[LEAPSECS] Embedded software

[Michael Spacefalcon]

Warner Losh <imp at bsdimp.com> wrote:


> Also, these systems were not on the internet, so downloading one of the many

> sources of TAI-UTC differences wasn't an option.


OK, obviously asking every system to be connected to the Internet
would be a non-starter, for security etc reasons, but what's wrong
with dedicated, special-purpose narrowband non-Internet channels?  Why
not have an old-fashioned modem (as in 9600 baud or slower) dial a
service such as ACTS that would provide the necessary Earth Correction
information?  (I realize that ACTS in its present form does not
provide this information - I'm referring to a hypothetical ACTS-like
service here.)

There is a huge difference in terms of security etc exposure between a
full-blown general purpose TCP/IP stack connected to the public
Internet and a special-purpose low baud rate serial line.  If you have
a serial port in your system, and the only piece of code that touches
this serial port (and even knows about its existence) is the single-
purpose code that retrieves Earth Correction information, expecting
just one specific (hard-coded) data format and accepting nothing else,
where is the risk?


> We had a requirement that cold spares had to sit on the shelf for up to 5

> years, and come up in a new system with the correct UTC time within 3 minutes

> of power being applied.


It seems to me that the correct solution to a problem like this one is
that whoever came up with such an unreasonable requirement should be
removed from office, and replaced with someone who would be more
reasonable.  Why was this solution not considered?

In other words, was there any true, genuine justification for the
"requirement" you have stated, other than someone's whimsical say-so?
Why did it have to produce "UTC" time, and not something like TAI or
GPS?  UTC should be for displaying *civil* times only, i.e., a user
interface or presentation issue, with all internal things done on a
timescale like TAI instead.  And if the correct *civil* time is only
for the convenience of human operators, why is it so critical to get
it right within 3 minutes of powering up a cold spare?  Surely the
world won't come to an end because of some LCD on some control panel
showing the wrong time for 25 min instead of 3 min after a technician
swapped out a module.

VLR,
SF