From owner-aic7xxx Wed Jul 7 13:54:10 1999 Delivered-To: aic7xxx@freebsd.org Received: from fz-juelich.de (zam115.zam.kfa-juelich.de [134.94.172.39]) by hub.freebsd.org (Postfix) with ESMTP id A473415482 for ; Wed, 7 Jul 1999 13:53:59 -0700 (PDT) (envelope-from mod017@mod011.mod.kfa-juelich.de) Received: from mod011.mod.kfa-juelich.de (mod011.mod.kfa-juelich.de [134.94.104.39]) by fz-juelich.de (8.8.8/8.8.8) with SMTP id WAA21191; Wed, 7 Jul 1999 22:53:55 +0200 (MET DST) Received: by mod011.mod.kfa-juelich.de ; id AA04224; Wed, 7 Jul 1999 22:53:54 +0200 Message-Id: X-Mailer: XFMail 1.3 [p0] on OSF1 X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit Mime-Version: 1.0 In-Reply-To: <199907072030.OAA04924@caspian.plutotech.com> Date: Wed, 07 Jul 1999 22:53:53 +0200 (MET DST) X-Face: C^7Es;X;]Sk{&>U>?\JETBAqWr>]MxlJlQ^P<__b.w^4~w6&mMa|J{>D7X[di0@j\$6lRBW p/ejwDm%K*jt|4shxAFeuSP6-3KZ_LO`a+HGjK>@"R!X%U^>mSoh!RmsC[UV@Kv2>{7H4^=YA]NZhZ ,l0M]|y\^cyjJs Organization: Forschungszentrum Juelich From: Karl-Heinz Herrmann To: "Justin T. Gibbs" Subject: Re: multi scsi questions Cc: aic7xxx@FreeBSD.org Sender: owner-aic7xxx@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Hello Justin, thanks for the explanation below. On 07-Jul-99 Justin T. Gibbs wrote: > 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. It seem I have no real idea how this arbitration works. Do the devices look from time to time if there is something? I thought of it more like: The adapter sends a request, all are listening but only the one with the right ID is responding. So what happens when the adapter asked for a high ID and the devices bows out? Has the adapter to repeat the request? Is there a delay in transfer? And why doesn't the narrow device react. It sees only the Low Byte -- so there is his own ID number, and the Wide device left the Bus to the narrow device, so the Bus is not busy. > 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. Does the SEL ine tell the devices that there is some request? And then they all have a look if it's for them? >>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. If my narrow devices keep piling up like now, I will soon have to try that. The cabling is quite short (everything internal) so it will hopefully work from that side. I will keep in mind the 1.5m and the 10cm(?) in between. :-) Karl-Heinz ---------------------------------------------------------- E-Mail: Karl-Heinz Herrmann Date: 07-Jul-99 Time: 22:42:54 ---------------------------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe aic7xxx" in the body of the message