usb and too much memory?

[Tony Nelson]

At 6:33 AM -0400 7/15/06, Tom Horsley wrote:
>On Sat, 2006-07-15 at 15:42 +1200, Hadders wrote:
>> Tom Horsley wrote:
>> > On Fri, 2006-07-14 at 21:52 -0400, Tom Horsley wrote:
>> >
>> > > Is there some known problem with > 2 gig of memory and
>> > > the onboard usb with the x86_64 kernels?
>> > >
>> >
>> > Sure enough, when I take out the extra gig of memory,
>> > the scanner starts working and the boot time USB errors
>> > go away. I guess I have a spare gig now (which is all
>> > it really was before - I just thought I'd put it to
>> > use :-).
>> >
>> >
>> It's often been an historical fact that PC chipsets (not server class)
>> often don't like addressing large amounts of memory and require
>> particular DIMM configurations.
>> They also get fussy about EXACT memory timings. Check your mainboard
>> manual (asus are good for providing this as a download) for
>> recommendations on what banks can be used to get to 3GB.
>
>Oh, I did all that. The memory has identical timing and
>the i386 kernel as well as memtest86 has no problems, it
>is only the x86_64 kernel that has USB troubles. I suspect
>some sort of IOMMU nonsense, but the simplest fix is to
>just leave only 2 gig in the machine in any case.

Another test is to install the new memory in place of (some of) the old
memory, so that there is 2 gig installed.  If that works, then it's really
likely to be the amount of memory; if it doesn't work, then it's probably
the memory itself.
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