1 // SPDX-License-Identifier: ISC
3 * Copyright (C) 2019 Felix Fietkau <nbd@nbd.name>
6 #include <net/mac80211.h>
7 #include "ieee80211_i.h"
10 #define AVG_PKT_SIZE 1024
12 /* Number of bits for an average sized packet */
13 #define MCS_NBITS (AVG_PKT_SIZE << 3)
15 /* Number of kilo-symbols (symbols * 1024) for a packet with (bps) bits per
16 * symbol. We use k-symbols to avoid rounding in the _TIME macros below.
18 #define MCS_N_KSYMS(bps) DIV_ROUND_UP(MCS_NBITS << 10, (bps))
20 /* Transmission time (in 1024 * usec) for a packet containing (ksyms) * 1024
23 #define MCS_SYMBOL_TIME(sgi, ksyms) \
25 ((ksyms) * 4 * 18) / 20 : /* 3.6 us per sym */ \
26 ((ksyms) * 4) /* 4.0 us per sym */ \
29 /* Transmit duration for the raw data part of an average sized packet */
30 #define MCS_DURATION(streams, sgi, bps) \
31 ((u32)MCS_SYMBOL_TIME(sgi, MCS_N_KSYMS((streams) * (bps))))
33 #define MCS_DURATION_S(shift, streams, sgi, bps) \
34 ((u16)((MCS_DURATION(streams, sgi, bps) >> shift)))
36 /* These should match the values in enum nl80211_he_gi */
41 /* Transmission time (1024 usec) for a packet containing (ksyms) * k-symbols */
42 #define HE_SYMBOL_TIME(gi, ksyms) \
44 ((ksyms) * 16 * 17) / 20 : /* 13.6 us per sym */ \
46 ((ksyms) * 16 * 18) / 20 : /* 14.4 us per sym */ \
47 ((ksyms) * 16) /* 16.0 us per sym */ \
50 /* Transmit duration for the raw data part of an average sized packet */
51 #define HE_DURATION(streams, gi, bps) \
52 ((u32)HE_SYMBOL_TIME(gi, MCS_N_KSYMS((streams) * (bps))))
54 #define HE_DURATION_S(shift, streams, gi, bps) \
55 (HE_DURATION(streams, gi, bps) >> shift)
63 * Define group sort order: HT40 -> SGI -> #streams
65 #define IEEE80211_MAX_STREAMS 4
66 #define IEEE80211_HT_STREAM_GROUPS 4 /* BW(=2) * SGI(=2) */
67 #define IEEE80211_VHT_STREAM_GROUPS 8 /* BW(=4) * SGI(=2) */
69 #define IEEE80211_HE_MAX_STREAMS 8
70 #define IEEE80211_HE_STREAM_GROUPS 12 /* BW(=4) * GI(=3) */
72 #define IEEE80211_HT_GROUPS_NB (IEEE80211_MAX_STREAMS * \
73 IEEE80211_HT_STREAM_GROUPS)
74 #define IEEE80211_VHT_GROUPS_NB (IEEE80211_MAX_STREAMS * \
75 IEEE80211_VHT_STREAM_GROUPS)
76 #define IEEE80211_HE_GROUPS_NB (IEEE80211_HE_MAX_STREAMS * \
77 IEEE80211_HE_STREAM_GROUPS)
78 #define IEEE80211_GROUPS_NB (IEEE80211_HT_GROUPS_NB + \
79 IEEE80211_VHT_GROUPS_NB + \
80 IEEE80211_HE_GROUPS_NB)
82 #define IEEE80211_HT_GROUP_0 0
83 #define IEEE80211_VHT_GROUP_0 (IEEE80211_HT_GROUP_0 + IEEE80211_HT_GROUPS_NB)
84 #define IEEE80211_HE_GROUP_0 (IEEE80211_VHT_GROUP_0 + IEEE80211_VHT_GROUPS_NB)
86 #define MCS_GROUP_RATES 12
88 #define HT_GROUP_IDX(_streams, _sgi, _ht40) \
