Introduction to C64 crossdevelopment by Cadaver

Welcome to the very first rant at, about
crossdeveloping for the C64 and the methods I personally use (not
necessarily most recommended)

0. Background

Some of the opinions in this rant are quite radical. To have some background
to them I'll first give my short C64 history:

- 1986 Got hands on a C64
- 1987 BASIC experiments
- 1988-1991 Assembly language experiments. Not much achieved, all bigger
projects are unfinished. (part of it can be blamed on primitive tools:
SEUCK and MikroAssembler)
- 1992- Mostly only playing on C64 from this point onwards
- 1995 Discovered C64 emulation
- 1996 or 1997 C64 stops working
- 1998 Got idea of crossdevelopment by researching the internet; work
  on Metal Warrior game started; unforeseen levels of C64 productivity
- 1999-2000 Crossdevelopment, crossdevelopment, crossdevelopment
- 2001- Acquired working C64 hardware again, crossdevelopment continues...

So, basically I have crossdevelopment to thank for all my C64 achievements
worth mentioning.

1. What is crossdevelopment

Crossdevelopment is using a different (usually, more powerful) platform than
the target platform for running some or all of the programs used in
development. (assembler, text editor, possibly graphics/music editor)

Advantages of C64 crossdevelopment:

- Shorter compile times because of CPU power

- Batch files or makefiles can automatize compiling process

- Editing can be easier or faster on modern utilities (for example a PC
  based text editor for writing source code)

- Files on a harddisk are easier to manage, as well as more reliably
  stored than on floppy disk (though, some people have harddisk-equipped
  C64s.) In any case, remember the importance of backups!

Disadvantages of C64 crossdevelopment:

- If testing on an emulator, remember that graphics (TV image blurriness!) &
  sound emulation are not 100% accurate yet, and probably will never be.
  Processor- & chip-emulation are very accurate nowadays in good emulators (for
  example CCS64, VICE). If your program runs in both CCS64 & VICE you can
  be 99% sure that it will also on real C64.

  Be careful with custom disk-routines! (fastloaders etc.) If using emulators,
  test them under both VICE (using several emulated drive-models) & CCS64
  to be 99% sure it works. To be 100% sure, test on real C64. I have
  firsthand experience of an unknown drivecode-related bug that appeared
  on CCS64 & real C64 but not on VICE.

- If testing on a real C64, some effort is required to transfer the
  program over (for example, with Star Commander and an X1541 cable). But
  I strongly recommend testing on real C64, whenever possible!

- Making small test changes to code & data (for example with a freezer
  cartridge) during run-time can be more convenient than recompiling the
  project within the crossdevelopment-system.

Crossdevelopment can also be "mixed": for example a C64 emulator is run to
use C64 based graphics & music editors. The resulting datafiles are then
extracted from a D64 disk-image as needed (VICE has also the possibility to
"mount" a hard disk directory directly; no need for disk images)

2. My principles and tools

My crossdevelopment principle is very extreme but it is the most efficient
for me personally. Simply put, it is:

- No C64-based utilities are used in development

At first glance this seems extremely crazy, when one is developing a C64
program it would seem logical to use the tried & true utilities, at least for
some tasks. Here follows my personal solutions for each front: (not always
obeying the rule 100%)

2.1 The source code

I use TSE (DOS based editor, great keyboard commands) to edit the source code,
splitting source code to multiple files based on their purposes (for example
all raster interrupt code goes to one file, all scrolling code goes to another) 
to keep things manageable.

Also, with the memory not being a concern like in C64 based combined editor/
assemblers (Turboassembler for example) I can comment as much as I want and
use as long label names as needed.

Recently I've also been experimenting with the Windows-based ConTEXT editor.

2.2 Background and sprite graphics

Drawing sprites is usually a generic task, it is quite the same from project to
project. Therefore a C64 based sprite editor would usually fit the task just
fine, without need for any customizations (for example the SEUCK sprite editor)

However, in background graphics problems quickly arise. SEUCK would be fine
for simple scrolling games, but

- It is limited to vertical-scrolling backgrounds only

- Blocks are 5x5 chars. What if you want 4x4?

So, it is likely that a custom utility is needed. I have no doubt that I will
write an editor for a 32-bit platform in C language faster than I could write a
C64 based editor in assembly language (and an editor written in BASIC would be
intolerably slow for any larger amounts of work, in most cases) This, like
everything, is a matter of preference. For others it can be faster to write a
C64 based utility, even in assembly language.

And once I got my first background editor finished, the common routines and
graphics were also convenient to use for a PC-based sprite editor as well.

If you're interested in coding graphics editors on a 32-bit platform, I
suggest using the portable SDL library or perhaps my own BME library,
that uses SDL but has some higher-level functionality such as sprites
already implemented.

2.3 Bitmap pictures

I got used to Deluxe Paint during my Amiga programming years. Therefore,
painting in a Deluxe Paint-style program (nowadays I use GRAFX2 for better
NT/W2K compatibility) feels most natural to me. So, I set up a C64-like
palette, a 2x1 grid and brush size and begin painting.

