Mailinglist Archive: opensuse (882 mails)

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Re: [opensuse] Serial to USB adaptor
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Fri, 03 Dec 2010 15:20:15 +0100
  • Message-id: <1291386015.27828.16.camel@xxxxxxxxxxxx>
On Fri, 2010-12-03 at 09:01 -0500, Brian K. White wrote:

Interesting problem. I love how it exemplifies how "progress often isn't".

Maybe get a head start by licensing a reduced version of this that only
has to keep two nodes in sync, the pc and the gps.

Only keep two things in sync... That's no fun. We are also syncing
images from firewire/Gig<E>Vision/JPEG2000/v4l2 cameras, vehicle
movement from linear pulse transducers, an assortment of lasers,
accelerometers, inclinometers, gyroscopes, and other devices I am surely
forgetting. Oh, and of course operator input in all this. That one is
the nastiest one to deal with in X11 systems (who's concept of time is
relative to when the X server started - not the systems' clock).

This sounds interesting. But I wonder how this really works when USB is
a packet-based system on which all devices must share access. I suspect
this is a sort of fast hub that accepts packets from each connected
device immediately and then time tags each packet from the devices as
they pass through, allowing you to check this encapsulated info on the
host via a driver that can peel off the time wrapper. As long as you can
assume there is no delay getting it in to this hub, I guess this could
improve time tagging. I will bookmark this one.

It's the only thing I find at all when I google for variations of
synchronous, deterministic, high precision, timing, and usb.

I would have thought every dinky usb sound card would need good timing,
and usb modems that expect to fax reliably. But then again, my
incredulity doesn't matter because current bluetooth A2DP audio devices
continue to have have wow (speed skew, as in "wow & flutter" like
records and tapes had, but no flutter) no matter how incredulous I am
about it. I mean, CD's had no wow since 1982, laserdiscs had no wow
since 1978. Why in 2010 do several different smart phones (different
OS's different manufacturers, used with different receivers both in car
and in home) have wow when playing audio over bluetooth?

Progress often isn't.

Still, USB has generally made connecting many types of peripherals much
easier. I have no trouble with it for many uses. My new laptop has USB3,
but I have no devices to test with. I wonder what a 10x speed
improvement will really mean. Probably that all devices will get more
verbose, and just fill the capacity with, effectively, the same content.
I'm showing the telltale sings of age here...

Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696

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