Re: Linux 2.4.17 bug, mmap of /dev/mem

Dan,

Could you elaborate on the problems associated w/ bus timings that
you've seen on the 8xx?  We've been seeing a lot of unexplained Oops
messages (and even crashes) on one of our hardware platforms.  The only
common thread seems to be dereferncing bad pointer values, but they
occur in so many different places...

I've asked our hardware guys to take a look at the settings for the UPM
we are using to control SDRAM.  Do you think we are on the right track?
Can you provide any guidance?

Thanks in advance for any help you can provide!  I'll buy you a beer and
some maple candy the next time I'm up your way! :-)

John

Dan Malek wrote:

David Ashley wrote:

quoted

Maybe you can point me to some discussion of how linux operates? I mean,
once the memory is mapped with the page tables, what happens once the
process does a read to a page? Does that generate a page fault?

It isn't really unique to Linux.  Yes, the access can generate a page
fault, which will cause a kernel exception to load the TLB.  This can
generate some weird looking, early terminated bus timing, which is
perfectly within the specifications of the hardware but isn't something
the designers always consider.  I've seen this quite often on the 8xx,
but fortunately have never had to attach a logic analyzer to a 60x bus.

So, I doubt it is any Linux or software problem, but more likely something
wrong with the timing on the bus that is resulting in incorrect data
returned to a memory access.

--
John W. Linville
LVL7 Systems, Inc.

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