General question: Adding new test code to embedded system

this maybe will be off topic, but I am preparing for an exam in real time. And I have been browsing the book a开发者_运维技巧nd Internet for an answer for a problem.

Basically I wonder if by adding additional test code if it may change the real time behavior for an embedded system, and or also if it will introduce new errors.

Anyone who might know the answer for this, or refer me to some reading material for it?

Your question is too general.. So I guess the default answer would be it depends.. But considering the possibilities as an exercise of logic and thought, yes it surely can!

There are many schemes available to guarantee the 'real-timeness' of an embedded system. For example, one can have a pre-emptive timer based ISR to service the real-time task.. In such a case, your test code could possibly not affect the 'real-timeness'.. But if the testing takes too long, and the context switches are not pre-emptive, you could get into trouble..

But again it depends on what you're testing and how you're testing. Your test code can possible mess with the timers, interrupts or the memory of system. The possibilities to mess up stuff if you're not careful are endless..

Having an OS underneath will prevent some errors, but again depending on how it works, you may be saved from bad 'test code'..

Yes, when you add code (test, diagnostic, statistic) it may change the real time behavior. It depends on the design, the implementation and the CPU power if it will actually change the behavior. You also have more lines of code and the probability for errors may increase. But I wouldn't say, "it will introduce errors", since it can introduce errors.

Yes it can. See How can adding data to a segment in flash memory screw up a program's timing? for an example of how even adding non-executable code can adjust timing enough to screw up a system.

Yea, changing your code base could totally change its timing. Consider if you dumped some debug output to a serial port, it takes time to call that function, format the data, and if the function is synchronous, then for it to wait for data to go out. This kinda stuff definitely changes system timing behavior.