Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mit-eddie!husc6!purdue!decwrl!frambo.dec.com!schabacker
From: schabacker@frambo.dec.com (CB, posted by generous Tim)
Newsgroups: comp.sys.amiga
Subject: Re: 2090 Problems
Message-ID: <8806271729.AA09868@decwrl.dec.com>
Date: 27 Jun 88 17:29:15 GMT
Organization: Digital Equipment Corporation
Lines: 54


> [Various people complaining about problems with hard disk access
> while having overscan/hires (deeper than 3 bitplanes) screens in
> front]

Well, as mentioned in my introducing message, I have a 2090 with a
70MB Micropolis and a 20MB Epson hard disk connected to it. And as
you people might know, we have the PAL video norm over here, giving
you a MINIMAL vertical overscan of 56/128 lines compared to NTSC. 
I experienced the problems descriped, too. First let me say that this
problem is only present when working with 4 bitplane (or deeper ) med-res/hi-res (min. 640 pixels wide) screen in front, which
has some or sometimes NO overscan, due to Chip-DMA (Agnus, that ole
lady) colliding with the DMA from the 2090. Well, it's really the
hddisk.device in ChipMem not getting enough CPU cycles to do it's
job, but read on.

Here is what I did to get rid of it:

1. First make sure that your hddisk.device doesn't get into ChipMem or
pseudo ChipMem ($C00000-$C80000) on A500/B2000's.
So place a "fastmemfirst" or "slowmemlast" BEFORE the "binddrivers"
in your Startup-Sequence. (This was mentioned some time ago by Andy
Finkel)

2. Then you might do some trick that I found to work most of the time,
even BEFORE I did #1. Change your preferences, so that your Workbench
starts at the leftmost position. This seems to help by some magic to
relieve some of DMA strain. Don't ask me why (Jay?).
This works only with programs that "clone" the Workbench screen like
ProfPage, SuperBase Professional, Shakespeare, etc.

The 2090 is the fastest Amiga HD controller I've seen so far, really
nice design, no comparison to C-Ltd. I have a long list of diskperfs
available, if inquiring minds wanna know. :-)
My Micropolis tops ie. at 238312 bytes/sec read and 174762 bytes/sec
write (FFS 34.76 on gamma7)  . And that's an ST-506 drive!!!

- 

P.S.
Could someone please e-mail me the newest version of hddisk(.device)?
Mine is Version 33 (rev 37) (Mon Oct 26 11:06:14 PST 1987), a little
bit out of date, no?

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