From: neil@cs.hw.ac.uk (Neil Forsyth)
Newsgroups: comp.sys.atari.st
Subject: Re: TT Compatability questions
Keywords: TT, ST, compatible, games, applications
Date: 10 Sep 92 08:43:47 GMT
Organization: Dept of Computing & Electrical Engineering, Heriot-Watt University, Scotland

In article <H.R5av1hwO5UM@fredrik.atari.no> jornmoe@fredrik.atari.no writes:
>In <1992Sep7.090500.20341@cs.hw.ac.uk>, Neil Forsyth writes:
(lots of very true statements deleted for brevity)
>>I view the TT as being to the ST what 486DX-33 PC's are to 386SX-16 PC's.
>>They are every bit as commercial. If you buy a PC game these days you can bet
>>it will work on any PC. This should be true of ST games on the Falcon.
>
>This comparison is not good! The only difference between 486DX PC's and 
>386SX PC's is the processor. The rest of the machine is the same! The ST is a
>machine designed as a keyboard home-computer. The TT is based upon the hardware
>of the ST, but have essential additions to make it more 'business'-oriented.
>Like internal harddisk, VME-bus, SCSI-bus, higher resolutions, LAN port etc.

PC's are not the same! Gawd! They've got different video cards, memory
management, processors, mice, DOS, BIOS. In fact the use of the BIOS in PC is
almost essential to insulate you from the various hardware configurations.
There are some notable exceptions such as the keyboard and 'standard' video.

Notice how the PC version of Speedball 2 works on loads of PC's and can be
installed on the hard disk but the ST version does not work on the TT or
Falcon and can't be installed on HD. Bad coding in the disk department?

>>To sum up, I have tried running a *LOT* of ST games on a Falcon and less than
>>10% of them worked. This is one reason I think the Falcon will fail if
>>marketed as a games machine. The available leisure software will be small.
>
>Only 10%? Whether this is bad or not depends uppon the quality of these games!

Many were the best of the latest releases. The spread (if you can call it
that :-) of games that did work dated from 1986 to the present day.
Speedball 2 didn't work but Archipelagos did (8Mz no cache).

>>Only a couple of the games worked after disabling the cache and setting
>>the speed to 8Mz. Since most games that load from a bootsector and don't use
>>system calls failed I assume that they were not 68030 compatible.
>There is only two things a programmer can do which a proper written trap-
>handler on the 68030 can't handle to make it 100% compatible (with cache off). 
>Those things are speed depended code and self written trap routines!!

Most of the speed dependant code was in the DMA routines.

One of the reasons the games often crashed on the 68030 was their test for
being in Supervisor mode. This was usually part of the copy protection.
They used the MOVE SR,Dx instruction which on the '030 is privileged.
They could have used the GEMDOS Super call ($20) to find that out. Strangely
if they found they were in User mode they used Super to change. However the
protection heavily depended on using the trace exception which caused it
to fail on the 68030.

Another common error is to load code/data at low absolute addresses that
flattens OS workspace. Even seven years on some programmers still do this!
Fixing your screen memory at $78000 is also a problem. With TOS demanding
more low memory there is the risk that programs will bang their heads on their
own video RAM. OK that would be a bummer on a 512K machine anyway.

>>Atari were not to blame for these incompatibilities however I do blame them
>>for not kicking butt when the TT didn't run software. Programmers should have
>>learned their lesson back then.
>
>Actually we agree on the lousiness of game-writers. I do howewer think
>that the Falcon is as ST(e) compatible as the MSTE (with cache and 
>16MHZ on) but with additonal problems with trap's as mentioned above!

Bad coding is not just the domain of the game writers. It's sad to think that
these bad coders will hurt sales of the Falcon which so desperately needs
software.

>PS. Do you have a Falcon???

Maybe. I can't say. I am a developer though.

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! DISCLAIMER:Unless otherwise stated, the above comments are entirely my own !
! Neil Forsyth                                                               !
! Department of Computing and Electrical Engineering                         !
! Heriot-Watt University                                                     !
! Edinburgh, Scotland                                                        !
! United Kingdom            Email: neil@uk.ac.hw.cs, ..!ukc!cs.hw.ac.uk!neil !
! "'Have you got any?' he asked, expecting the answer no" - Monty Python     !
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