89 IEEE80211_HT_GROUP_0 + \
90 IEEE80211_MAX_STREAMS * 2 * _ht40 + \
91 IEEE80211_MAX_STREAMS * _sgi + \
94 #define _MAX(a, b) (((a)>(b))?(a):(b))
96 #define GROUP_SHIFT(duration) \
97 _MAX(0, 16 - __builtin_clz(duration))
99 /* MCS rate information for an MCS group */
100 #define __MCS_GROUP(_streams, _sgi, _ht40, _s) \
101 [HT_GROUP_IDX(_streams, _sgi, _ht40)] = { \
104 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 54 : 26), \
105 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 108 : 52), \
106 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 162 : 78), \
107 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 216 : 104), \
108 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 324 : 156), \
109 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 432 : 208), \
110 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 486 : 234), \
111 MCS_DURATION_S(_s, _streams, _sgi, _ht40 ? 540 : 260) \
115 #define MCS_GROUP_SHIFT(_streams, _sgi, _ht40) \
116 GROUP_SHIFT(MCS_DURATION(_streams, _sgi, _ht40 ? 54 : 26))
118 #define MCS_GROUP(_streams, _sgi, _ht40) \
119 __MCS_GROUP(_streams, _sgi, _ht40, \
120 MCS_GROUP_SHIFT(_streams, _sgi, _ht40))
122 #define VHT_GROUP_IDX(_streams, _sgi, _bw) \
123 (IEEE80211_VHT_GROUP_0 + \
124 IEEE80211_MAX_STREAMS * 2 * (_bw) + \
125 IEEE80211_MAX_STREAMS * (_sgi) + \
128 #define BW2VBPS(_bw, r4, r3, r2, r1) \
129 (_bw == BW_160 ? r4 : _bw == BW_80 ? r3 : _bw == BW_40 ? r2 : r1)
131 #define __VHT_GROUP(_streams, _sgi, _bw, _s) \
132 [VHT_GROUP_IDX(_streams, _sgi, _bw)] = { \
135 MCS_DURATION_S(_s, _streams, _sgi, \
136 BW2VBPS(_bw, 234, 117, 54, 26)), \
137 MCS_DURATION_S(_s, _streams, _sgi, \
138 BW2VBPS(_bw, 468, 234, 108, 52)), \
139 MCS_DURATION_S(_s, _streams, _sgi, \
140 BW2VBPS(_bw, 702, 351, 162, 78)), \
141 MCS_DURATION_S(_s, _streams, _sgi, \
142 BW2VBPS(_bw, 936, 468, 216, 104)), \
143 MCS_DURATION_S(_s, _streams, _sgi, \
144 BW2VBPS(_bw, 1404, 702, 324, 156)), \
145 MCS_DURATION_S(_s, _streams, _sgi, \
146 BW2VBPS(_bw, 1872, 936, 432, 208)), \
147 MCS_DURATION_S(_s, _streams, _sgi, \
148 BW2VBPS(_bw, 2106, 1053, 486, 234)), \
149 MCS_DURATION_S(_s, _streams, _sgi, \
150 BW2VBPS(_bw, 2340, 1170, 540, 260)), \
151 MCS_DURATION_S(_s, _streams, _sgi, \
152 BW2VBPS(_bw, 2808, 1404, 648, 312)), \
153 MCS_DURATION_S(_s, _streams, _sgi, \
154 BW2VBPS(_bw, 3120, 1560, 720, 346)) \
158 #define VHT_GROUP_SHIFT(_streams, _sgi, _bw) \
159 GROUP_SHIFT(MCS_DURATION(_streams, _sgi, \
160 BW2VBPS(_bw, 243, 117, 54, 26)))
162 #define VHT_GROUP(_streams, _sgi, _bw) \
163 __VHT_GROUP(_streams, _sgi, _bw, \
