Thursday, 15 June 2017

Insert naughty words about CiderPress here!

Most of tonight was spent banging my head against a press. CiderPress to be specific.

Tonight started well as I managed to discover an Apple II 6502 assembly hello world project that actually used make and CA65/LD65 as the toolchain - exactly what I was after! This was going to be easy...

Building the example was trivial, and that left me with a .BIN file. The makefile, however, used a utility called dos33 to write to the .DSK file which I do not possess, so I simply INIT'd a new disk with a simple HELLO program (I'm becoming quite the DOS 3.3 guru), loaded it into CiderPress, and after selecting the right options imported the .BIN file. Couldn't be simpler, right?

Except I couldn't execute my .BIN file in DOS 3.3 under MAME. Or more specifically, it would crash to the monitor. Hmm...

After the obligatory delete and try again, I researched how to produce .LST and .MAP files, took a quick look at the .BIN file (noticed a 4-byte header), and then tried to locate my program in Apple II memory under MAME. It simply wasn't being loaded at the correct spot, or indeed anywhere I could ascertain.

I initially suspected it was being overwritten by BASIC as soon as it was loaded ($0803); tried changing that to no avail, but then soon decided this track was a red herring after all.

Time to research Apple II DOS 3.3 .BIN file formats. Somewhat frustratingly, it didn't appear within the first few Google hits, or even the next few. I finally found a paragraph detailing the 4-byte prefix in a text file at the bottom of a locked filing cabinet in a disused lavatory with a sign on the door saying "BEWARE OF THE LEOPARD!" My .BIN file looked good so far.

Then I noticed a column heading in the Ciderpress disk viewer called Aux, and wondered what it meant. After taking a little too long to find in the help file, I finally discovered it was supposed to be the execution address of binary files. Mine showed $0000 instead of $0803. Hmm....

Time to grab a random .DSK file from the net and see what CiderPress displays in this column. Apple Panic seemed a good candidate - and each of the several binary files in the image had non-zero addresses. So what was I doing wrong with the import process?

All this had taken a few hours now, and in my desperation - before I succumbed to posting questions on forums - I tried Googling for answers. What I did find was another Apple II hello world tutorial, using what looked like the same source, but this time using CiderPress to transfer the binary to a .DSK file. Bingo!

Let me just say that CiderPress's (seeming) inability to import a standard (adorned) DOS 3.3 .BIN file onto a .DSK image file is, well, simply preposterous! So much so in fact, that I'm not even sure I believe it can't be done! Regardless, as the link infers, I needed to strip off the 4-byte prefix (using dd in my makefile) and then rename the file with the numeric filetype and execution address in the filename. I am speechless. I am without speech.

After all that, I quickly changed a few filenames, modified the example and here we have the very first build of Apple IIGS Asteroids.

My first Apple II program - ever!

Next task is to find a command-line utility that allows me to write my .BIN file to a .DSK image file. There seem to be a few options out there. That's going to be essential as I'll be building this hundreds of times over the next few weeks & months. Right now the biggest bottleneck is waiting for DOS to boot on the Apple II emulation.

Once that's done, I'll need to convert the arcade Asteroids source code to the format that CA65 uses; I'm hoping that won't be too painful as I'll likely have to do it a few times as I finalise the reverse-engineering at a later date.


  1. Upgrade DOS 3.3 to ProntoDOS or DeversiDOS.. Everything loads faster..