Page 95 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes
accept timer interrupt;

If an aperiodic job is executing, preempt the job;

Current task T = T(t );
k
increment i by 1;

compute the next table entry k = i mod(N);

set the timer to expire at (i/N )*H + t ;
k
if the current task T is i,

let the job at the head of the aperiodic job queue execute;

else, let the task T execute;

sleep;
End Scheduler
Self Assessment

Fill in the blanks:
1. The clock-driven schedulers are those in which the scheduling points are determined by
the ……………… received from a clock.
2. In the event-driven ones, the scheduling points are defined by certain events which
……………… clock interrupts.

3. ……………… scheduling has an ability to consider complex dependencies, communication
delays, and resource contention among jobs when constructing the static schedule,
guaranteeing absence of deadlocks and unpredictable delays .

4. Entire schedule is captured in a ……………… table .
5. Different operating modes can be represented by different ………………
6. Clock-driven approach is appropriate only when the system is ………………, excluding a
few aperiodic and sporadic jobs.

9.3 General Structure of Cyclic Schedules

Figure below shows a good structure of cyclic schedules.

Figure 9.2: Cyclic Frames

Source: ansari.szabist-isb.edu.pk/RTS/RTS0508.ppt

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