11.3.4.1 Managed PSV Access [DD]

Note: The features described in this section are not required for dsPIC33A devices. In most cases the features will be silently ignored. For more detail, refer to Compiler-Specific Type Qualifiers.

The compiler introduces several new qualifiers (or more specifically, CV-qualifiers). Like a const volatile qualifier, the new qualifiers can be applied to objects or pointer targets. These qualifiers are:

  • __psv__ for accessing objects that do not cross a PSV boundary, such as those allocated in space(auto_psv) or space(psv).
  • __prog__ for accessing objects that may cross a PSV boundary, specifically those allocated in space(prog), but it may be applied to any object in Flash.
  • __eds__ for accessing objects that may be in Flash or the extended data space (for devices with > 32K of RAM), see __eds__ in Extended Data Space Access [DD].

Typically there is no need to specify __psv__ or __prog__ for an object placed in space(auto_psv).

Defining a variable in a compiler managed Flash space is accomplished by:

__psv__ unsigned int Flash_variable __attribute__((space(psv)));

Reading from the variable now will cause the compiler to generate code that adjusts the appropriate PSV page SFR as necessary to access the variable correctly. These qualifiers can equally decorate pointers:

__psv__ unsigned int *pFlash;

produces a pointer to something in PSV, which can be assigned to a managed PSV object in the normal way. For example:

pFlash = &Flash_variable;