From owner-freebsd-hackers Mon Feb 26 12:37:13 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id MAA14139 for hackers-outgoing; Mon, 26 Feb 1996 12:37:13 -0800 (PST) Received: from covina.lightside.com (covina.lightside.com [198.81.209.1]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id MAA14134 for ; Mon, 26 Feb 1996 12:37:11 -0800 (PST) Received: by covina.lightside.com (Smail3.1.28.1 #6) id m0tr9fH-0009YsC; Mon, 26 Feb 96 12:36 PST Date: Mon, 26 Feb 1996 12:36:56 -0800 (PST) From: Jake Hamby To: Terry Lambert cc: Narvi , phk@critter.tfs.com, hackers@FreeBSD.org Subject: Re: Go SCSI! Big improvement... In-Reply-To: <199602262022.NAA02490@phaeton.artisoft.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-hackers@FreeBSD.org Precedence: bulk On Mon, 26 Feb 1996, Terry Lambert wrote: > Most VLB motherboards have a single bus master slot, the one closest > to the edge of the motherboard. > > Bus master DMA from a VLB controller will not cause the L2 and L1 caches > to be updated/invalidated unless it is in a master slot. > > Not all VLB motherboards have even a single master slot. > > Each VLB transfer steals cycles from DRAM refresh. You can only > steal so many cycles before your system becomes unstable. Generally, > this is the number of cycles stolen by two slots. > > > If you disable your L1 and L2 cache and jumper in more wait states, you > can successfully use 2 VLB devices. > > But then why bother? Interesting.. Because I traditionally have put my video card in the first slot. At any rate, I now have a VLB SVGA card and a VLB busmastering SCSI controller, and my system works (with both caches enabled) so I'm happy, but I wouldn't recommend VLB to anyone else, with PCI motherboards as inexpensive as they are now! Oddly, once I added SCSI, I started getting many CRC errors from my internal modem, and after trying literally dozens of combinations of IRQs and ports, I decided to reset it to the settings I was using before (COM3, IRQ9), and move it to a different slot (one of the VLB slots even though it is an 8-bit card). Now it works fine! Go figure... :-) ---Jake