(GRAFX2 is available at

The problem is this: C64 can have only three different colors + background
color in a character cell. But how I know if I exceed this limit in a non-C64
paint program? There is no way, except by examining the pixels by eye, or
testing the picture within a C64 program.

Although work by this method is fast for me even with all testing
involved, it is not fully satisfying. A PC-based C64 paint program would
be ideal, but a paint program is a much bigger task than a background
char-set editor: I'm quite sure I won't write one. I'm also afraid of the flood
of feature-requests...

For the conversion of IFF/LBM pictures to C64 usable format, I use simple,
self-written utilities.

I know this method is a bit weird and therefore I'd rather recommend using a
C64 bitmap paint program. However, it's worth trying once in a lifetime!

2.4 Music and sound

Like in the previous chapter, the method I'd recommend most is a C64 based
editor (mainly because there are so many available) But now let's examine
what I wanted...

To have maximum control over my programs, I've always preferred using a self-
written playroutine. Not many playroutines offer sound effect support anyway,
and many playroutines (with lots of features, but not geared for game use) are
kind of slow.

So far, I've used 3 options:

- Editing music directly in source code as byte data. Symbolic defines can help
  this process (for example note names) but still I can't really recommend
  this method to anyone working today. This is useful if one has to squeeze
  every last byte out of the music data.

  For example in Metal Warrior 3 memory was extremely tight, so I programmed a
  "subroutine call" system in the music sequence data. Thus the music data
  became almost like program code, and possibly source-code editing was
  even the most efficient way this time.

- Writing a C64 based editor. I did this with SadoTracker, and again with
  NinjaTracker. Extracting the ready tunes from diskimages was a pain, though
  (I automated it later)

- GoatTracker. A PC based C64 music editor supporting either reSID emulation
  or the HardSid.

2.5 Assembling

My crossassembler of choice is DASM by Matthew Dillon, but there's a lot of
good crossassemblers to choose from. Some features I require from an assembler,
not much really:

- Able to handle big files (practically, the assembler must have been
compiled with a 32bit C compiler)

- Macro and repeat statement support

- Code generation to different logical vs. physical address; for example code
  executed in the disk drive or depacker code to be copied into another
  memory location

- Possibility to include other source code files and raw binary data

So basically the "main program" source code file for my productions looks like

        processor 6502 ;DASM supports multiple processors
        org startaddress

        ..main program code here..

        include other_sourcecodefile_1.s
        include other_sourcecodefile_2.s
        include other_sourcecodefile_n.s

        incbin some_data.bin
        incbin some_more_data.bin

And the whole program is assembled by giving an instruction like

        dasm program.s -oprogram.prg -p3

(-p3 enables 3 passes for assembly)

2.6 Controlling the compile process

A complex production might be composed of many files that are for example
loaded from disk as needed. So it would be clumsy to have to type all
assembling & data-manipulation commands by hand each time something needs to
be changed.

A batch file will do fine in most cases; simply gather all commands required
to fully compile the program.

But through C programming I've learned a more elegant solution: the use of a
makefile. A makefile lists the dependencies for all target files and the
commands needed to create them. The makefile can then executed by a C
compiler's make utility, and a file is re-created only if some of the files
it's depending on is changed (saves time). Here's an example of a makefile,
showing a main program which depends on some source code files and a picture
file: (using a fictional picture convert utility)

program.prg: picture.raw program.s raster.s screen.s
        dasm program.s -oprogram.prg

picture.raw: picture.iff
        convert picture.iff picture.raw

2.7 Cross-compression

Don't want to wait minutes or hours for a C64-based packer or cruncher to
finish? I have a simple advice, use Pucrunch by Pasi 'Albert' Ojala or
Exomizer by Magnus Lind. They can also be integrated into a loadersystem quite
easily. Exomizer is more efficient and has smaller decompression routine,
but compression takes a lot of time.

Pucrunch homepage
Exomizer homepage

2.8 Building a diskimage for testing

Now there's a bunch of files sitting on the harddisk that are ready for
execution/loading on the C64. If there's only one file, the executable, the
next step is unnecessary; the file can be transferred onto a C64 floppy,
directly to the C64 with the PC64 cable, or run in an emulator.
Also, if testing happens exclusively on a real C64, a multi-part program
can be transferred one file at a time onto a C64 floppy.

But still it's good to know how to build a diskimage. Some methods are:

- Using a program such as Star Commander or 64Copy to create a new D64 image
  and copy the files to it. As far as I know, this has to be done manually
  (not very convenient.)

- Using the C1541 program included with the VICE emulator. It includes commands
  to create & format a new diskimage and copy files onto it. By feeding a
  command file to the program a diskimage can be built automatically.

- Using some other utility to copy files to a diskimage one by one. Personally
  I use a self-written program called MAKEDISK that takes a list file of all
  files to be copied and creates a diskimage from scratch (disk name and
  sector interleave can be given as command line parameters.)

3. Conclusion

This rant has reached its end and all major aspects of crossdevelopment
have probably been addressed. Remember, all custom utilities mentioned in
this text are available at the tools section at

Good luck in C64 development!

                                                  Lasse Öörni