In message 20090518041523.7b7cdb...@ip-64-139-1-69.sjc.megapath.net, Hal Murr
ay writes:
Why not add a hardware latch with a fixed delay to read.
Because then you need locking to prevent multiple threads/processes
from accssing the hardware at the same time.
--
Poul-Henning Kamp | UNIX
M. Warner Losh skrev:
: I think this case doesn't work right:
: read high
: overflow
: long gap
: read low
: read high
:
: Suppose the low half overflows once a second so I can use handy numbers.
:
: If the long gap is 0.6 second, the MSB of the low half will be on so we use
: the
Hal Murray skrev:
I'm interested in the case where interrupts and scheduling are
enabled so there may be arbitrary gaps inserted into the simple
code.
Interrupts enabled means that you can't make it reliable.
Sure you can. Just compare the two high samples and try again if they are
stanley_reyno...@yahoo.com said:
I need to go back and read what you are trying to measure with your
clock. Is it internal to the computer or an external event ?
I was thinking of a FPGA on a PCI bus. It has to be PCI rather than USB in
order to get reasonable timings.
I was going to put
In message 20090518081256.97f2bb...@ip-64-139-1-69.sjc.megapath.net, Hal Murr
ay writes:
I was going to put the Unix clock in the FPGA. It's a pair of 32 bit words.
The high word is seconds since some magic date/time. The low word is
nano-seconds within this second.
Please, will you guys
On 5/18/09 1:12 AM, Hal Murray hmur...@megapathdsl.net wrote:
stanley_reyno...@yahoo.com said:
I need to go back and read what you are trying to measure with your
clock. Is it internal to the computer or an external event ?
I was thinking of a FPGA on a PCI bus. It has to be PCI
On 5/18/09 6:18 AM, Lux, James P james.p@jpl.nasa.gov wrote:
On 5/18/09 1:12 AM, Hal Murray hmur...@megapathdsl.net wrote:
stanley_reyno...@yahoo.com said:
I need to go back and read what you are trying to measure with your
clock. Is it internal to the computer or an
In message c636b079.7d49%james.p@jpl.nasa.gov, Lux, James P writes:
An integer divide in software is quite fast
(unless you're working with something like a Z80).
You only need to divide when you want to change your estimate of the
counters range, for generating timestamps a multiplication
In message: c636b079.7d49%james.p@jpl.nasa.gov
Lux, James P james.p@jpl.nasa.gov writes:
: I also wouldn't have the low order counter count nanoseconds, or even set it
: up as seconds/subseconds.
I'd echo this, since you are artificially limiting the clocks that are
input to
Geoff,
I'm not in a position to check at present, but have also noticed
discrepancies in the time pips in the past. I'd not use a GPS receiver
for this, as they can easily indicate a second or so out. I use a GPS
Disciplined Receiver (HP Z3801A or Trimble NTGS50AA) for the job.
I suggest you talk
Hal Murray wrote:
One case was a gross software bug. I think it was triggered by a pending
leap second.
http://www.megapathdsl.net/~hmurray/ntp/leap-gps.gif
Interesting that the three receivers with issues were all SiRF III based. Do
you know what firmware these were running?
How are
http://petelancashire.com/gallery/main.php?g2_itemId=3279
comments on .. now in a pile that may become scrap
location is 45 miles from Portland Oregon
-pete
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li...@philpem.me.uk said:
Interesting that the three receivers with issues were all SiRF III
based. Do you know what firmware these were running?
Nope. If you know the recipe to find out, I'll ask them. :)
I just scanned their NMEA documentation and didn't see any way to get it.
How
Hal Murray wrote:
Interesting that the three receivers with issues were all SiRF III
based. Do you know what firmware these were running?
Nope. If you know the recipe to find out, I'll ask them. :)
I just scanned their NMEA documentation and didn't see any way to get it.
If memory
li...@philpem.me.uk said:
Interesting that the three receivers with issues were all SiRF III
based. Do you know what firmware these were running?
Nope. If you know the recipe to find out, I'll ask them. :)
Failing that, the sirfmon app that comes with gpsd might get the
receiver
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