Issue writing to LAVs

[michael-senva]

I'm having some trouble writing to an LAV. I am able to read out a value correctly but get hit with an 'Invalid Constructor Datatype' error when attempting to write the value back.

Here's a snippet to illustrate what I mean:

import BAC0
network = BAC0.connect()
network.read('X.X.X.X largeAnalogValue 1 presentValue')
>>> 0.0
network.write('X.X.X.X largeAnalogValue 1 presentValue 0.0 - 1')
>>> Error (Invalid Constructor Datatype)

I've dug through the library/docs, and it looks like it's expecting the Double object type where the error is raised.

Am I querying correctly? Any recommendations on getting it working?

I've read a bit about creating custom constructors but hit a wall with getting that working. Any help or direction is appreciated! :)

[bbartling]

i dont think i have ever heard of a LAV? Large Analog Value? Is that in the BACnet spec?

[michael-senva]

Large Analog Value, that's correct. It's effectively BACnet's Double type. BAC0 doesn't have trouble with reads, but it doesn't appear to detect a written double and throws an incorrect data type error. I've tried a variety of permutations without success.

It looks like bacpypes supports the Double type under the hood, so the solution may just be creating a new class to handle it (similar to this one for writing text with spaces), but no success so far- I don't have much experience in how Python class structures work, so it may be a fairly straightforward fix I'm just not seeing.

[bbartling]

Gosh interesting, i have yet to run across a Large Analog Value in the wild.

What does your code look like so far? I am fairly handy in bacpypes too.