A 68000 macro assembler that takes the place of asm68k, the assembler of the SN Systems / Psy-Q development system. It reads the same source, takes the same command line and produces the same output, and it runs anywhere Rust does.

Output is compared byte for byte with that of asm68k 2.53, for object code and listings alike. See Testing.

cargo build --release

The program is target/release/slop68k. It depends on nothing but the Rust standard library.

There are two ways of writing the command line, which can be mixed.

slop68k /k /p /o ae- source,object,symbols,listing

This is the command line of asm68k, so in a build script written for it, it is enough to change the name of the program. File names may use backslashes, and are found whatever their case, as sources written on Windows expect.

slop68k -I include -D DEBUG=1 -O ae-,c+ -o build/main.o src/main.68k

Options may come before or after the source, and a value may be attached to its option, as in -Iinclude and --output=main.o. Without -f, /p, /ps or /l the name of the output decides its format: ELF for .o, S-records for .s19, .s28, .s37 and .srec, and binary for anything else. Without an output file the source is assembled and nothing written.

Messages go to standard output, in the format of asm68k:

src/main.68k(12) : Error : Illegal addressing mode
	move.b	d0,a0

The exit status is zero if there were no errors.

_year, _month and the other date and time constants are taken from the clock, in UTC. With --local-time they are in local time, as they are with asm68k. This is there on Linux only; elsewhere it gives a warning and UTC.

For builds that have to come out the same every time, set SOURCE_DATE_EPOCH to the time to use, in seconds since 1970.

Object files are in the ELF format, for the GNU linker, to be linked with code from GCC. In a makefile:

%.o: %.68k
	slop68k -q -O c+ -I include -o $@ $<

• Each SECTION becomes a section of the object file. Code that is not in a section goes in .text. Name sections .text, .data, .rodata and .bss to have them treated as the compiler's are.
• XDEF, GLOBAL and PUBLIC make symbols global; XREF and GLOBAL declare those defined elsewhere. A symbol that is neither defined nor declared is an error, as it is with asm68k.
• ORG cannot be used.
• Names are not case sensitive unless c+ is among the options. They are written to the object file as they are spelled where they are defined or declared.
• GCC for m68k-elf does not put an underscore in front of the names of C, so a function is called by its name: jsr main.
• Code is for the 68000, so C is to be compiled with -m68000.

docs/compatibility.md describes the behaviour of asm68k that this assembler reproduces, much of which is not in the manual, and the ways in which the two differ. The main differences:

• Without /p, asm68k writes an executable in its own CPE format. Here the default is a binary file.
• /l writes ELF rather than Psy-Q link files.
• Options that start with a dash are an addition.
• The order of symbols in the symbol file differs.
• Downloading to a target machine is not there.

cargo test

The cases in tests/cases are assembled and the object code, listing and messages compared with those of asm68k, which are kept alongside them. To make them anew, with Wine and a copy of asm68k.exe:

ASM68K=/path/to/asm68k.exe tests/regen.sh

If there is a GCC toolchain for m68k-elf, programs written for this assembler and for the GNU assembler are linked with C code, and the results compared. The toolchain is looked for in the PATH and in /opt/toolchains/m68k-elf/bin; set M68K_ELF to the prefix of its programs (such as /usr/local/bin/m68k-elf-) if it is somewhere else. Without a toolchain these tests do nothing.

Beyond these the assembler has been checked against asm68k with several complete programs, among them the Sonic the Hedgehog disassembly in its version for asm68k: 153,000 lines that assemble to the same 512 KB.

This is free to use for any purpose, under the terms of either the BSD Zero Clause License or the Unlicense, as you prefer.