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<p>Hi Lester and others,<br>
</p>
<div class="moz-cite-prefix">On 23.08.20 10:24, Lester Caine wrote:<br>
</div>
<blockquote type="cite"
cite="mid:f7e9b938-a496-45f6-2451-16aef2603277@lsces.uk">Many
slave devices do not rely on having a power consuming clock
actually on board and instead access a master time source on the
system, so the need for a full calendar system is avoided, but
instead the time service needs to handle DST changes and this is
where tzdist provides a documented standard to provide that area
of the service.
<br>
</blockquote>
<p><br>
</p>
<p>As this discussion has demonstrated IoT is so widely varied that
it is difficult to characterize a single set of requirements.
There are a great many environments:</p>
<ol>
<li>Consumer with an Internet connection, in which case it can use
tzdist or similar, or it will have sufficient space to store the
tz database, which itself was designed for efficiency.</li>
<li>BLE/BT/Zigbee device or similar with nothing. Here either it
slaves time or doesn't bother at all. There are power
scavenging switches that fall into this category, and certain
classes of sensors like cement dryness ones that are intended to
only work for 4-6 weeks on low power.</li>
<li>Full powered PLCs that do not have Internet access. These
will take software updates from time to time, and will vary how
much they care, depending on auditing requirements, but likely
will operate in GMT for those due to synchronization issues.<br>
</li>
<li>Low powered long-lived devices. A good example of this would
be a box car sensor on the railroad that has to go five years
without scavenging (e.g., battery), which will periodically
chirp a message. It may need synchronization with neighboring
cars, but won't use a fixed time to do it because it won't have
an RTC.</li>
</ol>
<p>A great many devices will only be updated very rarely. They do
not have Internet access and will be in inconvenient places, like
the ground in an oil field in Alaska. Some will have downtime
windows, like devices used in battle conditions. Some devices
won't be put into service for years, and when they are, they'll be
expected to function properly.</p>
<p>In all of these cases, I suspect that either TZ can accommodate
them with what's there today, or there is no standard change that
will accommodate them at all.</p>
<p>Eliot<br>
</p>
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