Support Vaisala Spectro Pavement Sensors

[djaeckel-wai]

Vaisala's Spectro Pavement sensors, such as the DST111 and DSC211, use an optical sensor to determine the pavement surface state, level of grip (friction), and temperature. "DST" labeled sensors are bundled with an additional atmospheric sensor, typically a HMP60, to provide air temperature, relative humidity, and dewpoint. These sensors do NOT adhere to the NTCIP specification, but rather report data within Vaisala's "enterprise" table.

This driver was originally made by Michael Darter from Iteris, Inc. on behalf of Alaska DOT&PF and WyDOT for IRISv4. I've updated it to work with IRISv5 and fixed minor bugs.

Please let me know if there are any questions or stylistic changes needed.

[DougLau]

The BER class changes make me nervous without fully understanding the purpose. What is the reason for that?

[djaeckel-wai]

In retrospect, I should have known this would come up and I should have brought it up in my initial write up. Sorry!

The change is to allow decoding huge OID numbers, but honestly, it's something Mike Darter added that I don't completely understand. I have a vague recollection that I had some problems porting some functionality to IRISv5 without that change, but I don't recall the details.

Let's put a pin in this PR!

I'll spend some time early next week to verify that it's needed for the spectro sensors AND if so, I'll provide a write up on how it works and why it's needed.

[djaeckel-wai]

The OID subId value is currently limited to 16383 and Vaisala's enterprises table ID is 16961. I've opened up issue #306 and pull request #307 to address the issue, as it's related but separate to this changeset.

I prefer my implementation of the BER OID encoding algorithm within the focused PR to what is included in this one (it's much simpler!). I need to undo the BER changes within this changeset before this is merged.