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My software doesn't work if optimization is enabled

100prathima

Hi:
I am currently working on an embedded software with hard real time constraints. My ISR should execute every milli second. I have a working software version(standalone) which I need to optimize. If I simply enable -o2 or -o3, the software doesn't work as before. So, how do I use these optimization options in a real time system? Am I missing anything? 

  • 0

    Software optimization using compiler settings is usually pretty safe, but if you are using code such as that typically found in an ISR, you may have variables that are changed outside the current execution context.  Since the compiler may not be aware of this, optimizing the code can result in removal of "extraneous" variables (which are actually critical) or the reordering of code to "optimize" pipeline operations (which in some cases inadvertently changes a critical flow sequence) causing an incorrect result.

    So in the vast majority of cases you can solve the problem by using #pragmas to control the level of GCC optimization, or declaring variables as volatile so the compiler doesn't optimize them out when it shouldn't.

    Ron

  • 0 in reply to Former Member

    I was enabling the project optimization and it was not working. If I select optimization for required files, the code works and there seems to be improvement. So, what is the difference between file level optimization and optimization for entire project?