Topic       : The GFA-Basic Compendium
Author      : GFA Systemtechnik GmbH
Version     : GFABasic.HYP v2.98 (12/31/2023)
Subject     : Documentation/Programming
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Index Size  : 28056
HCP-Version : 3
Compiled on : Atari
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@hostname   : CAB     
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View Ref-FileCALL addr[(x,y$,...)]

addr: avar (at least 32-bit, ideally integer-type: adr%)
x: iexp
y: sexp

Assembler or C subroutines can also be called with the instruction CALL, where
'addr' is the address of the assembler program, which must end with an RTS
instruction. It is possible to pass a parameter list to the routine.  When the
CALL is made, the return address is found at the top of the stack followed by
the number of parameters given as a 16-bit word, and finally the address, as a
32-bit longword, of the parameter list. All parameters will be put into memory
as long (32-bit) words.

Strings may also be passed to the subroutine, in which case it will be the
address of the string which is found in the parameter list.

Stack structure:

     (sp)  -->  Return address
    4(sp)  -->  Number of parameters (16-bit)
    6(sp)  -->  Address of the parameters (32-bit)

Example: CALL addr%(a&,b&)

To locate the parameters:
    lea 6(sp),a0

     (a0)  -->  a& (4 bytes)
    4(a0)  -->  b& (4 bytes)

Memo: This command is broken in the editor, but works compiled.
      For compiler options see section 'Register Saving'.
      Registers a3 to a7 must remain unchanged.