Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!uwm.edu!zaphod.mps.ohio-state.edu!mips!bridge2!jarthur!nntp-server.caltech.edu!tybalt.caltech.edu!toddpw
From: toddpw@tybalt.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Faster IIGS
Message-ID: <1990Oct2.101720.9282@nntp-server.caltech.edu>
Date: 2 Oct 90 10:17:20 GMT
References: <517@fawlty.towers.oz> <8b0r1dS00Vop8FoFlI@andrew.cmu.edu>
Sender: news@nntp-server.caltech.edu
Organization: California Institute of Technology, Pasadena
Lines: 30
Nntp-Posting-Host: tybalt.caltech.edu

cs4w+@andrew.cmu.edu (Charles William Swiger) writes:

>The //gs uses a 16.7 MHz crystal for the basic system timing, I think,
>and each processor cycle takes 6 ticks of the crystal to complete. 

Not quite; the master crystal is 28.63636 Mhz exactly (within tolerance) and
each CPU cycle is 10 ticks of that clock. The 28 Mhz is needed for the new
video modes.

>There is also an odd timing problem that forces the 65th processor cycle
>to be delayed.

It is not a problem; in fact it was one of Woz's many hacks in the original
][ and it prevented the video from having different colors on even and odd
lines of the video. The stretched cycle occurs at the end of each video line
and is there to make each line an even multiple of the color reference
(3.58 mhz or 280 ns).

This delay is only present in the 1 Mhz side of the machine and it does not
affect the CPU unless it is accessing the 1 Mhz side when the stretched cycle
occurs.

>You're exactly right that having the motherboard sped up would be faster
>than using a transwarp, that, as you said, uses caching to run the first
>2 banks at a faster speed than the rest of the system.

Hmm? The transwarp is supposed to accelerate program code in any bank.

Todd Whitesel
toddpw @ tybalt.caltech.edu