xref: /freebsd/sys/net80211/ieee80211_phy.c (revision fe267a559009cbf34f9341666fe4d88a92c02d5e)

/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2007-2008 Sam Leffler, Errno Consulting
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

/*
 * IEEE 802.11 PHY-related support.
 */

#include "opt_inet.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/malloc.h>

#include <sys/socket.h>

#include <net/if.h>
#include <net/if_media.h>

#include <net/ethernet.h>
#include <net/route.h>

#include <net80211/ieee80211_var.h>
#include <net80211/ieee80211_phy.h>

#ifdef notyet
struct ieee80211_ds_plcp_hdr {
	uint8_t		i_signal;
	uint8_t		i_service;
	uint16_t	i_length;
	uint16_t	i_crc;
} __packed;

#endif	/* notyet */

/* shorthands to compact tables for readability */
#define	OFDM	IEEE80211_T_OFDM
#define	CCK	IEEE80211_T_CCK
#define	TURBO	IEEE80211_T_TURBO
#define	HALF	IEEE80211_T_OFDM_HALF
#define	QUART	IEEE80211_T_OFDM_QUARTER
#define	HT	IEEE80211_T_HT
/* XXX the 11n and the basic rate flag are unfortunately overlapping. Grr. */
#define	N(r)	(IEEE80211_RATE_MCS | r)
#define	PBCC	(IEEE80211_T_OFDM_QUARTER+1)		/* XXX */
#define	B(r)	(IEEE80211_RATE_BASIC | r)
#define	Mb(x)	(x*1000)

static struct ieee80211_rate_table ieee80211_11b_table = {
    .rateCount = 4,		/* XXX no PBCC */
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = CCK,     1000,    0x00,      B(2),   0 },/*   1 Mb */
     [1] = { .phy = CCK,     2000,    0x04,      B(4),   1 },/*   2 Mb */
     [2] = { .phy = CCK,     5500,    0x04,     B(11),   1 },/* 5.5 Mb */
     [3] = { .phy = CCK,    11000,    0x04,     B(22),   1 },/*  11 Mb */
     [4] = { .phy = PBCC,   22000,    0x04,        44,   3 } /*  22 Mb */
    },
};

static struct ieee80211_rate_table ieee80211_11g_table = {
    .rateCount = 12,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = CCK,     1000,    0x00,      B(2),   0 },
     [1] = { .phy = CCK,     2000,    0x04,      B(4),   1 },
     [2] = { .phy = CCK,     5500,    0x04,     B(11),   2 },
     [3] = { .phy = CCK,    11000,    0x04,     B(22),   3 },
     [4] = { .phy = OFDM,    6000,    0x00,        12,   4 },
     [5] = { .phy = OFDM,    9000,    0x00,        18,   4 },
     [6] = { .phy = OFDM,   12000,    0x00,        24,   6 },
     [7] = { .phy = OFDM,   18000,    0x00,        36,   6 },
     [8] = { .phy = OFDM,   24000,    0x00,        48,   8 },
     [9] = { .phy = OFDM,   36000,    0x00,        72,   8 },
    [10] = { .phy = OFDM,   48000,    0x00,        96,   8 },
    [11] = { .phy = OFDM,   54000,    0x00,       108,   8 }
    },
};

static struct ieee80211_rate_table ieee80211_11a_table = {
    .rateCount = 8,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = OFDM,    6000,    0x00,     B(12),   0 },
     [1] = { .phy = OFDM,    9000,    0x00,        18,   0 },
     [2] = { .phy = OFDM,   12000,    0x00,     B(24),   2 },
     [3] = { .phy = OFDM,   18000,    0x00,        36,   2 },
     [4] = { .phy = OFDM,   24000,    0x00,     B(48),   4 },
     [5] = { .phy = OFDM,   36000,    0x00,        72,   4 },
     [6] = { .phy = OFDM,   48000,    0x00,        96,   4 },
     [7] = { .phy = OFDM,   54000,    0x00,       108,   4 }
    },
};

