PCI UDD Questions

Jeff Webb w1 at codecraftsmen.org
Fri Mar 8 02:19:02 CET 2019


On Wednesday, March 6, 2019 11:38 AM, Jan Kiszka <jan.kiszka at siemens.com> wrote:

> On 06.03.19 12:24, Philippe Gerum via Xenomai wrote:
>
> > On 3/2/19 1:25 PM, Jeff Webb via Xenomai wrote:
> >
> > > I could also avoid using the PCI command register entirely and just write to a device-specific mask bit in my peripheral, but I would rather implement a generic solution if there is not a performance penalty for using the PCI command register.
> >
> > I don't think that using the PCI layer would be cheaper than tweaking
> > some bit in your device. The former involves a serialization on
> > pci_lock, then a read-update-write sequence to send the
> > masking/unmasking command to the bus layer. Sending the acknowledge to
> > the device in order to stop it from interrupting is the usual way for rt
> > sources.
>
> Plus PCI config accesses (which are needed for generic INTx masking) are
> generally more expensive than device register accesses. So don't use them for
> masking, whenever possible.

Philippe and Jan, thanks for the explanations.  That all makes sense.

-Jeff




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