[time-nuts] GPS USB dongle for time server
michael.conlen at ncf.edu
Tue Nov 9 04:26:36 UTC 2010
On Nov 8, 2010, at 10:58 PM, jimlux wrote:
> jim s wrote:
>> This is probably the thousandth time this was asked, but I googled and didn't get a direct answer.
>> I want to do a crude (as in to the second or so) time server inhouse to add into a group of high accuracy servers. This is so that I can go off grid and still get updates.
>> I see that there is a way to get a feed called PPS or with PPS via RS232. The discussions of using USB instead are concerned with having too much jitter.
>> since USB by its nature won't have an accurate exact dedicated line to let the GPS toggle to do a time hack to the software, I can see why RS232 is preferable with the hardware signal lines they have.
>> If I just go with the NEMA stream as it gets to me via an USB HID Com port, I assume that there will be some jitter baring a way to send in the physical time hack.
> I would think that USB is not inherently worse than a hardware RS232. Both have some interrupt latency, but it's small in both cases. USB has to handle audio reliably at no worse than 8kHz sampling rate.
And as an audio nut as well as a time nut I can say that USB and Firewire both do this poorly (under certain conditions).
I often have to restart encodings of multi-track audio if I don't shut absolutely everything down on what should be a well powered system because USB and Firewire both are unable to keep up.
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