CCSDS AOS Deframer

[Willmac16]

Related Issue(s)
Has Unit Tests (y/n)	y
Documentation Included (y/n)	n
Generative AI was used in this contribution (y/n)	y

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Change Description

Add a CCSDS AOS SDL version 5 defamer that supports:

• Space Packet Protocol
• Encapsulation Packet Protocol
• FECF on or off
• 1 virtual channel--all the internal code should be ready for multiple just needs agreement on config & output port setup (i.e. vc per port array index)

Rationale

You need an AOS Deframer to rx AOS Frames from payloads/other craft.
AOS lets you do fixed frame width w/ variable packet size (including packets that span multiple frames)

Testing/Review Recommendations

Take a look at the processing I'm doing on SPP & EPP packets and what I'm emitting in the context for them. I could imagine a later rev of this component sharing w/ SPP defamer more logic/doing its job for it.

Other facet on the SPP & EPP processing is how light my validation is. I'm only checking that they contain the right PVN & grabbing size + idle. If we moved the full SPP parsing into this/called into a lib then you could maybe avoid throwing away packets by ID-ing a problem earlier (although dropping a frame upon packet issues is probably the only safe thing to do).

A double check on my read of the EPP spec would be beneficial since I caught a few bugs that lingered all the way into testing.

Future Work

I am likely done w/ AOS for near term; however, future work could be:

• Porting downlink stack to AOS
• Using AOS Framer to bootstrap USLP
• Making a proper EPP Framer & Deframer
• Consolidating logic into a lib btw AOS, SPP, & EPP deframers
• Writing an AOS Frame Detector if using AOS over a byte stream like tcp vs a datagram protocol like UDP

AI Usage (see policy)

• Claude Code for Web did the first pass
• The Claude Code GitHub extension addressed feedback on 3-4 commits
• Over the past couple days, while I worked in VSCode I would use ChatGPT Codex & Claude Code CLI for minor code movement/event creation and test tweaks. I've reviewed (and quite often heavily refactored) all of the flight code to match my stylistic and structural preferences

Overall, I'm not convinced the first 2 steps really provided that much of a speedup since much of the EPP structure was completely wrong, and the approach to spanning packets had significant code duplication. Maybe a minor psychological speedup simply because I had code to review to bootstrap rather than a blank slate.

The minor test writing & event creation usage felt like a speedup, but better editor skills/snippets might be able to handily beat that.

[Willmac16]

This PR should look less scary once #4630 merges

[github-advanced-security]

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