12.3.4 Changing Program Memory Variable Allocation
The variables allocated to program memory can, to some degree, be
allocated to alternate memory locations. Non-Auto Variable Allocation and Access, Changing Non-Auto
Variable Allocation describes alternate addresses and sections also applicable to
objects in the program memory space. Note that you cannot use the
address attribute for objects that are in the
auto_psv space.
The space attribute can be used to define variables
that are positioned for use in the PSV window. To specify certain variables for
allocation in the compiler-managed PSV space, use attribute
space(auto_psv). To allocate variables for PSV access in a section
not managed by the compiler, use attribute space(psv). For more
information on these attributes, see Differences Between MPLAB XC16 and ANSI C.
For example, to place a variable in the auto_psv space,
which will cause storage to be allocated in Flash in a convenient way to be accessed by
a single PSVPAG setting, specify:
unsigned int Flash_variable
__attribute__((space(auto_psv)));
Other user spaces that relate to Flash are available:
space(psv)- a PSV space that the compiler does not access automaticallyspace(prog)- any location in Flash that the compiler does not access automatically
Note that both the psv and auto_psv
spaces are appropriately blocked or aligned so that a single PSVPAG setting is suitable
for accessing the entire variable.
For more on PSV usage, see the MPLAB® XC16 Assembler, Linker and Utilities User’s Guide (DS50002106).