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SBASIC Manual - Page 55

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     SBasic User's Manual     SBasic Version 2.7             Page 55
     Printed:  December 5, 1999
     The ASMFUNC statement

     The ASMFUNC statement gives SB access to labels and routines within a
     block of assembly language code.  See the section above on the ASM
     statement.  The format for the ASMFUNC statement is:

         asmfunc  foo

     This statement tells the SBasic compiler that subsequent references to
     the label FOO must be passed to the output file as FOO, not as a
     converted label.

     ASMFUNC adds tremendous power to SB, allowing you to write your own
     SBasic extensions in assembly language, then use them as if they were
     an integral part of SB.  For example:

         declare  stack                 ' declare a variable
         asmfunc  getstk                ' define an asm entry point

         main:                          ' enter here
         stack = getstk(0)              ' get addr of return stack
         do  loop                       ' silly loop

         asm                            ' switch to assembly language
         getstk                         ' entry point to getstk()
             tsx                        ' move addr of stack to x
             xgdx                       ' move addr of stack to d
             rts                        ' return addr of stack
         endasm                         ' back to SBasic


     Here, the ASMFUNC statement tells SB that references to the label
     GETSTK are to be passed unchanged to the output file.  Thus, when the
     SB code invokes the function GETSTK() to get the current hardware
     stack address, SB generates a JSR to GETSTK, not a JSR to an address
     with an internal SB label.

     The actual code for subroutine GETSTK exists in the ASM block.  GETSTK
     moves the stack pointer into the 68hc11's D-register and returns.  The
     code generated by SB then stores the D-register into variable STACK
     and falls into the silly loop at the end of the program.

     This example shows how to set up an ASMFUNC statement and its
     associated assembly language.  It also shows how to use an ASMFUNC
     label as a function.  In this case, you must adhere to SBasic's
     general rules regarding functions.  Functions, which return a result
     in the D-register, must be called with an argument.  Since the GETSTK
     routine doesn't need an argument, anything will work, but you must
     include an argument of some kind.  That's why I show an argument of 0
     for GETSTK.