T-Kernel Specification (1.B0.02)

14 CHAPTER 2. CONCEPTS UNDERLYING THE T-KERNEL SPECIFICATION
when tk ret int is executed at the end of the interrupt handler does dispatching occur, causing
Task B to run.
• An extended system call is executed in Task A (priority 8=low), and in its extended SVC handler
(quasi-task portion) tk wup tsk is issued for Task B (priority 2=high). In this case the principle
of delayed dispatching is not applied, so dispatching occurs in tk wup tsk processing. Task A
goes to READY state in a quasi-task portion, and Task B goes to RUN state. Task B is therefore
executed before the rest of the extended SVC handler is completed. The rest of the extended SVC
handler is executed after dispatching occurs again and Task A goes to RUN state.
: Task portion : Task-independent portion
Task A
(low priority)
Task B
(high priority)
Interrupt X
(low priority)
Interrupt Y
(high priority)
Interrupt
✲
Interrupt
nesting
✲
tk wup tsk B
tk wup tsk C
(4) ✛ tk ret int (3)
(2) ✛ tk ret int (1)
• If dispatching does not take place at (1), the remainder of the handler routine for Interrupt X ((2)
to (3)) ends up being put off until later.
Figure 2.7: Interrupt Nesting and Delayed Dispatching
2.6 Objects
“Object” is the general term for resources handled by T-Kernel. Besides tasks, objects include memory
pools, semaphores, event flags, mailboxes and other synchronization and communication mechanisms,
as well as time event handlers (cyclic handlers and alarm handlers).
Attributes can generally be designated when an object is created. Attributes determine detailed differences
in object behavior or the object initial state. When TA XXXXX is designated for an object, that
object is called a “TA XXXXX attribute object”. If there is no particular attribute to be defined, TA NULL
(= 0) is designated. Generally there is no interface provided for reading attributes after an object is
registered.
In an object or handler attribute value, the lower bits indicate system attributes and the upper bits
indicate implementation-dependent attributes. This specification does not define the bit position at
Copyright c○ 2002, 2003 by T-Engine Forum
T-Kernel 1.B0.02