Bruce Simpson <bms@fastmail.net>:
On 13/05/16 20:39, Eric S. Raymond wrote:
In 2012, nearly three years before being recruited for NTPsec, I solved this problem as part of my work on GPSD. The key to this solution is an obscure feature of USB, and a one-wire patch to the bog-standard design for generic USB that exploits it. Technical details on request, but what it comes down to is that with this one weird trick(!) you can mass-produce primary time sources with a jitter bounded by the USB polling interval for about $20 a pop.
The USB 1 polling interval is 1ms.
What about USB 3.1 (assuming the device is not intended to be backwards compatible with the polling model) ? I should point out Intel intend to retire EHCI/UHCI and implement only xHCI.
Nobody makes GPSes with even USB 2 or 3 yet, and it is unlikely to happen for a long time. Cost reasons - USB GPSes are cheap consumer-grade hardware and the manufacturers care about fractions of a cent on the BOM. -- <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>