Date: Mon, 26 Feb 1996 12:36:56 -0800 (PST) From: Jake Hamby <jehamby@lightside.com> To: Terry Lambert <terry@lambert.org> Cc: Narvi <narvi@haldjas.folklore.ee>, phk@critter.tfs.com, hackers@FreeBSD.org Subject: Re: Go SCSI! Big improvement... Message-ID: <Pine.AUX.3.91.960226123254.5298C-100000@covina.lightside.com> In-Reply-To: <199602262022.NAA02490@phaeton.artisoft.com>
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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
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