Add ALDL link-layer type

[jakem72360]

PR to match #1143.

Added link-layer type 297 for GM ALDL as described here: Holden - ALDL (8192 Baud)

[guyharris]

You should probably link to https://holden.asger.xyz/wiki/Holden:ALDL_(8192_Baud) in the page for LINKTYPE_ALDL, to describe at least some of the ALDL payload.

[guyharris]

And if it's different in the 160 baud link and the 8192 baud link, should this be LINKTYPE_ALDL_8192_BAUD?

[guyharris]

And, as the Wikipedia page for ALDL indicates, how model-dependent is the format?

[jakem72360]

And, as the Wikipedia page for ALDL indicates, how model-dependent is the format?

Documentation is scarce, but the majority of ALDL devices that operate at 8192 baud has a consistent frame format of <id> <len> <data+n> <checksum>.

I considered creating LINKTYPE_ALDL8192 instead, but since it's the most common, I figured LINKTYPE_ALDL with a possibly separate LINKTYPE_ALDL160 would be more appropriate in future.

[jakem72360]

I can change the definition to LINKTYPE_ALDL_8192_BAUD if that would be more clear.

As for the site link, the site itself is a WIP, and the domain isn't finalized. Hence why I was hesitant to include it in long-term documentation at this stage.

[guyharris]

Documentation is scarce, but the majority of ALDL devices that operate at 8192 baud has a consistent frame format of <id> <len> <data+n> <checksum>.

...but is <data> model-dependent (so that dissecting anything more than <id>, <len>, and <checksum> would require some other mechanism to specify the model)?

[jakem72360]

Documentation is scarce, but the majority of ALDL devices that operate at 8192 baud has a consistent frame format of <id> <len> <data+n> <checksum>.

...but is <data> model-dependent (so that dissecting anything more than <id>, <len>, and <checksum> would require some other mechanism to specify the model)?

It is, but I'd argue that transcends the link layer. Detecting the vehicle model can be done with relatively straightforward heuristics. The purpose of my pull request, is to allow captured ALDL frames to be passed between programs. Anything outside of the message ID, length and checksum are beyond the link-layer, and is the responsibility of a program/user to interpret the meaning of the data section.

[guyharris]

This needs to be updated, as 297, 298, and 299 have been assigned to other link-layer types.