feat(kble-c2a): fragment oversized Space Packets across AOS Transfer Frames#178
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feat(kble-c2a): fragment oversized Space Packets across AOS Transfer Frames#178Kentaro Sugimoto (tarotene) wants to merge 2 commits into
Kentaro Sugimoto (tarotene) wants to merge 2 commits into
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…Frames
Per CCSDS 732.0-B-4 §4.1.4, a Space Packet (SP) may span multiple AOS
Transfer Frames via the M_PDU First Header Pointer (FHP) mechanism.
The previous implementation rejected any SP larger than the M_PDU Data
Zone (432 bytes) with an error, and also contained a latent
underflow for SP sizes in [426, 432] where the trailing Idle Packet
would become malformed.
This commit rewrites `to_aos_tfs` (renamed from `to_aos_tf`) to emit
one or more 444-byte AOS TFs per input SP:
- Case A (L <= 425): single TF, SP + Idle Packet -- behaviour preserved
byte-for-byte (asserted by a golden test).
- Case B (L > 425, L mod 432 in {0} union [1..=425]): full 432-byte SP
chunks with FHP = 0x07FF (No Header) for continuation frames;
final frame has FHP pointing to the trailing Idle Packet; when SP
ends exactly on a Data Zone boundary, a dedicated Idle-only TF
(FHP = 0) is appended.
- Case C (L mod 432 in [426..=431]): a minimum 7-byte Idle Packet is
prepended to the first frame to shift the SP start by 7 bytes, which
moves the tail remainder back into [1..=6] -- a region where the
trailing Idle Packet satisfies the CCSDS 133.0-B-1 minimum size.
frame_count advances once per emitted AOS TF (not per input SP),
which is the continuous-per-VC behaviour required by CCSDS 732.0-B-4
section 4.1.2.4.
The caller run_sp_to_aos_tf is updated to iterate over the returned
Vec<BytesMut> and send each frame individually.
Fourteen unit tests cover the full size matrix, including pathological
sizes, exact Data Zone multiples, round-trip SP reconstruction, Idle
Packet structural validity, and frame_count wrapping.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
kble-c2a spacepacket to-aos-tfpreviously assumed one Space Packet (SP) fitsentirely in one AOS Transfer Frame. This violates CCSDS 732.0-B-4 §4.1.4, which
defines the M_PDU First Header Pointer (FHP) mechanism to support SP spanning
across multiple frames. The command now implements that mechanism.
An additional latent bug is fixed simultaneously: SP sizes in the range
[426, 432] passed the explicit upper-bound check but then caused a
usizeunderflow when computing the trailing Idle Packet length, producing either a
panic (debug) or a malformed 444-byte frame with
Packet Data Length = 0xFFFF(release).
Behaviour change matrix
Each row shows the total SP length
Lagainstkble-c2a spacepacket to-aos-tf.Lusizeunderflow; release: writes 444 B frame with malformed Idle Packet (Packet Data Length = 0xFFFF, 0 data bytes)Err("Space Packet is too large: 433 bytes")ErrErrErrErrErrErrSupporting observations
frame_countnow increments once per emitted AOS TF (not per input SP), matching the continuous-per-VC requirement of CCSDS 732.0-B-4 §4.1.2.4. Single-frame cases (L ≤ 425) still increment by 1, preserving existing behaviour.L ∈ [426, 431]was a silently broken band: the release build emitted a 444-byte frame with a corrupt Idle Packet. This is repaired without changing the single-frame output forL ≤ 425.L < 7is now explicitly rejected withErr("Space Packet is too short: {L} bytes"). Previously, such input produced a TF with no valid SP content.Fragmentation algorithm
Three cases based on
Landr = L mod 432:L ≤ 425): single TF,[SP | Idle(432−L)], FHP = 0. Output preserved byte-for-byte.L > 425,r ∈ {0} ∪ [1..=425]): emit full 432-byte SP chunks (FHP = 0x07FF for continuation), then a tail frame with[SP_remainder | Idle(432−r)]at FHP =r. Whenr = 0, append a dedicated Idle-only TF (FHP = 0).r ∈ [426..=431]): a naive tail would leave fewer than 7 bytes for the Idle Packet, violating CCSDS 133.0-B-1. A minimum 7-byte Idle Packet is prepended to the first frame, shifting the SP start from offset 0 to offset 7. This moves the effective tail remainder from[426..=431]to[1..=6], restoring CCSDS compliance.Test plan
cargo test -p kble-c2a— 14 new tests pass (all 19 total, including 5 pre-existingtfsynctests)cargo clippy -p kble-c2a -- -D warnings— no warningsL ≤ 425:sp_bit_identical_to_legacyasserts byte-for-byte equality with the output of the previous implementationassert_sp_round_tripPacket Data Lengthfield) verified for all trailing and prepended Idle PacketsReferences
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