I have just added a bunch of enhancements to the PIC assembler pre-processor
PREPIC.  It is included in the PIC development tools release that can be
downloaded from http://www.embedinc.com/pic/dload.htm.  The updated PREPIC
documentation file can be viewed at
http://www.embedinc.com/pic/prepic.txt.htm.

The major enhancements are the ability to pass arguments to subroutines, and
preprocessor macros that look like native PIC assembler macros.  Unlike
MPASM macros, PREPIC macros can determine whether a particular argument was
passed, and can use these arguments arbitrarily, including building new
symbol names.  Since PREPIC has its own symbols, various computations can be
performed to produce assembler code while guaranteeing not to collide with
assembler symbols.  Since PREPIC runs before the assembler, you can even use
it to "hook" native assembler opcodes and directives.  The PREPIC macro can
emit the expected MPASM code, but also save or look at preprocessor state
and perform other operations.

Just as a example not pretending to be useful, I created a macro for RES and
a new macro SETVAR.  The enhanced RES does the same thing the basic RES
does, but also defines additional pre-processor constants based on the
variable name that indicate the size of the variable and the bank it is in.
SETVAR uses that information to set the variable to a constant value.  Yes,
I know more optimizations are possible.  The point was to demonstrate some
of the new PREPIC capabilities, not to be useful code.

Here is the original source file:

//*********************************************************************
//
// Macro [name] RES, n
//
// Do RES but also create NAME_BANKADR to indicate a address
// in the same bank as the new variable NAME, and NAME_SIZE to
// indicate the variable size in bytes.
//
// The global preprocessor variable BANKADR_CURR contains a address
// within the bank that RES will allocate memory in. If it does not
// exist, then the variable will be assumed to be in unbanked
// memory.
//
/macro res
/write [qstr [arg -1] res [arg 1]]

/if [exist 0 arg] then       ;label was supplied ?
  /var local adr integer = -1 ;init bank adr to indidate unbanked
  /if [exist "bankadr_curr"] then ;bank address supplied ?
    /set adr bankadr_curr    ;use the supplied bank address
    /endif
  /const [arg -1]_bankadr integer = adr
  /endif
/const   [arg    -1]_size integer = [arg 1]
/endmac

//*********************************************************************
//
// Macro SETVAR name, [val]
//
// Set the variable NAME to the value VAL. The default for VAL is 0.
//
/macro setvar
/var local val integer = 0   ;get default value
/if [exist 2 arg] then       ;value was supplied ?
  /set val [arg 2]           ;use the supplied value
  /endif
         dbankif [arg 1]_bankadr ;set bank for access to the variable

/var local byten integer = 0
/var local bval integer      ;value for the current byte
/block
  /set bval [and 255 [shiftr val [* byten 8]]] ;get value for this byte
  /if [= bval 0]
    /then
         clrf    ([arg 1])+[v byten]
    /else
         movlw   [v bval]
         movwf   ([arg 1])+[v byten]
    /endif
  /set byten [+ byten 1]
  /if [< byten [arg 1]_size] then
    /repeat
    /endif
  /endblock
/endmac

//*********************************************************************
//
// Some real code.
//

/var exist bankadr_curr integer = 128 ;set address within this bank
bank1   udata

myvar    res     4           ;my very own variable
junk     res     2           ;trash can

         code

         setvar  myvar, 65538


-------------------------------------------------

Here is the resulting MPASM file produced from the above:

bank1   udata

myvar res 4           ;my very own variable
junk res 2           ;trash can

         code

         dbankif myvar_bankadr ;set bank for access to the variable
         movlw   2
         movwf   (myvar)+0
         clrf    (myvar)+1
         movlw   1
         movwf   (myvar)+2
         clrf    (myvar)+3


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
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