> In cases like that, you can do your caching manually. Just read the rom > value once, and keep the value in a local variable - then it will stay > in a local register. If you have a lot to read and re-use, copy a block> to SRAM. This is something that the compiler could never do on its own > you have to write it in the code. Yes, this is obvious, but in some cases this is not feasible, such as porting a large codebase to a new platform with time constraints and/or porting code where the license prohibits changing the code. > This was already explained to you by Florian - the compiler cannot make > the optimisation you want, because it does not know that the object at > address 0x1234 is truly constant. The "const" in the pointer here can > only tell the compiler that /you/ will not try to change its value. > This is different from the case where you define pfoo from the address > of foo, because you have defined foo to be constant - now the compiler > knows it cannot change, and can optimise accordingly. > be able to get the kind of optimisation you are asking for, you would > need to be able to tell the compiler that the thing pfoo points to is > really constant - that would need a new __attribute__ or similar > extension. Alternatively, you would need a new __attribute__ to let you > declare a const foo at a specific address (this might be easier, since > the relevant __attribute__ already exists for avr-gcc). The --defsyms approach seems easier. Toshi
