ASM

The compiler allows two syntaxes for inline assembler blocks: The ASM block, with { } brackets as for a comment and the standard one without brackets. The syntax of the code inside an assembler block is not verified by the compiler. This is done only by Mad-Assembler during the assembly of the *.a65 output file.

WARNING: The MOS 6502 CPU register X is used to operate the Mad-Pascal software stack. Therefore an assembler block must restore the original value of X at the end of the block, if the register is modified by the block.

ASM
  lda #10
  sta 712
END;

ASM
{  lda #10
   sta 712
};

procedure name; assembler;
asm
  lda #10
  sta 712
end;

procedure name; assembler;
asm
{
  lda #10
  sta 712
};
end;

$LINK

{$link filename}

The compiler directive {$link filename} allows you to link a relocatable object file from Mad-Assembler to a compiled Mad-Pascal program.

    .reloc

.extrn edx .dword

.extrn  print .proc (.dword edx) .var

.public prc


.proc   prc (.dword a .dword b .dword c) .var

.var a,b,c .dword

    print a
    print b
    print c

    rts

.endp

In the above example, we use the PRINT procedure, which is defined in Mad-Pascal.

uses crt;


procedure prc(a,b,c: integer); external;


procedure print(value: dword); keep; register;
begin

 writeln(value);

end;


{$link test.obx}    // link PRC procedure


begin

 prc(11, 347, 321785);

 repeat until keypressed;

end.

From the relocatable object files we have access to Mad-Pascal procedures but only to those marked with the modifier REGISTER, i.e. those whose parameters are passed through the program registers EDX, ECX, EAX (we are limited to a maximum of three parameters).

Mad-Pascal, on the other hand, has access to procedures from the linked assembler file, whose parameters are passed through variables, modifier .VAR.

.proc   prc (.dword a .dword b .dword c) .var

In Mad-Assembler relocatable program, we need an additional declaration of the external symbols EDX, ECX, EAX.

.extrn edx, ecx, eax .dword

The Mad-Pascal procedure itself, which we want to access from the ASM block, is declared as an external procedure with parameters denoting program registers EDX, ECX, EAX.

For more information on the REGISTER modifier and the order in which parameters are allocated in program registers, see Procedures and functions.

.extrn  print .proc (.dword edx) .var

We will access the PRC procedure from the Mad-Pascal level by making it public via the .PUBLIC assembler directive.

.public prc

After assembling our sample relocatable assembler program TEST.ASM, we get the file TEST.OBX, which we can link to the Mad-Pascal program with the {$LINK} directive.

{$link test.obx}