4.1 Access_ovr Directive

Suggested Replacement

Define a psect with the ovrld flag set. Associate the psect with the Access bank linker class, COMRAM to have it linked somewhere in the PIC18's Access Bank.

The example following shows objects placed into the myData psect, which is used in two different modules (file 1 and file 2). The PSECT directive uses the same psect name, ovrld flag (to indicate that the psects will be overlaid), and space=1 flag (to indicate the psects will reside in the data space memory). The psects are associated with the PIC18 COMRAM linker class, which defines the Access Bank memory, so once overlaid, myData will appear anywhere in the memory defined by this class.

;file 1
PSECT myData,space=1,ovrld,class=COMRAM
zero:
  DS 1
  ;leave a 1-byte gap for another object here
  ORG 2
two:
  DS 1

;file 2
PSECT myData,space=1,ovrld,class=COMRAM
  ORG 1
one:
  DS 1

Note that the contributions to an overlaid psect are concatenated in each module, but the psects from each module are then overlaid at link time. When the above example is built, the labels will appear in memory in the order zero, one, two.

The ORG directive in the above example has allowed the psects' content to interleave. If this directive had not been used in file 1, the space associated with the label zero and the label one would overlap, and these objects would appear at the same address. Such code is legal and may be desired in some applications.

Overlaid psects can be linked into any RAM area, not just the Access bank, and this construct will work on any device with the selection of a suitable linker class.