[time-nuts] time transfer over USB
pmonta at gmail.com
Tue May 14 23:10:38 EDT 2013
> > Bulk transfer might work well on a system where nothing else is going
> > so "best effort" translates to "now".
> Does it mean "now" or "next polling cycle"?
It means "now", or pretty close. No waiting for start-of-USB-frame or
Herbert mentions that all USB transfers are host-initiated, which is true
(even for the so-called "interrupt" transfers), but the latency is usually
much less than one frame on a lightly loaded bus I believe.
I agree with Magnus' remark that this is not rocket science. Maybe it's
time for a small proof of principle, using something like a Teensy board,
that takes PPS edges from the outside world and connects them to USB.
GNSS samplers should be timestamping their packets so that the relationship
between sample number and device-local time (and ultimately also host time)
can be known.
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