Fix universe buffer for ArtNet

[Joebayld]

This should be a UInt8 buffer, not an Int16. Previously setting a universe in the options did nothing.

[wiedi]

I'm not sure this is correct. I currently don't have any art-net devices to test, so I'm just looking at http://artisticlicence.com/WebSiteMaster/User%20Guides/art-net.pdf.

The two relevant fields seem to be:

• 7, SubUni - low byte of the 15 bit Port-Address
• 8, Net - top 7 bits of the 15 bit Port-Address

And Port-Address is defined as

one of the 32,768 possible addresses to which a DMX frame can be directed. The Port-Address is a 15 bit number composed of Net+Sub-Net+Universe.

Where

• bit 15: zero
• bits 14-8: net
• bits 7-4: sub-net
• bits 3-0: universe

Currently the assumption is that the "universe" passed in as an option is the full "port-address". Maybe this option should be renamed to "port_address" or there should be additional options for the "net" and "sub-net"?

The other actual thing that seems wrong is that writeInt16BE should probably be writeInt16LE - maybe you can test if this also works with your hardware as I'd think that to be a better fix.

Thanks!

[Joebayld]

I just tested - writeInt16LE fixes it. I typically use a UInt8 and ignore the other buffer as you would never need to go over 255 universes. But you're correct. The endians were just swapped.

Thanks

[Fensterbank]

@Joebayld If this fixed the problem, do you want to update your commit to just change writeInt16BE into writeInt16LE? Then we could merge and close this pull request.

Thanks!