Feature: 68K Programming Guidelines
Posted by Nick on 26 April 2000, 01:42 GMT
François Revol, a French programmer, brings up some interesting points in our next feature, talking about establishing guidelines for coding in 68000 assembly.
Ti68k open programming guidelines
With the increasing number of z80 based TI calcs, we have come to an incredible list of shells, at least 3 for every model, each having it's own 'API'. Of course, some of them were designed to be compatible with others like CrASH for Ash... But it's far from ideal.
Of course, on the 68k scene, there are only 3 models (but how many ROM versions ? How many Hardwares ?) but it might change in the future... And don't count on TI engineers to help you to stay compatible...
One project that will help us (IMO) is [tie], which would allow to fill the gap between the Ti92 and the 92+/89 models... I think the most important function needed is heaplock, which must be in the ROM, but we need to locate it.
Another project that I think is the best thing that happened to the Ti68k world since Fargo is Prosit. Multitasking on the is a great and fun thing. And it's only the beginning.
The main reason Prosit isn't so popular is the fact it doesn't allow DoorsOs programs (games particularly) to be loaded (and so multitasked). The problem is DoorsOs progs, DoorsOs itself and TI'ROM aren't designed for that. The keyboard is the perfect example: every program reads the keyboard port directly.
The best design would be to isolate all hardware access in libraries (and even the ROM calls like file access, ...) so that, by changing a library, manually or even within an exec() function, we could run a program both under plain DoorsOs and Prosit, and [tie]. (Another great thing would be porting Prosit to [tie] when it gets enough stable...).
Another problem is the link: There is the standard cable, the IR-Link, the HF-Link... Wouldn't it be good if the progs could access any of these devices without any change ? The neat thing would be a networking protocol which should drive indifferently a 2 calcs cable, an IR net, or an I2C wired calc net. It is on my project list.
An important point is the language: since we are now able to use C or Pascal instead of ASM, it is possible that a library written in ASM will be used by a C program, or be replaced by a new version written in C. So it is important to always follow the C calling convention (even TI engineers do it !) for library calls at least.
Another step will be writing a C standard library, which would allow porting nice programs from the UNIX world... It is also on my project list ;-)
All these stuff would allow both DoorsOs/[tie] and Prosit to run a program.
An example would be a program which uses grayscales. Under DoorsOs it uses the standard gray4lib. Under Prosit it calls a special gray4lib which tells Prosit to allocate a virtual screen and disable the GUI untill a hotkey swaps to an other screen...
Modular programming is sometimes harder to get used to, but I think it is worth to. Something I use in my progs is to include a file named "config.h", common to all progs, in which a CONFIG.BAT writes the target (92/92+/89), the language (English, French,...), and I have a structure MAKE.BAT tree to help build the progs (Have a look at prosit_apps.zip, there is also a nice Othello game for Prosit in bonus).
Last thing: don't assume your programs will be compiled under DOS/Winblows! I had so many problems with DOS specific stuff under Linux... I still don't understand why so much people bother using DOS/Zin, as Linux is so great... :-((
My ultimate goal is to be able to surf the net on a TI (I mean not using any trick like Telnet83, but a real TCP/IP stack and stuff). What about you folks, do you think it is possible ?
I suggest the following to be discussed as a "Ti68k Open Programming guidelines" Request For Comment (RFC ;-))
- Be as modular as possible
- Try to comment the source code (I know it's hard to do)
- Always use the C calling convention
- Isolate I/O in libraries
- Try to think of possible 'wrappers' on ti92 for something that doesn't exist.
- Think about both 92 and 89 screen/keyboard
Well, what do you people think?
Talk amongst yourselves :-)
