Svc::TlmPacketizer: shrink per-channel packetOffset storage from FwSignedSizeType to I16

[Mikefly123]

What

TlmPacketizer::TlmEntry stores FwSignedSizeType packetOffset[MAX_PACKETIZER_PACKETS]
per channel. The value is a byte offset into a ComBuffer-sized packet (bounded by
FW_COM_BUFFER_MAX_SIZE, typically a few hundred bytes) or the -1 "not in this
packet" sentinel -- a 64-bit signed type per slot is 4-8x oversized. Shrinks the array
to I16 (keeps the -1 sentinel; supports packet offsets to 32 KB) with a
config-time FW_ASSERT range guard retightened at the single assignment site in
setPacketList. No other changes needed: the sentinel comparisons and buffer-index
uses compile cleanly with I16 via integer promotion.

Why

On small targets this field dominates the component's footprint. Diff is 3 lines +
2 comment lines.

Validation

Measured on a real CubeSat deployment (MAX_PACKETIZER_CHANNELS=202,
MAX_PACKETIZER_PACKETS=22, RP2350/Zephyr, PROVES v5e flight board):

• -27,472 B BSS in CdhCore::tlmSend (60,480 -> 33,008 B, -45%)
• Svc/TlmPacketizer UTs: 12/12 passed (1 pre-existing skip, present in stock config too)
• HWIL-verified: clean boot, no fault/reboot over session; telemetry decodes
  bit-correct (49 distinct channels, sane values); NO_OP round-trip PASS; SEND_PKT
  PASS for Beacon and Health packets; live heap walk (sys_heap) matches the
  nm-predicted BSS delta exactly -- free-at-boot grew 11,504 -> 38,976 B (+239%),
  reclaimed BSS moved 1:1 into the malloc arena.

Base branch note

This PR targets pcr-usp-base, a branch pinned at 8a62e455a90b6d4f498c332d45d65a2a819988d8
(the v4.2.2-era commit that lib/fprime is pinned to in
proves-core-reference#439),
not devel, which has diverged significantly from that pinned commit.

Provenance

This change was not carried as a reusable branch on Mikefly123/fprime; it was
prototyped directly against 8a62e455 and applied here from the source patch
(fprime-tlmpacketizer-i16-offset.patch, see
proves-core-reference bench-diag logs) onto pcr-usp-base. Byte-equivalent by
construction (the patch applied cleanly with no fuzz).

Related

• feat: UHF radio port to Semtech USP — v5e board, UspRadio integration, carried patches (central tracking PR) proves-core-reference#439
• Propose upstream fprime fix: TlmPacketizer packetOffset is 64-bit, wastes ~27 KiB on 32-bit targets proves-core-reference#469

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 97e39638-818e-47e5-bbbb-42b0e8ec4365

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[Mikefly123]

Stack position 3/3 (top) of stack nasa#6: #1 → #2 → #3, base fix/sched-tick-drop-annotations (rebased onto #2, force-pushed). Linked via gh stack link. Stack-top tree verified byte-identical to feat/proves-usp-radio@baf163f.