From owner-aic7xxx Wed Jul 7 13:31:40 1999 Delivered-To: aic7xxx@freebsd.org Received: from caspian.plutotech.com (caspian.plutotech.com [206.168.67.80]) by hub.freebsd.org (Postfix) with ESMTP id C44721511A for ; Wed, 7 Jul 1999 13:31:36 -0700 (PDT) (envelope-from gibbs@caspian.plutotech.com) Received: from caspian.plutotech.com (localhost [127.0.0.1]) by caspian.plutotech.com (8.9.3/8.9.1) with ESMTP id OAA04924; Wed, 7 Jul 1999 14:30:55 -0600 (MDT) (envelope-from gibbs@caspian.plutotech.com) Message-Id: <199907072030.OAA04924@caspian.plutotech.com> X-Mailer: exmh version 2.0.2 2/24/98 To: Karl-Heinz Herrmann Cc: "Justin T. Gibbs" , aic7xxx@FreeBSD.org Subject: Re: multi scsi questions In-reply-to: Your message of "Wed, 07 Jul 1999 19:13:46 +0200." Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Wed, 07 Jul 1999 14:30:55 -0600 From: "Justin T. Gibbs" Sender: owner-aic7xxx@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org > The priority, from highest to lowest, is >> as follows: 7->0, 15->8. When a device with an ID lower than 8 >> arbitrates along with a device with an ID greater than 7, the device >> with the high ID knows that it has lost the arbitration and will get >> off the bus. >But from this seems to follow: If there is a device ID 9 and a narrow >device on ID 1 (ID 2 was a typo anyway) the wide device ID 9 recognises >it will loose arbitration and free the bus for an access to device ID 9. >So it won't work. >Or does the high device recognise the call for ID 9. Think of the arbitration like this: Low Byte High Byte XXXXXXXX XXXXXXXX ----------------- 01000000 10000000 This is what an arbitration for the bus might look like. The device at id 1 cannot see that id 8 is also arbitrating. So if they both pop up during the same arbitration cycle, id 8 will bow out. Luckily, SCSI devices don't want to have the bus all the time, so ID 8 will win some other time and then take the bus. The BSY and SEL lines are seen by all devices, so ID 1 can tell if the bus is busy or that it is too late to participate in an arbitration cycle, so there is no conflict. >Especially since I do have a setup with 2940UW and both narrow and wide >devices -- and the Low ID's start to get crowded :-) >Could I indeed switch both wide harddrives from their ID's 1 and 6 to >ones above 8 and still use the (ID-8) by a narrow device? Certainly. >There were at least strong recommendations never to try that. Some >people had it working but others said it's just because some UW devices >are consistently faster and actually win the race. It may be that some wide devices are buggy, but if they follow the spec and your bus isn't too long (meaning the bus skew delays for the signals violate the spec) you should be okay. -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message