T-Kernel Specification (1.B0.02)

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106 CHAPTER 4. T-KERNEL/OS FUNCTIONS 4.5 Extended Synchronization and Communication Functions Extended synchronization and communication functions use objects independent of tasks to realize more sophisticated synchronization and communication between tasks. The functions specified here include mutex, message buffer, and rendezvous port functions. Copyright c○ 2002, 2003 by T-Engine Forum T-Kernel 1.B0.02
4.5. EXTENDED SYNCHRONIZATION AND COMMUNICATION FUNCTIONS 107 4.5.1 Mutex A mutex is an object for mutual exclusion control among tasks that use shared resources. Priority inheritance mutexes and priority ceiling mutexes are supported, as tools for managing the problem of unbounded priority inversion that can occur in mutual exclusion control. Functions are provided for creating and deleting a mutex, locking and unlocking a mutex, and referencing mutex status. A mutex is identified by an ID number called a mutex ID. A mutex has a status (locked or unlocked) and a queue for tasks waiting to lock the mutex. For each mutex, T-Kernel keeps track of the tasks locking it; and for each task, it keeps track of the mutexes it has locked. Before a task uses a resource, it locks a mutex corresponding to that resource. If the mutex is already locked by another task, the task waits for the mutex to become unlocked. Tasks in mutex lock waiting state are put in the mutex queue. When a task finishes with a resource, it unlocks the mutex. A mutex with TA INHERIT(= 0x02) designated as mutex attribute supports priority inheritance protocol, while one with TA CEILING(= 0x03) designated supports priority ceiling protocol. When a priority ceiling mutex is created, a ceiling priority is assigned to it, indicating the base priority of the task having the highest base priority among the tasks able to lock that mutex. If a task having a higher base priority than the ceiling priority of the mutex tries to lock it, error code E ILUSE is returned. If tk chg pri is issued in an attempt to set the base priority of a task locking a priority ceiling mutex to a value higher than the ceiling priority of that mutex, E ILUSE is returned by the tk chg pri system call. When these protocols are used, unbounded priority inversion is prevented by changing the current priority of a task in a mutex operation. Strict adherence to the priority inheritance protocol and priority ceiling protocol requires that the task current priority must always be changed to match the peak value of the following priorities. This is called strict priority control. • The task base priority. • When tasks lock priority inheritance mutexes, the current priority of the task having the highest current priority of the tasks waiting for those mutexes. • When tasks lock priority ceiling mutexes, the ceiling priority of the mutex having the highest ceiling priority among those mutexes. Note that when the current priority of a task waiting for a priority inheritance mutex changes as the result of a base priority change brought about by mutex operation or tk chg pri, it may be necessary to change the current priority of the task locking that mutex. This is called dynamic priority inheritance. Further, if this task is waiting for another priority inheritance mutex, dynamic priority inheritance processing may be necessary also for the task locking that mutex. The T-Kernel specification defines, in addition to the above strict priority control, a simplified priority control limiting the situations in which the current priority is changed. The choice between the two is an implementation-dependent matter. In the simplified priority control, whereas all changes in the direction of raising the task current priority are carried out, changes in the direction of lowering that priority are made only when a task is no longer locking any mutexes. (In this case the task current priority reverts to the base priority.) More specifically, processing to change the current priority is needed only in the following circumstances. • When a task with a higher current priority than that of the task locking a priority inheritance mutex starts waiting for that mutex. • When a task waiting for a priority inheritance mutex is changed to a higher current priority than that of the task locking that mutex. • When a task locks a priority ceiling mutex having a higher ceiling priority than the task’s current priority. 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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4.6. MEMORY POOL MANAGEMENT FUNCTIO
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4.7. TIME MANAGEMENT FUNCTIONS 163
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4.8. INTERRUPT MANAGEMENT FUNCTIONS
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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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5.5. 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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