static struct ieee80211_rate_table ieee80211_half_table = {
    .rateCount = 8,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = HALF,    3000,    0x00,      B(6),   0 },
     [1] = { .phy = HALF,    4500,    0x00,         9,   0 },
     [2] = { .phy = HALF,    6000,    0x00,     B(12),   2 },
     [3] = { .phy = HALF,    9000,    0x00,        18,   2 },
     [4] = { .phy = HALF,   12000,    0x00,     B(24),   4 },
     [5] = { .phy = HALF,   18000,    0x00,        36,   4 },
     [6] = { .phy = HALF,   24000,    0x00,        48,   4 },
     [7] = { .phy = HALF,   27000,    0x00,        54,   4 }
    },
};

static struct ieee80211_rate_table ieee80211_quarter_table = {
    .rateCount = 8,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = QUART,   1500,    0x00,      B(3),   0 },
     [1] = { .phy = QUART,   2250,    0x00,         4,   0 },
     [2] = { .phy = QUART,   3000,    0x00,      B(9),   2 },
     [3] = { .phy = QUART,   4500,    0x00,         9,   2 },
     [4] = { .phy = QUART,   6000,    0x00,     B(12),   4 },
     [5] = { .phy = QUART,   9000,    0x00,        18,   4 },
     [6] = { .phy = QUART,  12000,    0x00,        24,   4 },
     [7] = { .phy = QUART,  13500,    0x00,        27,   4 }
    },
};

static struct ieee80211_rate_table ieee80211_turbog_table = {
    .rateCount = 7,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = TURBO,   12000,   0x00,     B(12),   0 },
     [1] = { .phy = TURBO,   24000,   0x00,     B(24),   1 },
     [2] = { .phy = TURBO,   36000,   0x00,        36,   1 },
     [3] = { .phy = TURBO,   48000,   0x00,     B(48),   3 },
     [4] = { .phy = TURBO,   72000,   0x00,        72,   3 },
     [5] = { .phy = TURBO,   96000,   0x00,        96,   3 },
     [6] = { .phy = TURBO,  108000,   0x00,       108,   3 }
    },
};

static struct ieee80211_rate_table ieee80211_turboa_table = {
    .rateCount = 8,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = TURBO,   12000,   0x00,     B(12),   0 },
     [1] = { .phy = TURBO,   18000,   0x00,        18,   0 },
     [2] = { .phy = TURBO,   24000,   0x00,     B(24),   2 },
     [3] = { .phy = TURBO,   36000,   0x00,        36,   2 },
     [4] = { .phy = TURBO,   48000,   0x00,     B(48),   4 },
     [5] = { .phy = TURBO,   72000,   0x00,        72,   4 },
     [6] = { .phy = TURBO,   96000,   0x00,        96,   4 },
     [7] = { .phy = TURBO,  108000,   0x00,       108,   4 }
    },
};

static struct ieee80211_rate_table ieee80211_11ng_table = {
    .rateCount = 36,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = CCK,     1000,    0x00,      B(2),   0 },
     [1] = { .phy = CCK,     2000,    0x04,      B(4),   1 },
     [2] = { .phy = CCK,     5500,    0x04,     B(11),   2 },
     [3] = { .phy = CCK,    11000,    0x04,     B(22),   3 },
     [4] = { .phy = OFDM,    6000,    0x00,        12,   4 },
     [5] = { .phy = OFDM,    9000,    0x00,        18,   4 },
     [6] = { .phy = OFDM,   12000,    0x00,        24,   6 },
     [7] = { .phy = OFDM,   18000,    0x00,        36,   6 },
     [8] = { .phy = OFDM,   24000,    0x00,        48,   8 },
     [9] = { .phy = OFDM,   36000,    0x00,        72,   8 },
    [10] = { .phy = OFDM,   48000,    0x00,        96,   8 },
    [11] = { .phy = OFDM,   54000,    0x00,       108,   8 },

