[time-nuts] Pendulum CNT91 with TimeLab

[John Miles]

Good to hear the modified driver helped -- thanks for the confirmation!
I'll leave that option in the code for future releases.

There's no compelling reason to use the generic talk-only driver with a
counter that is also supported by a native talk/listen driver, as long as
the latter works reliably.  The native drivers don't do much to configure
the counter, but they can do one or two helpful things such as ensuring that
certain statistical features that would interfere with the measurement are
turned off.  They also allow the counter to reside on a GPIB segment that's
shared with other addressable devices, which is problematic in talk-only
mode.

The trouble with the native drivers arises from the fact that the only TIC I
have around here is the HP 5370B, which doesn't use the same driver code as
the SCPI-era models like the 5313xA, SR620, DTS207x, etc.   So when I make a
change that affects those drivers, it's always going to be a "Customer as
Beta Tester" scenario.  And we all know how well untested code usually
works.

The need to support Prologix USB, Prologix Ethernet, and NI 488.2 adapters
complicates matters further because their low-level behavior, timing
characteristics, and driver interfaces couldn't be more different from each
other.  Add in the notion of counters like the Pendulum that are
almost-but-not-quite compatible with supported models, and the fact that
even the native TimeLab drivers still rely on the user to set up the
measurement parameters, and you get a pretty intimidating matrix of
conditions that are realistically never going to get tested until someone
tries to use them. 

The talk-only driver simplifies the picture because I can test it with the
5370B just by flipping a DIP switch and verifying that it works with the
three supported GPIB adapter types.  It doesn't rely on issuing
device-specific trigger and read commands to counters I don't own.
Talk-only measurements are still not 100% reliable due to occasional
weirdnesses in the GPIB adapter or counter firmware, but those aren't my
fault. :)

Basically, just use whichever driver works most reliably in your particular
situation, and keep the reports coming so we all know what works and what
doesn't. 

-- john, KE5FX
Miles Design LLC 


> Hi John
> 
> Just as a quick follow up, I'm still intrigued as to why I've been
> seemingly unable to get the CNT91/FCA3100 to run in talk-only mode and
> might  well
> come back to that when I have a bit more time but, from a TimeLab point of
> view, with the HP emulation up and running would there actually be
> anything
> to be gained by doing so?
> 
> Regards
> 
> Nigel
> GM8PZR