Re: Datum (Bancomm) GPS glitches

[Bill Cruise <cruise@cfht.hawaii.edu>]

Thanks for the replies on the GPS glitches.  I guess I didn't state
enough in the previous mail.  The Datum GPS does have a hardware
latch, which you set by reading the most significant byte first.  It
is cleared by reading the least byte last.  Data is in 8-bit bytes,
two BCD digits in a byte, plus one or two status bytes.  I have
asked Symmetricom, the successor to Datum, if there is a possibility
that the hardware register could have a problem latching, similar
to what can happen in software.

As far as my reading goes, the best suggestion so far, by Andy
Foster, is to turn off interrupts while reading.  For a very little
bit of overhead, this sounds like a very good idea.  I may also
look at Jeff Hill's suggestion of plugging into drvTS.c so that the
EPICS timestamps come from the GPS.  Right now they come from the
on-board clock, which has very poor accuracy.

Thanks everyone,

Bill



William L. Cruise                             cruise@cfht.hawaii.edu
Electronics System Supervisor                   FAX:    808 885-7288
Canada-France-Hawaii Telescope                  Voice:  808 885-3121
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