Oh, No! Jag has Hardware Problems!
Pink floyd like 2 play 3DO
#: 64750 S15/Jaguar General
21-Dec-94 05:47:55
Sb: #John Carmack on JagDoom
Fm: Neil Jenkins 100265,1327
To: All JagDoomers
The following is John Carmacks view on JagDoom, It makes interesting
reading:)
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From: John Carmack <jo...@idcube.idsoftware.com>
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Subject: JagDoom
>how the Jag coped with Doom. etc..
Developing on the Jag started out fun, but pushing the jag hard
started showing up some architectural problems.
The system suffers from a critical lack of balance. The central
processor is well over an order of magnitude slower than the risc
chips, but the risc chips are not suited to running the entire
program because of their small fixed code memories.
There is quite a bit of power there, but you have to go through
contortions to get a lot of it.
The worst problem is that the system has some hardware flakyness when
all the processors are banging on the bus at once. This is what
causes the network errors (they aren't really network errors, they
are game errors that show up by different things happening on the two
systems). In hindsight, I should have just run the net game without
all the processor overlap. It runs a good deal slower, but it
doesn't get the errors.
Of cource, I would do several things differently if I was doing the
project again. I know for sure how to make the rendering code 50%
faster. This would allow you to either increase the horizontal
resolution from 160*180 to 256*180, or increase the speed to 20 fps
from 15, or run totally full screen at the same resolution with a
more complex world.
The problem is that Jag DOOM usually becomes speed limited by the
game logic, not by the rendering code. The problems of movement
clipping and line of sight calculation for all the monsters are more
difficult to run efficiently on the risc processors. The basic actor
logic is too bulky and spread out to run on one of the risc chips,
but it is really a bit too much for the 68k to handle when the
rendering is taking up most of the bus bandwidth.
We are not working on any more jag projects at the moment (Quake is
taking up all my time). We gave Atari a lot of our time and effort,
and we are now in a "wait and see" mode. If they hit their sales
projections, we will probably do something else late next year. We
are probably going to license the jag DOOM code to some other
companies though, so you might see a similar game before that.
John Carmack