Re: PATCH: Different SCSI ordering for WIDE SCSI chains.

Paul Slootman (paul@wau.mis.ah.nl)
Tue, 1 Dec 1998 12:27:58 +0100

In article <3662D55D.A31769E5@airways.com> lancer@airways.com wrote:
>
>When mixing narrow and wide devices you must only use the first eight
>scsi ids. If you don't, scsi arbitration will not work correctly. The
>scsi bus uses the data bits to arbitrate for the bus. A narrow device
>does not see the upper eight arbitration bits and can fowl things up.
>Your wide devices can still work in wide mode, but their addresses
>should be set between 0 and 7 where the narrow devices can see them for
>arbitration.

This is not true. Your narrow devices will simply see that they are not
selected when one of the wide devices on address 8 and up is selected,
and ignore it. As long as you keep your adapter on a low address, all
will be well (unless you want to initiate direct transfers between two
devices, but if you're doing that, you know what you're doing anyway).

So, using wide devices on addresses 8 and up is NOT a problem, even if
you use narrow devices as well.

Paul Slootman

-- 
home: paul@wurtel.demon.nl | work: paul@murphy.nl | debian: paul@debian.org
http://www.wurtel.demon.nl | Murphy Software,   Enschede,   the Netherlands


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