[IsaMc68k] Prototype an assembler suite

[sporniket]

Incubation in progress : https://github.com/sporniket/python-sandbox/tree/main/py-isa-m68k

Step 1 -- Compile and generate a minimal program for Atari ST

The smallest valid program (*.PRG file) is a call to the GEMDOS function Pterm0

                move.w  #0,-(sp) ; Offset 0
                trap    #1      ; GEMDOS

Save this program in to a file named justquit.s.

TO BE DEFINED -- command line interface

• name : tentatively m68k_as
• output format : target-format/F ; ~check the manual of GNU AS to see how the "format" of the output is specified~.
  • --target-format bin = just the compiled instruction, no header or other things like relocation table ; **this is the default format
  • --target-format tos = generate an executable program for the Atari ST Operating System (TOS) ; if executable supporting parameters (*.TTP extension, as Tos Takes Parameters) is different, there will be a tos-ttp format.
  • --target-format elf generates an ELF program
• output file name : output, by default, a.out

Step 1.a -- compile the two lines of code

When invoking m68k_as justquit.s

Then the resulting a.out MUST be the same as compiling the program with vasm with the command : vasmm68k_mot -Fbin justquit.s.

0b0011.111.100.111.100 0b0000.0000.0000.0000    $3F3C $0000     ; move #0,-(sp) 
0b0100.111.001.000.001                          $4E41           ; trap #1

This step requires :

• parsing each line :
  • breaking down into labels, mnemonic, operands, comment
  • mnemonic : recognize move with a size suffix .m, and trap
  • operands : break down into list of operands, recognize litteral value #<number>, predecrement address mode, and alternate name sp for a7
• for each line of code, generate a byte stream + metadata
• gather all byte stream into the final file

Step 1.b -- generate an executable program

See The program format.

When invoking m68k_as --output justquit.prg --target-format tos justquit.s

Then the resulting file justquit.prg MUST be the same as compiling the program with vasm with the command : vasmm68k_mot -Ftos -o justquit.tos justquit.s