On Thu, 14 Aug 2003, Paul Sommerhein wrote:

> Lennart Augustsson <lennart@augustsson.net> writes:
>
> > Yes, DMA can still happen while interrups are off.  On the PCI bus any
> > bus mastering device can do cycles.  E.g., if you have a USB
> > controller it will access memory every ms regardless of any transfers
> > that have been set up.
>
> Thanks!  So you are saying that if I disable USB support in the kernel
> the controller will still do cycles?

As Jachym noted, if the chip is not enabled, no cycles. I think Lennart
was indicating that you could still have PCI bus activity even if you
weren't sending anything out the driver.

But what exactly are you trying to do? In real usage, you will have these
other bus masters using the PCI bus, so a timing value that averages over
them will represent a real use case. If you shut everything down, you can
get a pure theoretical number, but it will have little bearing on real
usage.

Take care,

Bill