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Path: utzoo!mnetor!seismo!rutgers!ames!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (System Mangler)
Newsgroups: comp.unix.questions,comp.unix.wizards
Subject: Re: uda50 delay settings
Message-ID: <2477@cit-vax.Caltech.Edu>
Date: Sun, 26-Apr-87 01:22:18 EDT
Article-I.D.: cit-vax.2477
Posted: Sun Apr 26 01:22:18 1987
Date-Received: Sun, 26-Apr-87 22:43:35 EDT
References: <147@tijc02.UUCP>
Organization: California Institute of Technology
Lines: 25
Summary: delay settings are there for RK07's, RL02's
Xref: mnetor comp.unix.questions:2038 comp.unix.wizards:2036

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.

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.  Since they
transfer only one word when they get the bus, they can be easily
starved by devices (like the UDA50) that transfer many words per
bus arbitration, even if the RK07/RL02 is at the head of the bus.
Thus, the purpose of the Unibus Delay jumper is to leave lots of
idle bus time for such devices.

The best setting is usually determined by experiment.  Try the
fastest setting, and if you get data lates, try a slower setting.
With some combinations of devices, no setting is slow enough.
(We solved that one by selling both the RL02's and the UDA50's).

I think DEC always sets them to the slowest setting.  The
corresponding DMA speeds are approximately:
	0us	800 KBytes/sec	(same as an RP04, circa 1975)
	6.2us	350 KBytes/sec
	10us	250 KBytes/sec	(half the speed of ST506)

Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck