PCI UDD Questions

Jan Kiszka jan.kiszka at siemens.com
Wed Mar 6 18:38:47 CET 2019


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.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux



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