On Wed September 15 2010 09:44:09 Jonathan Guerin wrote: > The timings I used were from the 802.11-2007 spec. > SIFS, DIFS & Slot Time: Table 17-15—OFDM PHY characteristics > NDPS values: Table 17-3—Modulation-dependent parameters > txtime calculations: Section 17.4.3 OFDM TXTIME calculation > > Here are the functions I use to do the basics: > int16_t ndbps(uint8_t rate_Mbps) > { > //Radiotap returns rate in 500kbps units > rate_Mbps/=2; > > static const uint8_t rate_nsyms[][2] = { > { 6, 24 }, > { 9, 36 }, > { 12, 48 }, > { 18, 72 }, > { 24, 96 }, > { 36, 144 }, > { 48, 192 }, > { 54, 216 } this is rate * 4 > }; > static const size_t nof_rate_nsyms = sizeof(rate_nsyms) / > sizeof(rate_nsyms[0]); > for(size_t i = 0; i < nof_rate_nsyms; ++i) { > if(rate_Mbps == rate_nsyms[i][0]) { > return rate_nsyms[i][1]; > } > } > return -1; > } > > int getTXTime(int rate, int noctets) { > uint16_t usecs = 0; > const int16_t nof_bps = ndbps(rate); > > int chan_rate = 1; > > if(-1 != nof_bps) { > const uint16_t preamble = 16 * chan_rate; > const uint16_t signal = 4 * chan_rate; > const uint16_t tsym = 4 * chan_rate; > const uint16_t nsyms = ceill((16.0 + 8.0 * (noctets) + 6.0) / nof_bps); > usecs = preamble + signal + tsym * nsyms; > } > > return(usecs); if you compare that to the code in mac80211/util.c ieee80211_frame_duration(): dur = 16; /* SIFS + signal ext */ dur += 16; /* 17.3.2.3: T_PREAMBLE = 16 usec */ dur += 4; /* 17.3.2.3: T_SIGNAL = 4 usec */ dur += 4 * DIV_ROUND_UP((16 + 8 * (len + 4) + 6) * 10, 4 * rate); /* T_SYM x N_SYM */ it is equivalent, except that you don't add 16 /* SIFS + signal ext */. is this intended? bruno -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html