[time-nuts] FreeBSD, NetBSD, or Minix-III?
Lux, James P
james.p.lux at jpl.nasa.gov
Sun May 24 16:17:23 UTC 2009
On 5/24/09 8:32 AM, "Bob Paddock" <bob.paddock at gmail.com> wrote:
>> A 33.31 format would buy us a century, still allow us to get
>> nanoseconds right, but it be computationally inconvenient and
>> looks messy, so people balk at it.
>
> Anything wrong with TAI64NA?
>
> http://cr.yp.to/libtai.html
>
> "libtai is a library for storing and manipulating dates and times.
>
> libtai supports two time scales: (1) TAI64, covering a few hundred
> billion years with 1-second precision; (2) TAI64NA, covering the same
> period with 1-attosecond precision. Both scales are defined in terms
> of TAI, the current international real time standard. "
>
> TAI64NA in FPGA?
>
Of course...buried in the install notes
"But keep in mind that this is a very early release. Some of
the code hasn't been tested at all! "
As of 1998...
It also breaks the time up into seconds, nanoseconds, and attoseconds, as
separate chunks, so math isn't trivial
struct taia {
struct tai sec;
unsigned long nano; /* 0...999999999 */
unsigned long atto; /* 0...999999999 */
} ;
I don't think this library buys you a whole lot (other than useful routines
to do things like calculate easter or leap days/seconds), but at the basic
"how does one keep time" level, not particularly an improvement.
Also, someone I was discussing this with at work reminded me of a common
problem. We often run tests in a testbed where we need to have the entire
testbed running at some time *not the actual time*.. E.g. If you're
simulating a Mars entry,descent,landing scenario, you want the spacecraft
running with "time" at the expected EDL time. But, you want to have
everybody sync'd to a common source.
So, it's easy to get all the computers controlling the test gear sync'd to
UTC or TAI using something like NTP, but you need a way to have precision
"simulated time" as well.
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