From owner-freebsd-alpha Fri Jan 7 7:42: 6 2000 Delivered-To: freebsd-alpha@freebsd.org Received: from duke.cs.duke.edu (duke.cs.duke.edu [152.3.140.1]) by hub.freebsd.org (Postfix) with ESMTP id 8D97F1522B for ; Fri, 7 Jan 2000 07:41:46 -0800 (PST) (envelope-from gallatin@cs.duke.edu) Received: from grasshopper.cs.duke.edu (grasshopper.cs.duke.edu [152.3.145.30]) by duke.cs.duke.edu (8.9.1/8.9.1) with ESMTP id KAA25241; Fri, 7 Jan 2000 10:41:44 -0500 (EST) Received: (from gallatin@localhost) by grasshopper.cs.duke.edu (8.9.3/8.9.1) id KAA60317; Fri, 7 Jan 2000 10:41:14 -0500 (EST) (envelope-from gallatin@cs.duke.edu) From: Andrew Gallatin MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Date: Fri, 7 Jan 2000 10:41:13 -0500 (EST) To: De la Cruz Lugo Eric Cc: freebsd-alpha@FreeBSD.ORG Subject: Re: HARDWARE.TXT specific for Alpha? In-Reply-To: References: <14453.62608.509835.123219@grasshopper.cs.duke.edu> X-Mailer: VM 6.43 under 20.4 "Emerald" XEmacs Lucid Message-ID: <14454.1900.901358.626546@grasshopper.cs.duke.edu> Sender: owner-freebsd-alpha@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org De la Cruz Lugo Eric writes: > > > On Fri, 7 Jan 2000, Andrew Gallatin wrote: > > > > > Max memory currently varies by platform. On most machines it is 1GB > > and on newer 21264 machines it is 2GB. <..> > > Thanks for the info, in X86 Architecture the RAM max size is 4 GB (check > ftp.cdrom configuration :), i thinked that in Alpha should be bigger. > > i guess im wrong about that :) The problem is that we need to be able to DMA to/from any address is RAM. On most platforms, the default direct-mapped DMA window is 1GB in size, so we cannot exceed 1GB. It is possible to alter the number, size & placement of such windows so as to increase the amount of RAM one can DMA to/from. I have done this for the 21264s which is why they can have 2GB. Another solution would be to set up temporary scatter/gather dma mappings for all DMA & not just ISA DMA. This would alow memory sizes greater than 4GB. This would require changes to many device drivers and all drivers would need to support this mechanism to be able to use it. I don't see this happening any time soon. Cheers, Drew ------------------------------------------------------------------------------ Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin Duke University Email: gallatin@cs.duke.edu Department of Computer Science Phone: (919) 660-6590 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message