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3.1.2
Operating Principles of Kernel
A kernel is the core program of real-time OS. The kernel is the software that makes a one-microcomputer system look like
operating a number of microcomputers. You should be wondering how the kernel makes a one-microcomputer system
function like a number of microcomputers.
operating a number of microcomputers. You should be wondering how the kernel makes a one-microcomputer system
function like a number of microcomputers.
As shown in Figure 3.4 the kernel runs a number of tasks according to the time-division system. That is, it changes the task
to execute at fixed time intervals so that a number of tasks appear to be executed simultaneously.
to execute at fixed time intervals so that a number of tasks appear to be executed simultaneously.
Time
Key input
Task
Monitor
Task
Mechanical
control
Task
Volume control
Task
LED
illumination
Task
Remote control
Task
Figure 3.4 Time-division Task Operation
As indicated above, the kernel changes the task to execute at fixed time intervals. This task switching may also be referred
to as dispatching. The factors causing task switching (dispatching) are as follows.
to as dispatching. The factors causing task switching (dispatching) are as follows.
•
Task switching occurs upon request from a task.
•
Task switching occurs due to an external factor such as interrupt.
When a certain task is to be executed again upon task switching, the system resumes its execution at the point of last inter-
ruption (See Figure 3.5).
ruption (See Figure 3.5).