Messages in this thread | | | Date | Wed, 31 Oct 2007 14:28:11 -0700 | From | "Ray Lee" <> | Subject | Re: How to debug complete kernel lock-ups |
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On 10/31/07, John Sigler <linux.kernel@free.fr> wrote: > "It seems that the PCI clock on this system has a rather large over- and > undershoot and we suspect that the undershoot (of ~1V) is causing a drop > in the core voltage of the on-board FPGA which results in lockup of the > firmware. Both the under- and overshoot are well outside the allowed > ranges (high=VCC+0.5V and low=-0.5V) of the PCI specification and a > premature conclusion might be that the system does not comply to the PCI > spec and that this is the cause of the lockup on this PC." > > This is waaay out of my league, as my area is software. > > Is it typical for voltage issues to hang hardware?
Yes, if the voltage is applied (or lacking) at the right place.
> Is it typical for one PCI board locking up to nail the entire system?
This doesn't appear to be a case of the *board* crashing, but rather the board taking the pci bus and related hardware on-motherboard down with it. Once that's down, anything that you need that goes through the bus (on a PC, that's pretty much everything), is inaccessible.
> I don't understand why the lockup would only happen when I write to the > 4 ports within a small time frame, and not when I only write to 2 ports > (either one port on each card, or 2 ports on the same card). I suspected > some kind of concurrency issue...
No, given the hardware guy's description, it's a power issue. Perhaps when you're writing to a port, you're using more power on the card? Four ports = 4 * the power draw. When the current load increases, voltage drops, and if you underpower a chip, it's going to lose its little head.
> I suppose the next logical step is to get the board's engineers > and the system's engineers duke it out? :-)
Yes, all signs point to it being a pure hardware issue. You may be able to work around it in software by initializing a 'counting semaphore' to 2 to manage the maximum concurrency, so that you'll never write more than 2 ports at a time until the hardware guys figure it out.
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