[ntp:hackers] FreeBSD or die

Tim Shoppa shoppa at trailing-edge.com
Thu Dec 16 11:31:27 PST 2004


Paul wrote:
>  i suggest a 4-port self-powered (laptop style) usb hub and four
> usb/rs232 converters, which freebsd sees under the "ucom" driver.

What's the typical latency and jitter in the latency on these USB <-> RS232
converters?  How much of that latency/jitter is in the driver and how much
is in the device?  Is it conceivable to do PPS over the DCD line with one
of these, or is that just laughable?

My experience with USB<->serial converters under Windows was pretty sad,
latency was of the order of 100ms with nearly 100ms of jitter, but I
don't know how much of that to blame on Windows, how much on the Windows
driver, and how much to blame on the converter itself.  It's also
entirely possible that the blame was really on the system configurator
(me!)

Tim.




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