ASM

Assembler blocks are not verified for syntax by the compiler, this is done only by Mad Assembler.

WARNING:
It is required to maintain the state of the X CPU6502 register, which is used to operate the MP software stack.

The compiler allows two syntaxes for the ASM block, with { } brackets as for a comment and the standard one without brackets.

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 attach a relocatable file from Mad Assembler to a compiled MP 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 MP.

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 assembler level we have access to MP procedures but only 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).

The KEEP modifier forces a procedure to remain in the compiled code regardless of whether its use has occurred or not (normally procedures/functions that are not used are eliminated).

MP, 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 MP procedure itself, which we want to access from the assembler level, 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 MP 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 MP program with the {$LINK} directive.

{$link test.obx}