Date: Fri, 7 Jan 2000 10:41:13 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: De la Cruz Lugo Eric <eric@iteso.mx> Cc: freebsd-alpha@FreeBSD.ORG Subject: Re: HARDWARE.TXT specific for Alpha? Message-ID: <14454.1900.901358.626546@grasshopper.cs.duke.edu> In-Reply-To: <Pine.BSF.4.10.10001070928460.83671-100000@iteso.mx> References: <14453.62608.509835.123219@grasshopper.cs.duke.edu> <Pine.BSF.4.10.10001070928460.83671-100000@iteso.mx>
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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
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