[ltp] 770ED and Dock SCSI vs hdparm DMA

Ronald W. Heiby linux-thinkpad@www.bm-soft.com
Thu, 30 Nov 2000 12:50:46 -0600

Hash: SHA1

Thursday, November 30, 2000, 5:16:51 AM, James wrote:
> Thats quite an old model... are the IDE drives on the a PCI or IDE bus?
> and how much ram have you got?

Well, it's not *that* old. It's got a 266MHz Pentium II in it. I've
got 128Meg of RAM. The internal HD is IDE. When the system is stitting
by itself, there is no DMA problem. It works fine. When I dock the
system, there is a SCSI controller sitting on the PCI. With that SCSI
controller visible, whether or not configured into the system, IDE
drive DMA is no longer available.

> There is a problem with DMA on IDE buses in that DMA cannot address more
> than the first 16Meg of memory. if you have an IDE bus based system and
> more than 16Meg of ram you may be runnign into this problem, the problem
> is DMA buffers can be allocated and deallocated on the fly however due
> to the linear memory model of linux it might not be possible to get
> space in the 0-16Meg area.

I suspect that this is not the problem, since it's the same HD, same
memory, and same DMA controller whether the system is plugged into the
dock or not.



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