From owner-aic7xxx  Fri Dec  5 13:50:00 1997
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From: gibbs@narnia.plutotech.com (Justin T. Gibbs)
Subject: Re: does aha2940UW work with Seagate LVD disks?
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To: stevebr@primenet.com (Steve Brueggeman)
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In article <348622ea.343750@pop.primenet.com>,
	stevebr@primenet.com (Steve Brueggeman) writes:
> On Tue, 2 Dec 1997 15:49:11 -0200, you wrote:
> 
> I believe that all Seagate ultra2 drives support both Single Ended, and Low
> Voltage Differential.  The drives switch automatically according to the
> diffsense line.

This is true.

> But, Single Ended mode does not support 40Mhz transfers (80MB/sec on a wide
> interface).  Single Ended mode only supports Ultra-1 (20Mhz or 80MB/sec on
> wide interfaces).  To get 40Mhz transfers, you need a host adapter that has
> LVD drivers.

Single Ended mode will support 40MHz transfers, but the cable length must
be so short that you would only be able to put one or two devices on the
bus.  I do not know if the devices will be so annoying as to not negotiate 
40MHz if you ask for it and diffsense is false.  I certainly hope not, as
there are certainly systems that are single target/single initiator where
cable length is not a problem, but the number of signals wires is.

> The chip they are using appears to be an AIC7890 and an AIC3860.

Both the 7890 and the 7891 support single ended Ultra2.  You must use
the aic3860 to convert the single ended bus to LVD.  The 7890 is a
32bit PCI chip and the 7891 is a 64bit chip.

> I have no idea if this is currently supported under Linux or not.

Neither are supported by Linux currently, but they should be supported
in the near future.  The 7890, 7891, and 7895 have a few register changes
that must be dealt with for the driver to work.  I have a 7895 working
here under FreeBSD and I expect to have the other two chips working as
soon as my eval boards show up.

> Steve Brueggeman.

-- 
Justin T. Gibbs
===========================================
  FreeBSD - Turning PCs into workstations
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