Re: PATCH: Different SCSI ordering for WIDE SCSI chains.
Paul Slootman (paul@wau.mis.ah.nl)
Wed, 2 Dec 1998 08:54:11 +0100
On Tue 01 Dec 1998, Brandon S. Allbery KF8NH wrote:
> In message <19981201122758.A3415@wau.mis.ah.nl>, Paul Slootman writes:
> +-----
> | 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
> |
> | 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
> +--->8
>
> IIRC, if the host adapter is issuing commands and then disconnecting, a
> narrow device can send a response while a wide device is already talking on
> the bus because it won't see the wide device, resulting in a collision.
This won't happen, because the bus phase will show the narrow device
that it is not free. Using the data bits for selecting a device is only
a very small part in the entire arbitration sequence.
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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