    [12] = { .phy = HT,      6500,    0x00,      N(0),   4 },
    [13] = { .phy = HT,     13000,    0x00,      N(1),   6 },
    [14] = { .phy = HT,     19500,    0x00,      N(2),   6 },
    [15] = { .phy = HT,     26000,    0x00,      N(3),   8 },
    [16] = { .phy = HT,     39000,    0x00,      N(4),   8 },
    [17] = { .phy = HT,     52000,    0x00,      N(5),   8 },
    [18] = { .phy = HT,     58500,    0x00,      N(6),   8 },
    [19] = { .phy = HT,     65000,    0x00,      N(7),   8 },

    [20] = { .phy = HT,     13000,    0x00,      N(8),   4 },
    [21] = { .phy = HT,     26000,    0x00,      N(9),   6 },
    [22] = { .phy = HT,     39000,    0x00,     N(10),   6 },
    [23] = { .phy = HT,     52000,    0x00,     N(11),   8 },
    [24] = { .phy = HT,     78000,    0x00,     N(12),   8 },
    [25] = { .phy = HT,    104000,    0x00,     N(13),   8 },
    [26] = { .phy = HT,    117000,    0x00,     N(14),   8 },
    [27] = { .phy = HT,    130000,    0x00,     N(15),   8 },

    [28] = { .phy = HT,     19500,    0x00,     N(16),   4 },
    [29] = { .phy = HT,     39000,    0x00,     N(17),   6 },
    [30] = { .phy = HT,     58500,    0x00,     N(18),   6 },
    [31] = { .phy = HT,     78000,    0x00,     N(19),   8 },
    [32] = { .phy = HT,    117000,    0x00,     N(20),   8 },
    [33] = { .phy = HT,    156000,    0x00,     N(21),   8 },
    [34] = { .phy = HT,    175500,    0x00,     N(22),   8 },
    [35] = { .phy = HT,    195000,    0x00,     N(23),   8 },

    },
};

static struct ieee80211_rate_table ieee80211_11na_table = {
    .rateCount = 32,
    .info = {
/*                                   short            ctrl  */
/*                                Preamble  dot11Rate Rate */
     [0] = { .phy = OFDM,    6000,    0x00,     B(12),   0 },
     [1] = { .phy = OFDM,    9000,    0x00,        18,   0 },
     [2] = { .phy = OFDM,   12000,    0x00,     B(24),   2 },
     [3] = { .phy = OFDM,   18000,    0x00,        36,   2 },
     [4] = { .phy = OFDM,   24000,    0x00,     B(48),   4 },
     [5] = { .phy = OFDM,   36000,    0x00,        72,   4 },
     [6] = { .phy = OFDM,   48000,    0x00,        96,   4 },
     [7] = { .phy = OFDM,   54000,    0x00,       108,   4 },

     [8] = { .phy = HT,      6500,    0x00,      N(0),   0 },
     [9] = { .phy = HT,     13000,    0x00,      N(1),   2 },
    [10] = { .phy = HT,     19500,    0x00,      N(2),   2 },
    [11] = { .phy = HT,     26000,    0x00,      N(3),   4 },
    [12] = { .phy = HT,     39000,    0x00,      N(4),   4 },
    [13] = { .phy = HT,     52000,    0x00,      N(5),   4 },
    [14] = { .phy = HT,     58500,    0x00,      N(6),   4 },
    [15] = { .phy = HT,     65000,    0x00,      N(7),   4 },

    [16] = { .phy = HT,     13000,    0x00,      N(8),   0 },
    [17] = { .phy = HT,     26000,    0x00,      N(9),   2 },
    [18] = { .phy = HT,     39000,    0x00,     N(10),   2 },
    [19] = { .phy = HT,     52000,    0x00,     N(11),   4 },
    [20] = { .phy = HT,     78000,    0x00,     N(12),   4 },
    [21] = { .phy = HT,    104000,    0x00,     N(13),   4 },
    [22] = { .phy = HT,    117000,    0x00,     N(14),   4 },
    [23] = { .phy = HT,    130000,    0x00,     N(15),   4 },

