[time-nuts] time transfer over USB
herbert at 13thfloor.at
Wed May 15 00:43:28 EDT 2013
On Tue, May 14, 2013 at 08:10:38PM -0700, Peter Monta wrote:
>>> 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 -microframe.
> 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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