Forum : ARM
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July 9, 2009 - 7:45pm
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Hi, Version used : - IDE Ride 7.20 Target: - cortex ST103R I have followinf code in my main(): vu16 B; (stacked here) When I debug this code the variable B is never been updated always (0xFFFF) in debug view. When I say never this means with Os, O1 or O2. Most likely this will be OK when having no optimization but that's not the point here. When I change the stack variable in main to have static vu16 B; Its OK When I move the variable to the global variable area it's also OK even without the static keyword. Maybe I have wrong interpretation of the "volatile" but I expected it to be sufficient when using it on some automatic stack variable to skip compiler optimizations. This is apparently not the case ! I didn't checked the assembler output yet but at least I would like to see the value changed in the debug view. Can this be a bug or a bad understanding of me ? Regards |
Hi,
'volatile' means it is possible that the variable changes asynchronously from the function flow, so the function should re-read it every time it reads it, and must 'really write it' every time it writes it. volatile does not force the compiler to place the variable in a place where it can be watched by the debugger. 'static' does, as you saw. In fact, the volatile keyword does not mean anything on a local variable, unless you pass the variable's address to a sub-function. To be 100% sure that you will be able to watch a variable it must be volatile, and also either global, or local and static. (even in O0)
Now, what you describe could still be a problem in Ride (or GCC), but for checking that we will need a complete project (with sources, includes, listings, etc.) that shows the problem. Maybe you should take a look at the assembler and if that doesn't answer your questions, send us a project.
Best Regards,
Vincent