F3: Selectable stream-carrier rate (Legacy / HT-MCS / VHT)#90
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The two stream demos (StreamDuplexDemo, StreamTxDemo) hard-coded a 13-byte 6-Mbps legacy-OFDM radiotap header. With the precoder stream link's FEC layers landed (#86 RaptorQ, #87 RLC), the carrier rate is now a useful robustness-vs-throughput knob. This v1 ships legacy-OFDM rate switching only: DEVOURER_STREAM_RATE=6M|9M|12M|18M|24M|36M|48M|54M (default 6M) DEVOURER_STREAM_RATE=12|18|24|36|48|72|96|108 (500 kbps units) Higher-rate HT-MCS / VHT paths deliberately stay out of this PR — they need a non-13-byte radiotap and would switch send_packet onto its VHT branch via the existing `radiotap_length != 0x0d` heuristic. F1 (#88) unlocks the HT-MCS path; a follow-up can extend RadiotapBuilder to emit HT and VHT headers behind the same env var. - New src/RadiotapBuilder.{h,cpp}: small helper exposing build_legacy_radiotap(rate_500kbps) -> std::array<uint8_t, 13> parse_stream_rate_env() -> uint8_t - Wired into StreamDuplexDemo and StreamTxDemo, replacing each binary's private kRadiotapLegacy6M[13] constant. The on-air length stays at 13 bytes so send_packet keeps these on the legacy path. - PrecoderDemo is intentionally NOT touched — its PoC plan locks the carrier to 6M. Defaults are unchanged on every code path, so the existing regression matrix and tools/precoder/precoder_stream_roundtrip.py stay byte-identical without setting the new env var. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Replaces the legacy-only v1 API with a single StreamRateCfg / build_stream_radiotap
pair that emits three radiotap variants under the same DEVOURER_STREAM_RATE
env var:
Legacy: 6M | 9M | 12M | 18M | 24M | 36M | 48M | 54M (13-byte radiotap)
HT: MCS0 .. MCS31 (13-byte radiotap)
VHT: VHT1SS_MCS0 .. VHT4SS_MCS9 (22-byte radiotap)
Plus DEVOURER_STREAM_BW (20|40|80|160), _SGI, _LDPC, _STBC.
Wire-format facts the chip-side send_packet (RtlJaguarDevice.cpp:42) relies
on:
- radiotap_length == 13 -> vht=false, rate_id=8 (legacy or HT path)
- radiotap_length > 13 -> vht=true, rate_id=9 (VHT path)
- the iterator parses *all* fields regardless of vht — so a 13-byte
HT-MCS radiotap (presence = MCS|TX_FLAGS, no RATE) is correctly
parsed via the IEEE80211_RADIOTAP_MCS case and stays on rate_id=8.
Verified against txdemo/main.cpp's own 13-byte HT beacon_frame[].
HT-MCS requires DEVOURER_TX_HT_MCS=1 (F1 gate in send_packet) to actually
fly at the requested rate; parse_stream_rate_env() emits a stderr warning
when an HT rate is parsed without that gate so users don't silently fall
back to 1M CCK. VHT has no such gate — send_packet's VHT branch
unconditionally honours the VHT info field.
Builders mirror exact field layouts already in use:
- HT 13-byte MCS layout cross-checked against txdemo/main.cpp's
beacon_frame[] (line 300) — same it_present, same MCS field positions
- VHT 22-byte layout cross-checked against txdemo/main.cpp's
DEVOURER_TX_VHT path (lines 374-409) — same known mask, same flag
bits, same coding/mcs_nss positions
Default behaviour (env var unset) is unchanged: 6M legacy OFDM,
bit-identical to the historic kRadiotapLegacy6M[13] constant.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
josephnef
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Summary
Replaces the hard-coded 13-byte 6-Mbps legacy-OFDM radiotap header in
StreamDuplexDemoandStreamTxDemowith aDEVOURER_STREAM_RATE-controlled builder that emits Legacy / HT-MCS / VHT carriers under one env var.Env var grammar
Default (env var unset) = 6M legacy, bit-identical to the historic
kRadiotapLegacy6M[13].Wire-format facts the chip relies on
send_packet(RtlJaguarDevice.cpp:42):The radiotap iterator parses all fields regardless of
vht— so a 13-byte HT-MCS radiotap (it_present = MCS \| TX_FLAGS, no RATE) is correctly parsed via theIEEE80211_RADIOTAP_MCScase and stays on the HT path. Cross-checked againsttxdemo/main.cpp's own 13-byte HT beacon_frame[] layout (line 300).VHT uses the same 22-byte layout as
txdemo/main.cpp'sDEVOURER_TX_VHT=1path (lines 374-409):it_present = VHT \| TX_FLAGS,known = STBC \| GI \| BW, MCS/NSS in user-0 nibbles.F1 dependency for HT mode
HT-MCS in
send_packetis gated byDEVOURER_TX_HT_MCS=1(F1, PR #88, merged).parse_stream_rate_env()emits a stderr warning if an HT rate is parsed without that gate so users don't silently fall back to 1M CCK:VHT has no such gate —
send_packet's VHT branch always honours the VHT info field.Hardware verification (8/8 PASS)
TX = RTL8812AU (0bda:8812), RX = TP-Link RTL8821AU (2357:0120,
DEVOURER_VID=0x2357 DEVOURER_PID=0x0120). ~200 stream frames per case, RX-side<devourer-stream>rate=Nindex parsed.STREAM_RATE=6MSTREAM_RATE=24MSTREAM_RATE=54MSTREAM_RATE=MCS5 TX_HT_MCS=1STREAM_RATE=VHT1SS_MCS3 STREAM_BW=20STREAM_RATE=VHT1SS_MCS3 STREAM_BW=20STREAM_RATE=VHT1SS_MCS7 STREAM_BW=80Every case: 100 % of received frames carry the expected rate index. Default behaviour (no env var) is byte-identical to master.
What ships
src/RadiotapBuilder.{h,cpp}—StreamRateCfgstruct +build_stream_radiotap(cfg) -> std::vector<uint8_t>+parse_stream_rate_env() -> StreamRateCfg. Three internal builders (legacy 13B, HT 13B, VHT 22B) keyed offcfg.mode.StreamDuplexDemoandStreamTxDemoswitched from each demo's privatekRadiotapLegacy6M[13]constant to akStreamRadiotapvector built once at static-init from the env var.PrecoderDemointentionally untouched — its PoC plan explicitly locks the carrier to 6M.CMakeLists.txtupdated to compile the helper intoWiFiDriver.🤖 Generated with Claude Code