I just found out the hard way that the new version of ASM30 has an important
incompatibility to older versions.  I just upgraded MPLAB to 7.11 from some
older release of version 7.  I used to be able to do IFDEF on SFR symbols to
automatically configure code to the particular processor.  However, these
IFDEFs now always indicate the symbol is not defined.

After some rummaging around, I think this has to do with different treatment
of external symbols.  Previously an external symbol would be "defined" as
reported by IFDEF, but is not in the new version.  In other words the
following snippet of code would act differently on old and new versions of
ASM30:

extern xxx
ifdef xxx
    .print "xxx defined"
  .else
    .pring "xxx undefined"
  .endif

This really messes up my code, and I'm trying to figure out how to address
this problem.  I haven't heard back from Microchip whether this is a bug or
an intentional change.  If the latter, it's going to take some work to get
around.  The only robust method I can think of is to write code that
interprets the linker file, extracts definitions of symbols to fixed
addresses, and automatically creates an include file containing those
symbols for each processor.  Writing the general parser for the complete
linker file syntax will take a day or two, and a simple parser will be
vulnerable to legitimate changes to linker file structure.  Yuck.


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