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According to the Hitech manual for v9.80 as Bob says for inline assembler=20
the following is correct.

Excerpt from page 92 of the manual.

unsigned int var;
void main(void)
{
var =3D 1;
#asm // like this...
BCF 0,3
BANKSEL(_var)
RLF (_var)&07fh
RLF (_var+1)&07fh
#endasm

However if the function is written in assembler and called from a C=20
statement, things get a little more complicated.

 From page 89.

The following are guidelines that must be adhered to when writing a routine=
=20
in a
C-callable assembly routine.
? Select, or define, a suitable psect for the executable assembly code
? Select a name (label) for the routine using a leading underscore=20
character
? Ensure that the routine?s label is globally accessible from other modules
? Select an appropriate equivalent C prototype for the routine on which=20
argument
passing can be modelled
? Ensure any symbol used to hold arguments to the routine is globally=20
accessible
? Optionally, use a signature value to enable type checking when the=20
function is
called
? Write the routine ensuring arguments are read from the correct location,=
=20
the return
value is loaded to the correct storage location before returning, if=20
appropriate
? Ensure any local variables required by the routine have space reserved by=
=20
the
appropriate directive
? Use bank selection instructions and mask addresses of symbols
? If the assembly routine calls other C functions or assembly routines,=20
ensure the
compiler is aware of this using the appropriate directives.

Page 91 has, (aspic.h is a Hitech header file for assembly functions).

#include <aspic.h>

GLOBAL _add,?_add ; make _add globally accessible
SIGNAT _add,8298 ; tell the linker how it should be called
FNSIZE _add,0,4 ; this required 4 bytes of params; no autos
; everything following will be placed into the mytext psect
psect mytext,local,class=3DCODE,delta=3D2
; our routine to add to ints and return the result
_add:
; params are loaded by the calling function;
; we access them here using the special symbol
BANKSEL (?_add) ; select the bank of this object
MOVF BANKMASK(?_add+2),w ; take the LSB of the second param
ADDWF BANKMASK(?_add),f ; add to the LSB of the first param
BTFSC STATUS,0 ; check for carry
INCF BANKMASK(?_add+1),f ; handle carry
MOVF BANKMASK(?_add+3),w ; take the MSB of the second param
ADDWF BANKMASK(?_add+1),f ; add to the MSB of the first param
; the result is already in the required location so we can
; just return immediately
RETURN


Colin
--
cdb, colin@btech-online.co.uk on 4/07/2011
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