[Nut-upsdev] MGE NMC and NutShutdownModule (and other stuff)

[Arjen de Korte]

Citeren Marco Chiappero <marco op absence.it>:

>> Yes, that's what I'm intending to do (and what I have already done  
>> for a large part already by the way). This will reduce the latency  
>> for changes in the power state to essentially zero. At the same  
>> time, we can increase the pollinterval to something like 60+  
>> seconds or so. Receiving an alarm will then trigger a poll of the  
>> summary and/or get_object pages, to get all available data.
> What about including these ideas and functions into the netxml-ups  
> driver maintaining the backward compatibility

This is what I'm doing now.

> We can create a single subscription connection, from which we only  
> need to read the BelowRemainingCapacityLimit flag (to allow the use  
> of the testing button) and the DelayBeforeShutdown value (about the  
> outlet used by the system). An alarm message reception can then  
> trigger a summary page scan (no need to set timings) while the  
> get_object page, with extended data, can be read every  
> "pollinterval" (the user can choose whether to have it low and  
> stress the NMC or not).

Something along these lines, yes.

> We can also lower the summary page scans, reading more data from the  
> alarms, for example:
> - alarm level == 1 -> update data using this alarm and read the  
> summary page every "pollinterval"
> - alarm level == 2 -> read the summary page immediately
> Does it sound reasonable?

Yes. Although it is questionable whether it makes sense to handle  
different alarm levels. When polling for the summary and/or get_object  
pages, you'll already get all data, so we might even skip the alarm  
processing all together without losing any data. The best thing about  
the subscription mode is that it will alert us if something is  
happening. This means that we can increase the time between normal  
polls, but do additional polls when an alarm arrives.

> Moreover reading the summary page we also know when to start the  
> shutdown procedure on every outlet, so we have every kind of  
> information we need/want, with just a single subscription.

Indeed. So it wouldn't be a problem that only one NSM client can run  
on the host where the upsd server lives. As long as we make sure that  
only one is connected to any NMC at the same time. Otherwise, you'd  
get an endless mess of reconnects... :-)

Best regards, Arjen
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