Start
• Task
Function •
Scheduling
and Timeslice •
Task
Context •
Task
Control Block •
Global
Variables •
Memory
Management •
API
•
Assembly
Functions •
Give
it a Try •
Enhancements
•
References,
Sources & PDF
TASK
CONTROL BLOCK
The data structure TaskControlBlock
(see Listing 3) describes a task. µexec keeps all tasks in
a circular linked list and a global variable keeps
track of the current task.
To choose the next task
to run, µexec follows the next pointer field of the
current task and sets the current-task variable accordingly.
To ensure that there is always at least one task to
run, the system creates a null task. It calls UEXC_Defer
in an infinite loop, enabling other tasks to run.
If no other task is there, the system runs this null
task indefinitely.
A task is identified
by its task ID, which is kept in the tid field. ticks
is the number of ticks that the task should execute
before scheduling occurs (i.e., its timeslice value).
current_ ticks is the number of ticks left in the
execution of this task.
func is the pointer to
the C function for the task. The stack start and end
values are for debugging purposes, such as detecting
stack overrun. sp is the current value of the stack
pointer. It must be within the range of the start
and end stack values.
