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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: uda50 delay settings
Message-ID: <6467@mimsy.UUCP>
Date: Sun, 26-Apr-87 15:53:59 EDT
Article-I.D.: mimsy.6467
Posted: Sun Apr 26 15:53:59 1987
Date-Received: Sun, 26-Apr-87 23:51:32 EDT
References: <147@tijc02.UUCP> <2477@cit-vax.Caltech.Edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 39
Xref: mnetor comp.unix.questions:2044 comp.unix.wizards:2041

>In article <147@tijc02.UUCP>, seb022@tijc02.UUCP (Scott Bemis) writes:
>>I would like to know the lowest delay settings
>>I can set on my UDA50 disk controllers.

In article <2477@cit-vax.Caltech.Edu> mangler@cit-vax.Caltech.Edu
(System Mangler) writes:
>Some DEC Unibus disks, such as the RK07 and RL02, have buffers too
>small to hold an entire sector.  They suffer data late errors if
>they don't get at least half of the Unibus bandwidth. ...
>Thus, the purpose of the Unibus Delay jumper is to leave lots of
>idle bus time for such devices.

>... With some combinations of devices, no setting is slow enough.
>(We solved that one by selling both the RL02's and the UDA50's).

The 4BSD Unibus allocation code understands `bus eater' devices
like RK07s, and will lock all other devices out of the Unibus while
the bus hog is using it.  I believe the RL02 driver is not marked
as an exclusive-Unibus-use device, but that is a trivial change.
The problem is that the stock 4BSD UDA50 drivers ignore the bus
lock out protocol.

If you run 4.3BSD and suffer with UDA50s and RK07s and/or RL02s,
you can install the driver I posted to net.sources a few weeks ago,
or (for ARPA sites) FTPable from host mimsy.umd.edu as uda50/4.3.shar.
This driver honors the bus lock protocol, and you can set the delay
down to zero.

> 	0us	800 KBytes/sec	(same as an RP04, circa 1975)
>Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck

I only get 750KB/s.  Still, that is not too awful.  Alas, actual
throughput from any one drive never seems to rise above 125KB/s,
because of the delays for seeks and head switches.  Just think:
another 13 RW amplifiers per RA81, and actual throughput would
probably double.  But DEC must have saved perhaps $50 per drive....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu