Mpc5634 reference manual

It was based on a task structure — each task representing a virtual CPU. Tasks can be in one of three states:. If the event has already occurred , the call returns immediately after setting the ECW to 0. When an event occurs, POST is called, which tests whether a task is waiting or not. Otherwise, a task is waiting. When the task just posted becomes active, it will start executing just after the WAIT call which caused the task to be suspended. One for events in a task and the other for events generated in an interrupt handler.

The actual interrupt handlers and drivers in OSCAR also deal with the high-speed paper tape reader and punch in a nearly identical way. Other devices could be added very easily. That book describes this facility as follows:.

Event synchronization is the delaying of task execution until some specified event occurs. The synchronization has two aspects. The notification required is performed by the POST routine.

When the event is known to the control program for example the completion of a read operation , the control program issues the POST. Genuys, , p. Semaphores are essentially non-negative integers. These are called binary semaphores. There are many applications for semaphores with larger values, which are known as general semaphores.

The zero or positive count of a general semaphore may be used as a counter for recording the amount of a resource controlled by it — e. The small application TEST8. The lines are each printed in a mutually exclusive section guarded by a common semaphore. This means that if two different characters are typed before a line has finished printing, the printing is blocked until one line has been completely printed.

A feature of this application is, that the program for the 3 printing tasks is the same — it is re-entrant. This demo worked well with a slow teleprinter. The SIMH emulation output is so fast, that it is hard to enter a second character before a character line has been output. One way to do it is to type a sequence e.

The output will be:. The need for such a debugger in the control environment was very important because conventional debuggers do not work well in an environment with interrupts. It uses the Teletype for input and output. These follow the standard pattern of Nova Debug programs. A sequence of memory locations may be searched for a particular word after it is masked.

This operation also allows the listing of a sequence of memory locations. A Breakpoint may be entered at any memory location. Because of the logical processor concept of tasks this scheme makes debugging of real-time systems very tractable. The inspection of variables, while a system is running, is particularly useful. This is important when a system is controlling a factory process. It is then undesirable to stop the system. The following is a case study of a typical debugging session.

By observation of the behaviour of certain variables and by inspection of the program listing it was determined that a control algorithm was faulty. This became evident because one control loop in a system containing a number of control loops was unstable.

The system was running online and the unstable behaviour was not severe enough to warrant a shutdown. A modification to the control algorithm program was written and checked on paper to make reasonably sure that it would work.

Then the modification was entered into a spare section of the computer memory as a patch. The whole patch was typed in and checked while the rest of the system operated with the old algorithm. Then a statement in the control algorithm was overwritten with a branch instruction to the patch. The next execution of that algorithm then executed the patch. The effect of the patch may then be observed. If the action of the patch makes the system worse the branch instruction is again overwritten with the old instruction.

This restores the old algorithm. If the patch causes wild operation then the system will of course crash. But this kind of modification was carried out repeatedly on an online system and very few mistakes were made. The final operation, if a patch is successful, is to list it and also to punch out a binary tape of the patch. This may again be done while the rest of the system is online. The time involved in planning and coding the first version of OSCAR took 4 months during the latter part of During the next 2 years, a number of modifications to the system were made.

In particular Semaphores and Double-Ended Queues were added. Experience with the system has shown that it is easily picked up by programmers.

The functions, particularly the synchronising primitives, are at first unfamiliar but with a little practice, they are used as intended. Thus parallel programming as against uni-programming comes naturally to most programmers when a task structured system such as OSCAR is available to them. There is still a certain amount of resistance to going all the way with the parallel approach. Embedded Software Embedded Software from Partners 9. All resource types Minify.

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