164 VHT_GROUP_SHIFT(_streams, _sgi, _bw))
167 #define HE_GROUP_IDX(_streams, _gi, _bw) \
168 (IEEE80211_HE_GROUP_0 + \
169 IEEE80211_HE_MAX_STREAMS * 3 * (_bw) + \
170 IEEE80211_HE_MAX_STREAMS * (_gi) + \
173 #define __HE_GROUP(_streams, _gi, _bw, _s) \
174 [HE_GROUP_IDX(_streams, _gi, _bw)] = { \
177 HE_DURATION_S(_s, _streams, _gi, \
178 BW2VBPS(_bw, 979, 489, 230, 115)), \
179 HE_DURATION_S(_s, _streams, _gi, \
180 BW2VBPS(_bw, 1958, 979, 475, 230)), \
181 HE_DURATION_S(_s, _streams, _gi, \
182 BW2VBPS(_bw, 2937, 1468, 705, 345)), \
183 HE_DURATION_S(_s, _streams, _gi, \
184 BW2VBPS(_bw, 3916, 1958, 936, 475)), \
185 HE_DURATION_S(_s, _streams, _gi, \
186 BW2VBPS(_bw, 5875, 2937, 1411, 705)), \
187 HE_DURATION_S(_s, _streams, _gi, \
188 BW2VBPS(_bw, 7833, 3916, 1872, 936)), \
189 HE_DURATION_S(_s, _streams, _gi, \
190 BW2VBPS(_bw, 8827, 4406, 2102, 1051)), \
191 HE_DURATION_S(_s, _streams, _gi, \
192 BW2VBPS(_bw, 9806, 4896, 2347, 1166)), \
193 HE_DURATION_S(_s, _streams, _gi, \
194 BW2VBPS(_bw, 11764, 5875, 2808, 1411)), \
195 HE_DURATION_S(_s, _streams, _gi, \
196 BW2VBPS(_bw, 13060, 6523, 3124, 1555)), \
197 HE_DURATION_S(_s, _streams, _gi, \
198 BW2VBPS(_bw, 14702, 7344, 3513, 1756)), \
199 HE_DURATION_S(_s, _streams, _gi, \
200 BW2VBPS(_bw, 16329, 8164, 3902, 1944)) \
204 #define HE_GROUP_SHIFT(_streams, _gi, _bw) \
205 GROUP_SHIFT(HE_DURATION(_streams, _gi, \
206 BW2VBPS(_bw, 979, 489, 230, 115)))
208 #define HE_GROUP(_streams, _gi, _bw) \
209 __HE_GROUP(_streams, _gi, _bw, \
210 HE_GROUP_SHIFT(_streams, _gi, _bw))
213 u16 duration[MCS_GROUP_RATES];
216 static const struct mcs_group airtime_mcs_groups[] = {
217 MCS_GROUP(1, 0, BW_20),
218 MCS_GROUP(2, 0, BW_20),
219 MCS_GROUP(3, 0, BW_20),
220 MCS_GROUP(4, 0, BW_20),
222 MCS_GROUP(1, 1, BW_20),
223 MCS_GROUP(2, 1, BW_20),
224 MCS_GROUP(3, 1, BW_20),
225 MCS_GROUP(4, 1, BW_20),
227 MCS_GROUP(1, 0, BW_40),
228 MCS_GROUP(2, 0, BW_40),
229 MCS_GROUP(3, 0, BW_40),
230 MCS_GROUP(4, 0, BW_40),
232 MCS_GROUP(1, 1, BW_40),
233 MCS_GROUP(2, 1, BW_40),
234 MCS_GROUP(3, 1, BW_40),
235 MCS_GROUP(4, 1, BW_40),
237 VHT_GROUP(1, 0, BW_20),
238 VHT_GROUP(2, 0, BW_20),
239 VHT_GROUP(3, 0, BW_20),
240 VHT_GROUP(4, 0, BW_20),
242 VHT_GROUP(1, 1, BW_20),
243 VHT_GROUP(2, 1, BW_20),
244 VHT_GROUP(3, 1, BW_20),
245 VHT_GROUP(4, 1, BW_20),
247 VHT_GROUP(1, 0, BW_40),
248 VHT_GROUP(2, 0, BW_40),
249 VHT_GROUP(3, 0, BW_40),
250 VHT_GROUP(4, 0, BW_40),
252 VHT_GROUP(1, 1, BW_40),
253 VHT_GROUP(2, 1, BW_40),
254 VHT_GROUP(3, 1, BW_40),
255 VHT_GROUP(4, 1, BW_40),
257 VHT_GROUP(1, 0, BW_80),
258 VHT_GROUP(2, 0, BW_80),
259 VHT_GROUP(3, 0, BW_80),
