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1996-01-25
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# -------------------------------------------------------------------
# JAGUAR (c) Copyright 1996 Nat! & KKP
# -------------------------------------------------------------------
# These are some of the results/guesses that Klaus and Nat! found
# out about the Jaguar. Since we are not under NDA or anything from
# Atari we feel free to give this to you for educational purposes
# only.
#
# Please note, that this is not official documentation from Atari
# or derived work thereof (both of us have never seen the Atari docs)
# and Atari isn't connected with this in any way.
#
# Please use this informationphile as a starting point for your own
# exploration and not as a reference. If you find anything innacurate,
# missing, needing more explanation etc. by all means please write
# to us:
# nat@zumdick.rhein-main.de
# or
# kkp@gamma.dou.dk
#
# If you could do us a small favor, don't use this information for
# those lame flamewars on r.g.v.a or the mailing list.
#
# HTML soon ?
# -------------------------------------------------------------------
# $Id: general.txt,v 1.5 1996/01/25 22:12:06 nat Exp $
# -------------------------------------------------------------------
No gospel contained here !!
A couple of general notes on the Jaguar. Please note about the bitness
issue, that this is just our general take of the scene. The bitness
is the way the chip 'feels' like (to us).
The Jaguar consists of these major parts:
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
a) 16/32 bit 68000 processor that is used to bootstrap the system.
Feels like a 32bit chip (in many respects) with a 16 bit
memory interface
b) 32/64 bit GPU risclike processor that is the 'heart' of the
system. The chip feels like a 32 bit chip with an 64 bit
memory interface. This one has 4Kbytes of local memory for
instruction and data.
c) 32/32 bit DSP chip, also risclike. Has a 32 bit memory interface
and 8KB of local memory for instruction and data.
d) a 64 bit objectprocessor (OP) that feeds the video chip
e) a 64 bit Blitter
Input/output stuff:
=-=-=-=-=-=-=-=-=-=
a) A videochip capable of displaying 16bit Cry/RGB or 24bit RGB
pixels. Tightly coupled to the OP.
b) Digital joystickinterface + 2 ADCs on the joystick ports
for analog input.
c) 2 16bit DACs for sound production
d) Serial communications channel
Systemstructure:
=-=-=-=-=-=-=-=
Consider the Jaguar to be the GPU, the OP, the Blitter, the memory
and the videochip.
You got here a 64 bit system communication thing happening. All
data is passed along the bus in 64 bit quantities (also known as
a phrase). Since you can pass data around the bus at a speed of
ca. 13.3Mhz (?) you get a thruput of a little more than 100MB/s.
The RAM is monolithic, in that there's no division between VideoRAM
and normal RAM. Usually the OP fetches the data from memory scanline by
scanline and stuffs it into two small videochip linebuffers. The
videochip only fetches data from there. It does not have access to
the main memory.
There are "gateways" out of the main system to connect peripheral
chips to it. There are two 32 bit gateways one to the DSP and one
to the ROMs and a 16 bit gateway to the 68000. Since the 68000
doesn't have a cache, just keeping it running in an idle loop
will probably impede maximum performance of the system.
The gateways are most probably unbuffered, which would mean that
a 16 bit access by the 68000 is just as costly as a 64 bit access
by the GPU.
The DSP is connected/integrated with some peripheral devices,
that provides serial communications capability, joystick interfacing
and hardware timers.
Endianness: **** WARNING: High Bullshit content ****
=-=-=-=-=-=
[ The endianess shit is my fault. Klaus surely doesn't want to be
associated with this (nat/1996) ]
Bytes are just bytes
Word are two bytes, one being the MSB and the other being the LSB
(most significant byte, least significant byte)
Long words consist of four bytes, being MSB NSB ISB and LSB.
(Most, not so, insignificant, least)
Phrases consist of eight bytes
MSB HSB VSB RSB QSB NSB ISB LSB
(Most, highly, very, really, quite, not so, insignificant, least)
The Jaguar is a bit strange mixture of endianness schemes.
The 68K thinks in Motorola terms MSB NSB ISB LSB (most significant byte,
not so significant byte, insignificant byte and least significant byte)
The OP thinks in terms of ISB LSB MSB LSB occasionally, for example
when using addressses, but also the right, Motorola way when examining
phrases: MSB HSB VSB RSB QSB NSB ISB LSB.
The GPU seems to be configurable in its endianness.
Bandwidth:
---------
106.4 Mio bytes/s or 101.5 MB/s MB as in 1024*1024 bytes/s
13.3 Mio phrases/s