    [24] = { .phy = HT,     19500,    0x00,     N(16),   0 },
    [25] = { .phy = HT,     39000,    0x00,     N(17),   2 },
    [26] = { .phy = HT,     58500,    0x00,     N(18),   2 },
    [27] = { .phy = HT,     78000,    0x00,     N(19),   4 },
    [28] = { .phy = HT,    117000,    0x00,     N(20),   4 },
    [29] = { .phy = HT,    156000,    0x00,     N(21),   4 },
    [30] = { .phy = HT,    175500,    0x00,     N(22),   4 },
    [31] = { .phy = HT,    195000,    0x00,     N(23),   4 },

    },
};

#undef	Mb
#undef	B
#undef	OFDM
#undef	HALF
#undef	QUART
#undef	CCK
#undef	TURBO
#undef	XR
#undef	HT
#undef	N

/*
 * Setup a rate table's reverse lookup table and fill in
 * ack durations.  The reverse lookup tables are assumed
 * to be initialized to zero (or at least the first entry).
 * We use this as a key that indicates whether or not
 * we've previously setup the reverse lookup table.
 *
 * XXX not reentrant, but shouldn't matter
 */
static void
ieee80211_setup_ratetable(struct ieee80211_rate_table *rt)
{
#define	WLAN_CTRL_FRAME_SIZE \
	(sizeof(struct ieee80211_frame_ack) + IEEE80211_CRC_LEN)

	int i;

	for (i = 0; i < nitems(rt->rateCodeToIndex); i++)
		rt->rateCodeToIndex[i] = (uint8_t) -1;
	for (i = 0; i < rt->rateCount; i++) {
		uint8_t code = rt->info[i].dot11Rate;
		uint8_t cix = rt->info[i].ctlRateIndex;
		uint8_t ctl_rate = rt->info[cix].dot11Rate;

		/*
		 * Map without the basic rate bit.
		 *
		 * It's up to the caller to ensure that the basic
		 * rate bit is stripped here.
		 *
		 * For HT, use the MCS rate bit.
		 */
		code &= IEEE80211_RATE_VAL;
		if (rt->info[i].phy == IEEE80211_T_HT) {
			code |= IEEE80211_RATE_MCS;
		}

		/* XXX assume the control rate is non-MCS? */
		ctl_rate &= IEEE80211_RATE_VAL;
		rt->rateCodeToIndex[code] = i;

		/*
		 * XXX for 11g the control rate to use for 5.5 and 11 Mb/s
		 *     depends on whether they are marked as basic rates;
		 *     the static tables are setup with an 11b-compatible
		 *     2Mb/s rate which will work but is suboptimal
		 *
		 * NB: Control rate is always less than or equal to the
		 *     current rate, so control rate's reverse lookup entry
		 *     has been installed and following call is safe.
		 */
		rt->info[i].lpAckDuration = ieee80211_compute_duration(rt,
			WLAN_CTRL_FRAME_SIZE, ctl_rate, 0);
		rt->info[i].spAckDuration = ieee80211_compute_duration(rt,
			WLAN_CTRL_FRAME_SIZE, ctl_rate, IEEE80211_F_SHPREAMBLE);
	}

#undef WLAN_CTRL_FRAME_SIZE
}

/* Setup all rate tables */
static void
ieee80211_phy_init(void)
{
	static struct ieee80211_rate_table * const ratetables[] = {
		&ieee80211_half_table,
		&ieee80211_quarter_table,
		&ieee80211_11na_table,
		&ieee80211_11ng_table,
		&ieee80211_turbog_table,
		&ieee80211_turboa_table,
		&ieee80211_11a_table,
		&ieee80211_11g_table,
		&ieee80211_11b_table
	};
	int i;

	for (i = 0; i < nitems(ratetables); ++i)
		ieee80211_setup_ratetable(ratetables[i]);

