[chirp_devel] DTR/RTS control

[Dan Smith]

> As I noted in the feature request, some cables want both DTR and RTS
> on, and use ground for the voltage reference base.  Others want RTS
> low and DTR high, and some want the reverse.

From my experience, only larger CI-V (, etc) converter boxes are
dependent on RTS being high to power the circuit. I've seen no reports
of issues with any cable on any typical VHF/UHF type setup, so I don't
believe this to be a problem for those types of radios (which, of
course, are the major target market for CHIRP). Further, I believe it
is the overwhelming common practice (rightly so, IMHO) for a opened
serial port to assert DTR unless configured to do otherwise. I believe
that is likely the reason why we've seen no reports of this being a
problem until now. At least on all my systems, CHIRP opening the port
asserts DTR, which powers my MAX232-based custom interface cables.

I'm hesitant to expose such a setting in the UI without any indication
of need or issues in the field because it becomes one more thing that
can be set incorrectly by the user and thus one more thing that we must
clarify, explain, etc in order to provide support.

The other important thing to note, of course, is that probably more than
90% of CHIRP's users are utilizing cables with inbuilt USB interfaces,
which are always powered from the bus and for which DTR and RTS
settings (for the purposes of powering a converter) are meaningless. We
have no reasonable way of determining if a device selected by the user
fits into this classification, which means exposing them in the UI
provides only confusion, IMHO.

What commercially-available cables require RTS low and DTR high?

Since I'm quite certain this is only a problem with HF CI-V-like
interface boxes, if anything, I'd like to restrict such a setting (if
we were to add it) to those drivers that are likely to have such a
requirement.

I'm not really sure what my preferred path forward would be. Perhaps a
documented, but low-visibility config file option that would let
someone enable it for a specific need? Again, with no reports of issues
with this, I'm hesitant to expose it widely.

-- 
Dan Smith
www.danplanet.com
KK7DS
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