11.6 Extended Data Space Access [DD]

Qualifying a variable or pointer target as being accessible through the extended data space window allows you to easily access objects that have been placed in a variety of different memory spaces. These include: space(data) (and its subsets), eds, space(eedata), space(prog), space(psv), space(auto_psv), and on some devices space(pmp). Not all devices support all memory spaces.

To use this feature:

• declare an object in an appropriate memory space
• qualify the object with the __eds__ qualifier

For example:

 __eds__ int var_a __attribute__((space(prog)));
 __eds__ int var_b [10] __attribute__((eds));
 __eds__ int *var_c;
 __eds__ int *__eds__ var_d __attribute__((space(psv)));

var_a - declares an int in Flash that is automatically accessed.

var_b - declares an array of ints, located in eds; the elements of the array are automatically accessed.

var_c - declares a pointer to an int, where the destination may exist in any one of the memory spaces supported by Extended Data Space pointers and will be automatically accessed upon dereference; the pointer itself must live in a normal data space.

var_d - declares a pointer to an int, where the destination may exist in any one of the memory spaces supported by Extended Data Space pointers and will be automatically accessed upon dereference; the pointer value exists in Flash and is also automatically accessed.

The compiler will automatically assert the page attribute to scalar variable declarations; this allows the compiler to generate more efficient code when accessing larger data types. Remember, scalar variables do not include structures or arrays. To force paging of a structure or array, please manually use the page attribute and the compiler will prevent the object from crossing a page boundary.

For read access to __eds__ qualified variables, the compiler will automatically manipulate the PSVPAG or DSRPAG register as appropriate. For devices that support extended data space memory, the compiler will also manipulate the DSWPAG register.