260 VHT_GROUP(4, 0, BW_80),
262 VHT_GROUP(1, 1, BW_80),
263 VHT_GROUP(2, 1, BW_80),
264 VHT_GROUP(3, 1, BW_80),
265 VHT_GROUP(4, 1, BW_80),
267 VHT_GROUP(1, 0, BW_160),
268 VHT_GROUP(2, 0, BW_160),
269 VHT_GROUP(3, 0, BW_160),
270 VHT_GROUP(4, 0, BW_160),
272 VHT_GROUP(1, 1, BW_160),
273 VHT_GROUP(2, 1, BW_160),
274 VHT_GROUP(3, 1, BW_160),
275 VHT_GROUP(4, 1, BW_160),
277 HE_GROUP(1, HE_GI_08, BW_20),
278 HE_GROUP(2, HE_GI_08, BW_20),
279 HE_GROUP(3, HE_GI_08, BW_20),
280 HE_GROUP(4, HE_GI_08, BW_20),
281 HE_GROUP(5, HE_GI_08, BW_20),
282 HE_GROUP(6, HE_GI_08, BW_20),
283 HE_GROUP(7, HE_GI_08, BW_20),
284 HE_GROUP(8, HE_GI_08, BW_20),
286 HE_GROUP(1, HE_GI_16, BW_20),
287 HE_GROUP(2, HE_GI_16, BW_20),
288 HE_GROUP(3, HE_GI_16, BW_20),
289 HE_GROUP(4, HE_GI_16, BW_20),
290 HE_GROUP(5, HE_GI_16, BW_20),
291 HE_GROUP(6, HE_GI_16, BW_20),
292 HE_GROUP(7, HE_GI_16, BW_20),
293 HE_GROUP(8, HE_GI_16, BW_20),
295 HE_GROUP(1, HE_GI_32, BW_20),
296 HE_GROUP(2, HE_GI_32, BW_20),
297 HE_GROUP(3, HE_GI_32, BW_20),
298 HE_GROUP(4, HE_GI_32, BW_20),
299 HE_GROUP(5, HE_GI_32, BW_20),
300 HE_GROUP(6, HE_GI_32, BW_20),
301 HE_GROUP(7, HE_GI_32, BW_20),
302 HE_GROUP(8, HE_GI_32, BW_20),
304 HE_GROUP(1, HE_GI_08, BW_40),
305 HE_GROUP(2, HE_GI_08, BW_40),
306 HE_GROUP(3, HE_GI_08, BW_40),
307 HE_GROUP(4, HE_GI_08, BW_40),
308 HE_GROUP(5, HE_GI_08, BW_40),
309 HE_GROUP(6, HE_GI_08, BW_40),
310 HE_GROUP(7, HE_GI_08, BW_40),
311 HE_GROUP(8, HE_GI_08, BW_40),
313 HE_GROUP(1, HE_GI_16, BW_40),
314 HE_GROUP(2, HE_GI_16, BW_40),
315 HE_GROUP(3, HE_GI_16, BW_40),
316 HE_GROUP(4, HE_GI_16, BW_40),
317 HE_GROUP(5, HE_GI_16, BW_40),
318 HE_GROUP(6, HE_GI_16, BW_40),
319 HE_GROUP(7, HE_GI_16, BW_40),
320 HE_GROUP(8, HE_GI_16, BW_40),
322 HE_GROUP(1, HE_GI_32, BW_40),
323 HE_GROUP(2, HE_GI_32, BW_40),
324 HE_GROUP(3, HE_GI_32, BW_40),
325 HE_GROUP(4, HE_GI_32, BW_40),
326 HE_GROUP(5, HE_GI_32, BW_40),
327 HE_GROUP(6, HE_GI_32, BW_40),
328 HE_GROUP(7, HE_GI_32, BW_40),
329 HE_GROUP(8, HE_GI_32, BW_40),
331 HE_GROUP(1, HE_GI_08, BW_80),
332 HE_GROUP(2, HE_GI_08, BW_80),
333 HE_GROUP(3, HE_GI_08, BW_80),
334 HE_GROUP(4, HE_GI_08, BW_80),
335 HE_GROUP(5, HE_GI_08, BW_80),
336 HE_GROUP(6, HE_GI_08, BW_80),
337 HE_GROUP(7, HE_GI_08, BW_80),
338 HE_GROUP(8, HE_GI_08, BW_80),
340 HE_GROUP(1, HE_GI_16, BW_80),
341 HE_GROUP(2, HE_GI_16, BW_80),
342 HE_GROUP(3, HE_GI_16, BW_80),
343 HE_GROUP(4, HE_GI_16, BW_80),
344 HE_GROUP(5, HE_GI_16, BW_80),
345 HE_GROUP(6, HE_GI_16, BW_80),
346 HE_GROUP(7, HE_GI_16, BW_80),
347 HE_GROUP(8, HE_GI_16, BW_80),
349 HE_GROUP(1, HE_GI_32, BW_80),
