference: a r
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GLOSSARYoutward call: the attempt t
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GLOSSARYscheduling state: one of se
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GLOSSARYvirtual address: an address
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INDEXES register, 2-17, 2-18, 2-21,
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INDEXpresent bit, 2-2, 2-3, 2-9, 5-
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interu.s. SALES OFFICESALAIWIA IlEQ
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interu.s. DISTRIBUTORSNEW YORK (C"n
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intJINTEL INTERNATIONAL SALES OFFIC
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