T-Kernel Specification (1.B0.02)

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140 CHAPTER 4. T-KERNEL/OS FUNCTIONS is assumed that the message area designated with tk cal por will be used as a buffer in implementing tk fwd por. If cmsgsz is larger than maxrmsz of the rendezvous port before forwarding, error code E PAR is returned(See Additional Note for details). It is not necessary to issue tk fwd por and tk rpl rdv from a task-independent portion, but it is possible to issue these system calls from dispatch disabled or interrupts disabled state. This capability can be used to perform processing that is inseparable from tk fwd por or tk rpl rdv. Whether or not error checking is made for issuing of these system calls from a task-independent portion is implementationdependent. When as a result of tk fwd por Task Y that was in WAIT state for rendezvous completion reverts to WAIT on rendezvous call, the timeout until rendezvous establishment is always treated as Wait forever (TMO FEVR). The rendezvous port being forwarded to may be the same port used for the previous rendezvous (the rendezvous port on which the rendezvous designated in rdvno was established). In this case, tk fwd por cancels the previously accepted rendezvous. Even in this case, however, the call message and calptn parameters are changed to those passed to tk fwd por by the accepting task, not those passed to tk cal por by the calling task. It is possible to forward a rendezvous that has already been forwarded. [Additional Notes] A server task operation using tk fwd por is illustrated in Figure 4.8. Generally tk fwd por is executed by server distribution tasks (tasks for distributing server-accepted processing to other tasks) as shown in Figure 4.8. Accordingly, a server distribution task that has executed tk fwd por must go on to processing for acceptance of the next request regardless of whether the forwarded rendezvous is established or not. The tk fwd por message area in this case is used for processing the next request, making it necessary to ensure that changes to the contents of this message area will not affect the previously forwarded rendezvous. For this reason, after tk fwd por is executed, it must be possible to modify the contents of the message area indicated in msg passed to tk fwd por even before the forwarded rendezvous is established. In order to fulfill this requirement, in implementation it is allowed to use the message area designated with tk cal por as a buffer. That is, in the tk fwd por processing, it is permissible to copy the call messages designated with tk fwd por to the message area indicated in msg when tk cal por was called, and for the task calling tk fwd por to change the contents of the message area. When a rendezvous is established, the message placed in the tk cal por message area is passed to the accepting task, regardless of whether the rendezvous is one that was forwarded from another port. The following specifications are made to allow this sort of implementation to be used. • If there is a possibility that a rendezvous requested by tk cal por may be forwarded, a memory space of at least maxrmsz bytes must be allocated starting from msg (passed to tk cal por), regardless of the expected reply message size. • The send message size cmsgsz passed to tk fwd por must be no larger than maxrmsz of the rendezvous port before forwarding. • If a rendezvous is forwarded using tk fwd por, maxrmsz of the destination port rendezvous must not be larger than maxrmsz of the port before forwarding. Copyright c○ 2002, 2003 by T-Engine Forum T-Kernel 1.B0.02
4.5. EXTENDED SYNCHRONIZATION AND COMMUNICATION FUNCTIONS 141 Requesting Task X Extended SVC ✛ ??? ??? tk cal por SVC accept port ❄ tk acp por Server distribution tasks ❄ WAIT on rendezvous call or for completion Preprocessing ❄ ❄ ❄ tk fwd por tk fwd por tk fwd por ✲ Process A server port Process B server port Process C server port tk acp por tk acp por tk acp por ✻ ❄ ✻ ❄ ✻ ❄ Process A Process B Process C Server Server Server Task Task Task ✛ ❄ ❄ ❄ tk rpl rdv tk rpl rdv tk rpl rdv • Bold outlines indicate rendezvous ports (rendezvous entries) • While it is possible to use tk cal por in place of tk fwd por, this results in rendezvous nesting. Assuming it is acceptable for requesting Task X to resume execution after the processing of server tasks A to C is completed, use of tk fwd por does away with the need for rendezvous nesting and results in more efficient operations. Figure 4.8: Server Task Operation Using tk fwd por [Rationale for the Specification] The tk fwd por specification is designed not to require logging a history of rendezvous forwarding, so as to reduce the number of states that must be kept track of in the system as a whole. Applications that require such a log to be kept can use nested pairs of tk cal por and tk acp por rather than using tk fwd por. Copyright c○ 2002, 2003 by T-Engine Forum T-Kernel 1.B0.02
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T-Kernel Specification T-Kernel 1.B
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Contents 1 T-Kernel Overview 1 1.1
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CONTENTS v tk set flg (Set Event Fl
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CONTENTS vii 5.2.2 Address Space Ch
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CONTENTS ix td cal que (Reference Q
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List of Figures 1.1 Position of T-K
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List of Tables 2.1 State Transition
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System Call Notation In the parts o
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Index of T-Kernel/OS System Calls T
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INDEX OF T-KERNEL/OS SYSTEM CALLS x
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Index of T-Kernel/SM Extended SVC L
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Index of T-Kernel/DS System Calls T
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Chapter 1 T-Kernel Overview 1.1 Pos
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1.2. SCALABILITY 3 • Middleware m
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Chapter 2 Concepts Underlying the T
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2.2. TASK STATES AND SCHEDULING RUL
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2.2. TASK STATES AND SCHEDULING RUL
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2.3. INTERRUPT HANDLING 11 preceden
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2.5. SYSTEM STATES 13 Transient sta
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2.7. MEMORY 15 which the upper and
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Chapter 3 Common T-Kernel Specifica
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3.2. SYSTEM CALLS 19 /* * Common co
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3.2. SYSTEM CALLS 21 Ordinarily a f
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3.3. HIGH-LEVEL LANGUAGE SUPPORT RO
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Chapter 4 T-Kernel/OS Functions Thi
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4.1. TASK MANAGEMENT FUNCTIONS 27 t
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4.2. TASK-DEPENDENT SYNCHRONIZATION
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4.3. TASK EXCEPTION HANDLING FUNCTI
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4.4. SYNCHRONIZATION AND COMMUNICAT
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4.9. SYSTEM MANAGEMENT FUNCTIONS 19
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4.10. SUBSYSTEM MANAGEMENT FUNCTION
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Chapter 5 T-Kernel/SM Details of th
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5.1. SYSTEM MEMORY MANAGEMENT FUNCT
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5.2. ADDRESS SPACE MANAGEMENT FUNCT
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5.2. ADDRESS SPACE MANAGEMENT FUNCT
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5.3. DEVICE MANAGEMENT FUNCTIONS 22
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5.4. INTERRUPT MANAGEMENT FUNCTIONS
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5.5. IO PORT ACCESS SUPPORT FUNCTIO
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5.7. SYSTEM CONFIGURATION INFORMATI
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5.7. SYSTEM CONFIGURATION INFORMATI
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5.8. SUBSYSTEM AND DEVICE DRIVER ST
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260 CHAPTER 6. T-KERNEL/DS FUNCTION
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284 CHAPTER 7. REFERENCE INT tevptn
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286 CHAPTER 7. REFERENCE ER ercd =
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288 CHAPTER 7. REFERENCE INT ct = t
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290 CHAPTER 7. REFERENCE E OACV ERC
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T-Kernel Specification (1.B0.02)

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