The root cause of the MSE is attributed to the ISOC OUT endpoint
being omitted from scheduling. This can happen either when an IN
endpoint with a 64ms service interval is pre-scheduled prior to
the ISOC OUT endpoint or when the interval of the ISOC OUT
endpoint is shorter than that of the IN endpoint.
To me this reads like the condition is
(IN ESIT >= 64ms && IN pre-scheduled before OUT) ||
(OUT ESIT < IN ESIT)
but I suspect it really is
(IN ESIT >= 64ms) &&
(IN pre-scheduled before OUT || OUT ESIT < IN ESIT)
because otherwise this workaround wouldn't really help:
ISOC OUT ESIT < INT IN ESIT is almost always true in practice.
Moving "either" later maybe makes it more clear:
This can happen when an IN endpoint with a 64ms service interval either
is pre-scheduled prior to the ISOC OUT endpoint or the interval of the
ISOC OUT endpoint is shorter than that of the IN endpoint.
This code limits interval to 32ms for Interrupt endpoints (any
speed), should it be isoc instead?
The affected transfer is ISOC. However, due to INT EP service
interval of 64ms causing the ISO EP to be skipped, the WA is to
reduce the INT EP service to be less than 64ms (32ms).
What if there is an ISOC IN endpoint with 64ms ESIT? I haven't yet seen
such a slow isoc endpoint, but I think they are allowed by the spec.
Your changelog suggests any periodic IN endpoint can trigger this bug.
I'm not completely sure about this corner case if HS OUT endpoints can inadvertently get affected when co-existing with long-interval LS/FS IN endpoints. Our IP vendor confirmed that LS/FS devices are not affected.Are Full-/Low-speed devices really also affected?No, Full-/Low-speed devices are not affected.
The interesting question here is whether LS/FS devices with long
interval IN endpoints can disrupt a HS OUT endpoint or not, because
the patch solves the problem from the IN endpoint's side.
(I assume that SS probably has no effect on HS schedule.)
Regards,
Michal