350 HE_GROUP(2, HE_GI_32, BW_80),
351 HE_GROUP(3, HE_GI_32, BW_80),
352 HE_GROUP(4, HE_GI_32, BW_80),
353 HE_GROUP(5, HE_GI_32, BW_80),
354 HE_GROUP(6, HE_GI_32, BW_80),
355 HE_GROUP(7, HE_GI_32, BW_80),
356 HE_GROUP(8, HE_GI_32, BW_80),
358 HE_GROUP(1, HE_GI_08, BW_160),
359 HE_GROUP(2, HE_GI_08, BW_160),
360 HE_GROUP(3, HE_GI_08, BW_160),
361 HE_GROUP(4, HE_GI_08, BW_160),
362 HE_GROUP(5, HE_GI_08, BW_160),
363 HE_GROUP(6, HE_GI_08, BW_160),
364 HE_GROUP(7, HE_GI_08, BW_160),
365 HE_GROUP(8, HE_GI_08, BW_160),
367 HE_GROUP(1, HE_GI_16, BW_160),
368 HE_GROUP(2, HE_GI_16, BW_160),
369 HE_GROUP(3, HE_GI_16, BW_160),
370 HE_GROUP(4, HE_GI_16, BW_160),
371 HE_GROUP(5, HE_GI_16, BW_160),
372 HE_GROUP(6, HE_GI_16, BW_160),
373 HE_GROUP(7, HE_GI_16, BW_160),
374 HE_GROUP(8, HE_GI_16, BW_160),
376 HE_GROUP(1, HE_GI_32, BW_160),
377 HE_GROUP(2, HE_GI_32, BW_160),
378 HE_GROUP(3, HE_GI_32, BW_160),
379 HE_GROUP(4, HE_GI_32, BW_160),
380 HE_GROUP(5, HE_GI_32, BW_160),
381 HE_GROUP(6, HE_GI_32, BW_160),
382 HE_GROUP(7, HE_GI_32, BW_160),
383 HE_GROUP(8, HE_GI_32, BW_160),
387 ieee80211_calc_legacy_rate_duration(u16 bitrate, bool short_pre,
393 duration = 144 + 48; /* preamble + PLCP */
397 duration += 10; /* SIFS */
399 duration = 20 + 16; /* premable + SIFS */
403 duration += (len * 10) / bitrate;
408 u32 ieee80211_calc_rx_airtime(struct ieee80211_hw *hw,
409 struct ieee80211_rx_status *status,
412 struct ieee80211_supported_band *sband;
413 const struct ieee80211_rate *rate;
414 bool sgi = status->enc_flags & RX_ENC_FLAG_SHORT_GI;
415 bool sp = status->enc_flags & RX_ENC_FLAG_SHORTPRE;
421 switch (status->bw) {
422 case RATE_INFO_BW_20:
425 case RATE_INFO_BW_40:
428 case RATE_INFO_BW_80:
431 case RATE_INFO_BW_160:
439 switch (status->encoding) {
441 if (WARN_ON_ONCE(status->band > NL80211_BAND_5GHZ))
444 sband = hw->wiphy->bands[status->band];
445 if (!sband || status->rate_idx >= sband->n_bitrates)
448 rate = &sband->bitrates[status->rate_idx];
449 cck = rate->flags & IEEE80211_RATE_MANDATORY_B;
451 return ieee80211_calc_legacy_rate_duration(rate->bitrate, sp,
455 streams = status->nss;
456 idx = status->rate_idx;
457 group = VHT_GROUP_IDX(streams, sgi, bw);
460 streams = ((status->rate_idx >> 3) & 3) + 1;
461 idx = status->rate_idx & 7;
462 group = HT_GROUP_IDX(streams, sgi, bw);
465 streams = status->nss;
466 idx = status->rate_idx;
467 group = HE_GROUP_IDX(streams, status->he_gi, bw);
474 if (WARN_ON_ONCE((status->encoding != RX_ENC_HE && streams > 4) ||
475 (status->encoding == RX_ENC_HE && streams > 8)))
478 duration = airtime_mcs_groups[group].duration[idx];
