T-Kernel Specification (1.B0.02)

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246 CHAPTER 5. T-KERNEL/SM See the device driver specifications for event details. Measures must be taken so that if event notification cannot be sent because the message buffer is full, the lack of notification will not adversely affect operation on the receiving end. One option is to hold the notification until space becomes available in the message buffer, but in that case other device driver processing should not, as a rule, be allowed to fall behind as a result. Processing on the receiving end should be designed to the extent possible to avoid message buffer overflow. 5.3.7 Device Suspend/Resume Processing Device drivers suspend and resume device operations in response to the issuing of suspend/resume (TDV SUSPEND/TDV RESUME) events to the event handling function (eventfn). Suspend and resume events are issued only to physical devices. TDV SUSPEND: Suspend Device evttyp = TDV SUSPEND evtinf = NULL (none) Suspension processing takes place in the following steps. (A) If there is a request being processed at the time, the device driver waits for it to complete, pauses it or aborts. Which of these options to take depends on the device driver implementation. Since the suspension must be effected as quickly as possible, however, pause or abort should be chosen if completion of the request will take time. Suspend events can be issued only for physical devices, but the same processing is applied to all logical devices included in the physical device. Pause: Processing is suspended, then continues after the device resumes operation. Abort: Processing is aborted just as when the abort function (abortfn) is executed, and is not continued after the device resumes operation. (B) New requests other than a resume event are not accepted. (C) The device power is cut and other suspension processing is performed. Abort should be avoided if at all possible because of its effects on applications. It should be used only in such cases as long input waits from a serial port, or when interruption would be difficult. Normally it is best to wait for completion of a request or, if possible, choose pause (suspension and resumption). Requests arriving at the device driver in suspend state are made to wait until operation resumes, after which acceptance processing is performed. If the request does not involve access to the device, however, or otherwise can be processed even during suspension, a request may be accepted without waiting for resumption. TDV RESUME: Resume Device evttyp = TDV RESUME evtinf = NULL (none) Resumption processing takes place as follows. (A) The device power is turned back on, the device states are restored and other device resumption processing is performed. Copyright c○ 2002, 2003 by T-Engine Forum T-Kernel 1.B0.02
5.3. DEVICE MANAGEMENT FUNCTIONS 247 (B) Paused processing is resumed. (C) Request acceptance is resumed. 5.3.8 Special Properties of Disk Devices A disk device has a special role to play in a virtual memory system. In order to realize virtual memory, the OS must call the disk driver for transferring data between memory and disk. The need for the OS to perform data transfer with a disk arises when access is made to nonresident memory and the memory contents must be read from the disk (page in). The OS calls the disk driver in this case. If nonresident memory is accessed in the disk driver, the OS must likewise call the disk driver. In such a case, if the disk driver treats the access to nonresident memory as a wait for page in, it is possible that the OS will again request disk access. Even then, the disk driver must be able to execute the later OS request. A similar case may arise in suspension processing. When access is made to nonresident memory during suspension processing and a disk driver is called, if that disk driver is already suspended, page in will not be possible. To avoid such a situation, suspension processing should suspend other devices before disk devices. If there are multiple disk devices, however, the order of their suspension is indeterminate. For this reason, during suspension processing a disk driver must not access nonresident memory. Because of the above limitations, a disk driver must not use (access) nonresident memory. It is possible, however, that the IO buffer (buf) space designated with tk rea dev or tk wri dev will be nonresident memory, since this is a memory location designated by the caller. In the case of IO buffers, therefore, it is necessary to make the memory space resident (see LockSpace) at the time of IO access. 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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4.9. SYSTEM MANAGEMENT FUNCTIONS 19
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