[Nut-upsdev] Documenting the NUT driver-qualification process

Ted Mittelstaedt tedm at mittelstaedt.us
Sun Jul 27 07:13:41 UTC 2014

On 7/26/2014 12:18 PM, Arnaud Quette wrote:
> Hi Eric,
> sorry for the lag, summer time...
> I'm first seconding Charles comments
> 2014-07-09 12:31 GMT+02:00 Eric S. Raymond <esr at thyrsus.com
> <mailto:esr at thyrsus.com>>:
>     I think the time for me to get involved in NUT documentation has come
>     again.
> welcome back
>     Late last week I had to buy a UPS under time pressure.  The Eaton unit
>     that thus project gifted me with in 2006(?) died during a severe
>     thunderstorm watch, so it was off to MicroCenter to get a replacement
>     pronto.
>     I wound up buying an APC BN700MC.  It was what they had in the
>     performance range I needed.  The removable battery door was pleasing.

>     Based on the experience, I have updated the UPS HOWTO:
>     http://www.catb.org/esr/ldp/UPS-HOWTO.html
>     The bad news, however, is that (a) this is not a NUT-supported device,
> I've logged an entry for the APC Modbus:
> https://github.com/networkupstools/nut/issues/139
>     and (b) the (poorly documented) NUT process for discovering and
>     customizing a driver failed at the first step.  Running upsstart
>     gave a driver fail message containing no clues as to how to recover.
> yup, definitely room for enhancement!
> I've got some ideas, beside from the obvious need to improve the
> documentation, that I'll like to discuss.
>     This is definitely USB and probably a fairly generic hidups device.
>     There is no good reason for customizing a driver profile to be
>     so difficult.
> well, I'm unsure since I'm just opening this "APC Modbus Pandora box"
> but if I understand correctly, your new unit is a microlink one.


HIS UPS is a BackUPS not a SmartUPS.  Originally the APC BackUPS DID NOT
SUPPORT any Smart protocol (the original UPSLink protocol)

But over the years it's been observed that APC has somewhat "fudged" on
the BackUPS UPSes.  Newer ones did appear to implement the UPSlink 
protocol over USB.

Microlink protocol is officially only for APC SmartUPSes.  Officially,
what your supposed to get with a BackUPS is dumb signalling only.  But,
with the newer BackUPSes that have USB output, some seemed to act like
SmartUPSes even though they were not.

APC has very much blurred the line on the model BN UPSes.  These are the
APC UPSes that look like an oversized power strip.  That's the one that 
he has.  They seem to have dropped monitoring ports completely on these 
UPSes that are under 700VA in size.  They used to make monitoring ports
on these UPSes all the way down to 350VA.  But the current models, only 
the 700VA unit like the one he bought, still support the monitoring 
port.  That port is the special wide RJ45 that has 10 conductors not 8.
It is selectable between serial and USB depending on what cable is used
with it.

> though the serial version should be Modbus only,

There is no "serial only" APC UPS that supports Modbus, in fact no APC 
smart UPS since the Microlink protocol was implemented has been "serial 
only", all have been dual-use  Serial and USB.

> I can't say at first if
> the USB ones implement if full Modbus over HID or any other mean.
> I would need traces to give more info.

The BackUPSes with USB ports might implement full UPSlink over HID.

Or they might implement Microlink over HID

Or they might implement nothing like either of that.

But they definitely don't implement Modbus.

It is best I think to refer to BackUPS and SmartUPS in the 
documentation.  Please do not refer to APC UPSes in a generic fashion. 
And please don't assume that any APC BackUPS implements any particular
protocol over USB or Serial unless you have directly tested it.  APC
BackUPS upses are the "cheap, poor relations" and are for consumers and
penny-pinching businesses that are too cheap to spend a couple hundred 
bucks on decent gear.  Purchasers who want full functionality should be
encouraged to buy an APC SmartUPS.


> anyway, this may not be as generic USB as you think.
>     What I'd like to do is this: confer in real-time, perhaps via IRC,
>     with someone who knows this process.  Ask about every step (thought
>     processes and diagnostics).  *Write them down* and turn this into a
>     document on how to qualify and support a new device.
>     Volunteer, please?
> I am
> I would also be more than happy to have you looking more closely at NUT
> documentation in general [1].
> Charles and myself have worked a lot on the Asciidoc conversion, with
> some improvements.
> But I know it needs an overall revamp, with usability in mind.
> Would you be willing to work on that one?
> cheers,
> Arno
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