}
SYSINIT(wlan_phy, SI_SUB_DRIVERS, SI_ORDER_FIRST, ieee80211_phy_init, NULL);

const struct ieee80211_rate_table *
ieee80211_get_ratetable(struct ieee80211_channel *c)
{
	const struct ieee80211_rate_table *rt;

	/* XXX HT */
	if (IEEE80211_IS_CHAN_HALF(c))
		rt = &ieee80211_half_table;
	else if (IEEE80211_IS_CHAN_QUARTER(c))
		rt = &ieee80211_quarter_table;
	else if (IEEE80211_IS_CHAN_HTA(c))
		rt = &ieee80211_11na_table;
	else if (IEEE80211_IS_CHAN_HTG(c))
		rt = &ieee80211_11ng_table;
	else if (IEEE80211_IS_CHAN_108G(c))
		rt = &ieee80211_turbog_table;
	else if (IEEE80211_IS_CHAN_ST(c))
		rt = &ieee80211_turboa_table;
	else if (IEEE80211_IS_CHAN_TURBO(c))
		rt = &ieee80211_turboa_table;
	else if (IEEE80211_IS_CHAN_A(c))
		rt = &ieee80211_11a_table;
	else if (IEEE80211_IS_CHAN_ANYG(c))
		rt = &ieee80211_11g_table;
	else if (IEEE80211_IS_CHAN_B(c))
		rt = &ieee80211_11b_table;
	else {
		/* NB: should not get here */
		panic("%s: no rate table for channel; freq %u flags 0x%x\n",
		      __func__, c->ic_freq, c->ic_flags);
	}
	return rt;
}

/*
 * Convert PLCP signal/rate field to 802.11 rate (.5Mbits/s)
 *
 * Note we do no parameter checking; this routine is mainly
 * used to derive an 802.11 rate for constructing radiotap
 * header data for rx frames.
 *
 * XXX might be a candidate for inline
 */
uint8_t
ieee80211_plcp2rate(uint8_t plcp, enum ieee80211_phytype type)
{
	if (type == IEEE80211_T_OFDM) {
		static const uint8_t ofdm_plcp2rate[16] = {
			[0xb]	= 12,
			[0xf]	= 18,
			[0xa]	= 24,
			[0xe]	= 36,
			[0x9]	= 48,
			[0xd]	= 72,
			[0x8]	= 96,
			[0xc]	= 108
		};
		return ofdm_plcp2rate[plcp & 0xf];
	}
	if (type == IEEE80211_T_CCK) {
		static const uint8_t cck_plcp2rate[16] = {
			[0xa]	= 2,	/* 0x0a */
			[0x4]	= 4,	/* 0x14 */
			[0x7]	= 11,	/* 0x37 */
			[0xe]	= 22,	/* 0x6e */
			[0xc]	= 44,	/* 0xdc , actually PBCC */
		};
		return cck_plcp2rate[plcp & 0xf];
	}
	return 0;
}

/*
 * Covert 802.11 rate to PLCP signal.
 */
uint8_t
ieee80211_rate2plcp(int rate, enum ieee80211_phytype type)
{
	/* XXX ignore type for now since rates are unique */
	switch (rate) {
	/* OFDM rates (cf IEEE Std 802.11a-1999, pp. 14 Table 80) */
	case 12:	return 0xb;
	case 18:	return 0xf;
	case 24:	return 0xa;
	case 36:	return 0xe;
	case 48:	return 0x9;
	case 72:	return 0xd;
	case 96:	return 0x8;
	case 108:	return 0xc;
	/* CCK rates (IEEE Std 802.11b-1999 page 15, subclause 18.2.3.3) */
	case 2:		return 10;
	case 4:		return 20;
	case 11:	return 55;
	case 22:	return 110;
	/* IEEE Std 802.11g-2003 page 19, subclause 19.3.2.1 */
	case 44:	return 220;
	}
	return 0;		/* XXX unsupported/unknown rate */
}

