[jeff_marshall]

I've got a customer that wants to get access to the PTP[1] registers of a NIC from user space. The customer suggests that context switches introduce too much latency and indeterminism (pre systems integration phase - lots of software from different teams ends up running on the final platform) to introduce a reference monitor (capability-based microkernel or otherwise) given known techniques on modern hardware. I'm afraid I can't share the specifics because I don't have them, but I trust the source.

I will grant that this case is an outlier, but this customer use-case is real enough to drive development dollars. It may not be the norm, but precision timing access appears to be very useful in some hard real-time contexts given current hw/sw realities.

[1] https://en.wikipedia.org/wiki/Precision_Time_Protocol

[naasking]

Wouldn't this involve modifying the driver then?

[jeff_marshall]

Yes, as well as some lower-level software. (sharing portions of a PCI BAR region isn't trivial in a hypervisor, when multiple guests are involved).

Mixing safety criticality levels is hard.