[time-nuts] FreeBSD, NetBSD, or Minix-III?

[Lux, James P]

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.