386/ix: cpio to floppy panics kernel

Sun Oct 2 05:01:11 AEST 1988

In article <455 at redsox.UUCP> campbell at sushi.UUCP (Larry Campbell) writes:
>I'm running Interactive's 386/ix on a Dell 310.  On the whole it all works
>just fine, but there's one showstopper of a bug:  using cpio to back up
>the disk to floppies panics the kernel with a memory parity (NMI) trap!
>
>Now, I don't really suspect the memory since everything else works fine.
>...
>I can't do backups...  I can feel Murphy breathing down my neck...

You are damn right to feel Murphy breathing down your neck, because this
kind of problem DOES indicate a memory problem with the Dell 310.

The problem (in general) is that not all memory accesses are equally
critical. Accessing memory in some specific order can generate parity
errors or worse if your memory does not safely give the memory chips
enough time to respond. All these new cranked-up 286 and 386 boxes are
pushing things BEYOND their limit. You can run DOS for years, or memory
diagnostics for years and never find a problem, yet your unix tries just
the kind of access which fails. It is not surprising that IS cannot
reproduce the problem on another machine. I have seen this problem before,
many times I must add, and in general there is only one solution: either
replace the memory chips by faster ones or lower the clock frequency.
Your system seems not to run safely at its top speed, because the MMU
sometimes does not give the memory chips enough time to respond. (Our
supplier has often been able to solve our problems by replacing the memory.
It REALLY works.)

I am not blaming Dell specifically here, because many companies make the
same error. Since memory is expensive they just put in slower chips than
the machine really needs. I hope they are listening?????????

Paul.