479 duration <<= airtime_mcs_groups[group].shift;
481 duration /= AVG_PKT_SIZE;
484 duration += 36 + (streams << 2);
488 EXPORT_SYMBOL_GPL(ieee80211_calc_rx_airtime);
490 static u32 ieee80211_calc_tx_airtime_rate(struct ieee80211_hw *hw,
491 struct ieee80211_tx_rate *rate,
494 struct ieee80211_rx_status stat = {
498 if (rate->idx < 0 || !rate->count)
501 if (rate->flags & IEEE80211_TX_RC_80_MHZ_WIDTH)
502 stat.bw = RATE_INFO_BW_80;
503 else if (rate->flags & IEEE80211_TX_RC_40_MHZ_WIDTH)
504 stat.bw = RATE_INFO_BW_40;
506 stat.bw = RATE_INFO_BW_20;
509 if (rate->flags & IEEE80211_TX_RC_USE_SHORT_PREAMBLE)
510 stat.enc_flags |= RX_ENC_FLAG_SHORTPRE;
511 if (rate->flags & IEEE80211_TX_RC_SHORT_GI)
512 stat.enc_flags |= RX_ENC_FLAG_SHORT_GI;
514 stat.rate_idx = rate->idx;
515 if (rate->flags & IEEE80211_TX_RC_VHT_MCS) {
516 stat.encoding = RX_ENC_VHT;
517 stat.rate_idx = ieee80211_rate_get_vht_mcs(rate);
518 stat.nss = ieee80211_rate_get_vht_nss(rate);
519 } else if (rate->flags & IEEE80211_TX_RC_MCS) {
520 stat.encoding = RX_ENC_HT;
522 stat.encoding = RX_ENC_LEGACY;
525 return ieee80211_calc_rx_airtime(hw, &stat, len);
528 u32 ieee80211_calc_tx_airtime(struct ieee80211_hw *hw,
529 struct ieee80211_tx_info *info,
535 for (i = 0; i < ARRAY_SIZE(info->status.rates); i++) {
536 struct ieee80211_tx_rate *rate = &info->status.rates[i];
539 cur_duration = ieee80211_calc_tx_airtime_rate(hw, rate,
544 duration += cur_duration * rate->count;
549 EXPORT_SYMBOL_GPL(ieee80211_calc_tx_airtime);
551 u32 ieee80211_calc_expected_tx_airtime(struct ieee80211_hw *hw,
552 struct ieee80211_vif *vif,
553 struct ieee80211_sta *pubsta,
556 struct ieee80211_supported_band *sband;
557 struct ieee80211_chanctx_conf *conf;
558 int rateidx, shift = 0;
559 bool cck, short_pream;
564 len += 38; /* Ethernet header length */
566 conf = rcu_dereference(vif->chanctx_conf);
568 band = conf->def.chan->band;
569 shift = ieee80211_chandef_get_shift(&conf->def);
573 struct sta_info *sta = container_of(pubsta, struct sta_info,
576 return ieee80211_calc_tx_airtime_rate(hw,
577 &sta->tx_stats.last_rate,
584 /* No station to get latest rate from, so calculate the worst-case
585 * duration using the lowest configured basic rate.
587 sband = hw->wiphy->bands[band];
589 basic_rates = vif->bss_conf.basic_rates;
590 short_pream = vif->bss_conf.use_short_preamble;
592 rateidx = basic_rates ? ffs(basic_rates) - 1 : 0;
593 rate = sband->bitrates[rateidx].bitrate << shift;
594 cck = sband->bitrates[rateidx].flags & IEEE80211_RATE_MANDATORY_B;
596 return ieee80211_calc_legacy_rate_duration(rate, short_pream, cck, len);