As I can see, the keil compiler doesnt use regular stack for functions, and all the local variables inside functions are mapped in global memory. Is there a way, to make it behaive like a normal program should? I.E - create a local variables in ram,and destroy them, when the function ends? Thank you.
Or one function pointer will ruin the whole optimization? Yes ! Because neither the compiler nor the linker will ever be able to unambiguosly figure out which function the pointer will point to at a certain point in the program, and therefore the linker cannot build a calling tree. Please re-read the chapters about memory overlaying and function pointers. Use a switch/case instead. Or, build the calling tree yourself, though that is probably the more complicated solution.
Thank you, Christoph, for your help. Now i know the problem, i will try to handle it. Thank you again.
As a matter of fact,here lies the solution http://www.keil.com/support/man/docs/bl51/bl51_ol_fp.htm I will try this. Thanx again :)
" ... one function pointer will ruin the whole optimization ... Because neither the compiler nor the linker will ever be able to unambiguosly figure out which function the pointer will point to at a certain point in the program, and therefore the linker cannot build a calling tree." Not necessarily. There is an Application Note that describes the necessary steps for safe use of function pointers in C51: http://www.keil.com/appnotes/docs/apnt_129.asp Also, search the knowledgebas for "function pointer"
Not necessarily. Quite necessarily. The Appnote mentions that. The linker cannot figure out the calling tree on its own, it has to be told (through directives) what the calling relations are. Still ... function pointers are messy. They make the program very difficult to understand for anyone trying to maintain the program. They cause even more issues on a '51. Only use them if they are the only way to do what you're trying to do. (and I doubt the latter applies to a lot of things).
The Application Note describes a way to use tables of function pointers without having to resort to manual OVERLAY directives: "The C51 Compiler and BL51 Linker work in combination to make overlaying the variable space of function easy when you use tables of function pointers. However, you must declare the pointer tables appropriately. If you do this, you can avoid using the OVERLAY directive." (my emphasis). Typically, function pointers used to implement a state machine would be used in tables. "Still ... function pointers are messy. They make the program very difficult to understand for anyone trying to maintain the program." I disagree. A large state machine implemented with switch states can be very cumbersome to maintain; function pointers can be very beneficial here! Whether that makes them a good idea on an 8051, though, remains open to question...