This is a small sample application which targets mainly an ancient machine, the Sinclair QL, but it can be also compiled for and played on any Unix terminal with ncurses capability. Since the QL was my first 'professional' computer I was interested to find out how it compares to modern hardware and how it feels to develop and compile software on it in the 21st century.
The QL was announced to the public in 1983 a few weeks before the Apple Macintosh. In this time the machine was quite interesting. Based on a Motorola 68008 it provided an internal 32bit CPU architecture, high resolution graphics, two microdrive units with a storage capacity of 100 Kilobytes each and an office software bundle including text processing, spreadsheet, business graphics and database. On contrast to the Macintosh and the IBM PC the QL was with an initial price of less then £400 in the UK very affordable. Nevertheless the machine failed to sell well since it was delivered late, plagued with quality issues and soon outperfomed by more capable machines like the Atari ST and the Comodore Amgia which came with a mouse controlled graphical user interface which QL lacked.
Despite its design flaws the machine offered some remarkable features. It comes with a very compact and for its time advanced operating system which provides e.g. preemptive multitaskting. It took the rest of the industry nearly a decade to get that.
I got the QL roughly two years after its announcement and got in touch with more serious programming languages like Forth and C. Actually the Lattice C Compiler from Metacomco was the first C Compiler I used and learned the C-Programming language with it. Delivered on three microdrive catriges it was incredible slow and it was definitely necessary to buy a disc drive in order to actually use it which I did. Interestingly it was possible to use this compiler on a machine with less than 96K of free memory!
The Lattice C compiler is unfortunately not free software and obviously still used on some mainframe systems so it is not available on the web. Since I sold my original QL with my complete software library included, I do not have access to this compiler at moment. Hopefully a friend my mine will help me out later this year.
As an alternative, with C68 there is free and more ANSI-C compliant compiler available which was developed by Dave Walker in 1997. It can be obtained from the Sinclair QL website of Dilwyn Jones which provides an quite extensive collection of documentation and software for the QL. C68 runs exclusively on an QL with the Toolkit II extension from Tony Tebby and an exteneded memory to at least 640KB which is the 'official' maximum configuration. Even with that the combination of the build menu and the compiler itself causes out of memory errors but it is at least possible to compile and link a small application such as snake with a basic compile script which you find included in this package.
Another option is to cross compile C programs for the QL with QDOS-GCC which is basically a patched version of the GNU-C compiler. GNU-C is considered to be superiour to C68 in terms of build and run time efficiency, standard compliance, etc. The QDOS-GCC version however is based on GCC 2.95 which is from today's perspective old as the hills. It is said to be impossible to compile it with any modern version of GCC. I found out the easiest way to get QDOS-GCC up and running is to build it on a virtual machine running a Linux distribution of that age. I used GNU/Debian-Woody pretty successfully for that. The provided Makefile allows the invocation of QDOS-GCC with some additional configuration arguments.
This repository provides configuration files for the autotools build system in order compile or cross compile with a GNU Compiler. Furthermore for illustration purposes the software can be compiled on a physical or simulated QL environment as well. It is desperately slow but it works. The following sections explain how to do this.
Compiling for Unix/GNU-Linux is actually most simple and straigfoward. Use the following commands to configure, compile and install snake on your host machine:
autoreconf -i
./configure
make
make install
The last command installs the snake executable binary file under /usr/local/bin and requires root credentials. Make sure that you have the development version of the ncurses library installed on your system. Under debian this is done with the command
apt-get install libncurses5-dev
Cross compilation requires to compile the QDOS-GCC compiler first. Refer to the website of Thierry Godefroy about howto to do this. As already mentioned the easiest way seems to install a Linux distribution which already comes with the required GCC version 2.95 as in example Debian-Woody. The following instructions are based on that approach.
Debian Woody comes with a very ancient versions of the autotools build script frame work. Luckily non of the core features are really missing. What you need to do is to create some standard documentation files required in GNU software since the option to disable to check them is not available Woody's version of autoconf. Create these with the following command:
touch NEWS AUTHORS ChangeLog
The configure script is generated as usual with the following command. Make sure that you have no artefacts from previous builds in your directory.
autoreconf -i
Then configure the build system and start cross compilation. This requires that qdos-gcc is accissible from your install path:
./configure --build=i386-pc-linux-gnu --host=m68k-coff --enable-qdos CC=qdos-gcc
make
Be aware that you need to add an additional header of 30 bytes to the resulting snake executable file which is required by the QDOS commands exec and exec_w. Since the header seems to be more or less the same for every executable of that type you can copy over the initial 30 bytes from any other function executable and prepend them to your snake binary. You will also find a small C-utility program for adding the QL binary header under the name addqlh.c.
The most unpractical but neverless interesing experience is how it feels like to compile this primitive application on the original hardware. QDOS comes with an unique naming scheme for file names where the file name and the file extension are separated by an underline character. So you need to rename all .c files to _c and .h to _h since otherwise the compiler is not able to locate any source files. You find a shell script which applies the rename operation for all source files which is invoked by the following command:
./rename-sources-for-ql.sh
Afterwards copy over all source files to your QL. If you have an IDE hard disk interface like QUBIDE, you can use the Image Editor Utitily provided by habisoft for this.
To compile snake on the QL first load the basic program 'build_snake_bas' and set the default directories for the C68 program files and the data source files of snake to the corresponding directories. The compilation is started by just starting this basic program with 'run'. The original hardware it is incredible slow and much probably there will be an out of memory error in the linkage phase. The problem can be addressed by reducing the maximum allowed length of C specifiers in the C68 linker source files and recompiling them. If you managed to get to this stage I can provide you a patched version of the linker as well. Just write me an email.
On the QL the snake game is started by the command exec_w followed by the full qualified file name of the snake binary (snake or snake_exe).
The computer plays admittedly a little bit stupid. There are for sure much better ways to implement a more clever computer player but do not forget that the QL platform is quite limited and the ultimate goal is of course to run the application even on a standard QL with 128KB of RAM. Anyway, I am open for any suggestions for improvement.
This implementation code stands under the terms of the GNU GENERAL PUBLIC LICENSE 2.0.
January 2017, Otto Linnemann
Thanks to all the people who helped to keep the QL platform alive and provided documentation and software for it: