[Nut-upsdev] Re: Serial Ports (Was Re: Common Power Management : NUT and HAL (stage 1))

[Arjen de Korte]

>> Also: we certainly can't run serial PNP probing automatically, only in
>> response to a user choice of deciding to probe for serial ports. I say
>> this because maybe it will crash some old devices or some that don't
>> support Serial PNP. This is correct, yes?
> Yes..

Maybe not. I think most (if not all) serial devices won't be harmed by
changing the control lines (this problem is also pointed out in the serial
PnP specification in Annex B). On the other hand, we need to be absolutely
sure about this (or make it configurable), so at the moment I tend to
agree not to do this automatically until we are.

> An APC BackUPS (or SmartUPS with a grey dumb cable) will power it's load
> off if RTS is held high for a second (I think).

I've had the fortune of experimenting with this configuration a few months
ago and it poses no problems with the serial_probe program Arnaud directed
me to a while ago (can't remember where he found it). The specification of
the serial PnP protocol says you'll need to keep this line high for 200ms
(if memory serves) which is not nearly long enough for the UPS to shutdown
the load. The BackUPS Pro 650 will happily report its serial PnP string.

Since the serial PnP protocol is fairly old already (first draft more than
13 years ago) I think many (if not all) serial devices designed for the
consumer market will at least tolerate it (serial PnP was standard from
Windows 95 onwards if I remember correctly).

Regards,
Arjen
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