Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site oddjob.UChicago.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!ihnp4!gargoyle!oddjob!matt From: matt@oddjob.UChicago.UUCP (Matt Crawford) Newsgroups: net.unix-wizards Subject: Unibus zero vectors on vax/780 Message-ID: <479@oddjob.UChicago.UUCP> Date: Mon, 1-Oct-84 17:40:26 EDT Article-I.D.: oddjob.479 Posted: Mon Oct 1 17:40:26 1984 Date-Received: Wed, 3-Oct-84 08:27:22 EDT Reply-To: matt@oddjob.UUCP (Matt Crawford) Organization: U. Chicago: Astronomy & Astrophysics Lines: 35 We had been getting periodic crashes as the system (BSD 4.2) tried to do a UBA reset. The cause was the internal counter of unibus zero vectors (uba_hd[0].uh_zvcnt) reaching 250000 every 10 days or so. According to our DECmen, there should only be a few zero vectors per day or per week. "Naturally" they suspected the software. After a few months it was made clear that the hardware was responsible. They brought up VMS for a weekend and hooked up a logic analyzer to verify that the BRRVR was in fact empty when read. They have also apparently have tested a system configured similarly to ours and it behaves the same way. You may wish to check your system for this behavior. Our configuration is: 780 cpu with 1 DW, which holds: 1 UDA50 -- 2 RA81's 3 DZ11's 1 RX211 -- seldom used 1 3COM ethernet interface -- (You may be sure that they tried pulling this out.) The zero vectors come fastest when one or both RA81's are active, and high activity on the DZ's seems to increase the rate also. Maybe this is a design flaw in the UDA50? VMS users may never observe this symptom because VMS apparently ignores zero vectors completely. I can't tell you for sure what fraction of the unibus or SBI time is wasted by this problem, but sometimes all terminals halt for several minutes on end while the CPU and disks remain active. This could be related. You can look at your zero vector count with adb via the command uba_hd$