JAVA-BASED REAL-TIME PROGRAMMING
JAVA-BASED REAL-TIME PROGRAMMING
JAVA-BASED REAL-TIME PROGRAMMING
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4.2 Exercise 2 – Lab 1 preparation<br />
4.2. Exercise 2 – Lab 1 preparation<br />
In this exercise you will design a real-time system for an alarm clock application<br />
using threads, semaphores and provided hardware interfaces. In lab 1<br />
you will implement your design (the implementation usually takes longer than<br />
two hours so be sure to start well in advance of the lab occasion). Study the<br />
provided specification, description of the handout code and hardware emulator<br />
and answer the following questions (express your design in class diagrams<br />
and Java code where necessary):<br />
1. What parallel activities are needed, i.e., which thread objects do you<br />
need?<br />
2. What common data need to be shared between threads? Where is the<br />
data to be stored?<br />
3. What operations on data are needed for each thread? Where should this<br />
logic be stored?<br />
4. Where will data be accessed concurrently from different threads, i.e.<br />
where do you need to provide mutual exclusion?<br />
5. Are there other situations in the alarm clock where semaphores are<br />
needed for synchronization?<br />
Hint: study the ClockInput class.<br />
6. If you in a thread wait for the next second by simply calling sleep(1000),<br />
what will the effect on the clock time be? Is this ok for alarm clock time<br />
updating? Can it be improved?<br />
Specification<br />
1. The displayed clock time should be updated every second (by calling<br />
the ClockOutput.showTime method). Note: when the user has selected<br />
set alarm or set time, the hardware/emulator shows the set time and an<br />
update of the clock time will have no effect on the clock display. Still,<br />
the clock time should be updated every second regardless of mode.<br />
2. It should be possible to set the clock time and the alarm time. The hardware/emulator<br />
internally handles the actual setting/editing of the time<br />
value. When the user selects another mode, the set value is written to<br />
the ClockInput object and give is called for its semaphore. For example,<br />
the user selects set alarm and edits (using number keys or arrows) the<br />
alarm time. Nothing needs to be done by the control software. Then<br />
the user selects set time and the alarm time is written to the ClockInput<br />
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