the PIC or 8051), some compilers will use a const qualifier to signal that they should place the variables into the code store and use different instructions to access them, while others will not. On processors where the code store is in a different address space (e.g. This will reduce the amount of RAM required by the program, and will reduce the amount of work the startup code has to do. On processors where the code store is in the same address space as all other variables, compilers will typically place "const"-qualified global or static variables into their own link section, and linkers will typically be configured to place that section in the system's code store (flash, OTP, or whatever). This solves also your confusion about flash-less systems. Global variables are stored in RAM, just like mentioned before. And these steps do not execute in a single cycle like a simple store into RAM does. Think about it: To write a single bit of flash, you have to erase a whole block of data an then rewrite the whole thing with the modified data. The scope of a certain variable matters only to the compiler, at the machine code level nobody prevents you from reading a local variable outside of a function (as long as your controller doesn't have some fancy features to protect memory areas from being accessed).Īnd global variables are stored in Flash. Static variables are stored in RAM, just like your global variables. Static vars are definitely not stored on the heap, since this is only for variables allocated during run time (and static vars are allocated during compile time). The following answer is based on my experience looking at mapfiles, if I'm wrong about sth.
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