Date: Wed, 07 Jul 1999 22:53:53 +0200 (MET DST) From: Karl-Heinz Herrmann <k.-h.herrmann@fz-juelich.de> To: "Justin T. Gibbs" <gibbs@caspian.plutotech.com> Cc: aic7xxx@FreeBSD.org Subject: Re: multi scsi questions Message-ID: <XFMail.990707225353.k.-h.herrmann@fz-juelich.de> In-Reply-To: <199907072030.OAA04924@caspian.plutotech.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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 <k.-h.herrmann@fz-juelich.de> 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?XFMail.990707225353.k.-h.herrmann>