#define CCK_SIFS_TIME		10
#define CCK_PREAMBLE_BITS	144
#define CCK_PLCP_BITS		48

#define OFDM_SIFS_TIME		16
#define OFDM_PREAMBLE_TIME	20
#define OFDM_PLCP_BITS		22
#define OFDM_SYMBOL_TIME	4

#define OFDM_HALF_SIFS_TIME	32
#define OFDM_HALF_PREAMBLE_TIME	40
#define OFDM_HALF_PLCP_BITS	22
#define OFDM_HALF_SYMBOL_TIME	8

#define OFDM_QUARTER_SIFS_TIME 		64
#define OFDM_QUARTER_PREAMBLE_TIME	80
#define OFDM_QUARTER_PLCP_BITS		22
#define OFDM_QUARTER_SYMBOL_TIME	16

#define TURBO_SIFS_TIME		8
#define TURBO_PREAMBLE_TIME	14
#define TURBO_PLCP_BITS		22
#define TURBO_SYMBOL_TIME	4

/*
 * Compute the time to transmit a frame of length frameLen bytes
 * using the specified rate, phy, and short preamble setting.
 * SIFS is included.
 */
uint16_t
ieee80211_compute_duration(const struct ieee80211_rate_table *rt,
	uint32_t frameLen, uint16_t rate, int isShortPreamble)
{
	uint8_t rix = rt->rateCodeToIndex[rate];
	uint32_t bitsPerSymbol, numBits, numSymbols, phyTime, txTime;
	uint32_t kbps;

	KASSERT(rix != (uint8_t)-1, ("rate %d has no info", rate));
	kbps = rt->info[rix].rateKbps;
	if (kbps == 0)			/* XXX bandaid for channel changes */
		return 0;

	switch (rt->info[rix].phy) {
	case IEEE80211_T_CCK:
		phyTime		= CCK_PREAMBLE_BITS + CCK_PLCP_BITS;
		if (isShortPreamble && rt->info[rix].shortPreamble)
			phyTime >>= 1;
		numBits		= frameLen << 3;
		txTime		= CCK_SIFS_TIME + phyTime
				+ ((numBits * 1000)/kbps);
		break;
	case IEEE80211_T_OFDM:
		bitsPerSymbol	= (kbps * OFDM_SYMBOL_TIME) / 1000;
		KASSERT(bitsPerSymbol != 0, ("full rate bps"));

		numBits		= OFDM_PLCP_BITS + (frameLen << 3);
		numSymbols	= howmany(numBits, bitsPerSymbol);
		txTime		= OFDM_SIFS_TIME
				+ OFDM_PREAMBLE_TIME
				+ (numSymbols * OFDM_SYMBOL_TIME);
		break;
	case IEEE80211_T_OFDM_HALF:
		bitsPerSymbol	= (kbps * OFDM_HALF_SYMBOL_TIME) / 1000;
		KASSERT(bitsPerSymbol != 0, ("1/4 rate bps"));

		numBits		= OFDM_PLCP_BITS + (frameLen << 3);
		numSymbols	= howmany(numBits, bitsPerSymbol);
		txTime		= OFDM_HALF_SIFS_TIME
				+ OFDM_HALF_PREAMBLE_TIME
				+ (numSymbols * OFDM_HALF_SYMBOL_TIME);
		break;
	case IEEE80211_T_OFDM_QUARTER:
		bitsPerSymbol	= (kbps * OFDM_QUARTER_SYMBOL_TIME) / 1000;
		KASSERT(bitsPerSymbol != 0, ("1/2 rate bps"));

		numBits		= OFDM_PLCP_BITS + (frameLen << 3);
		numSymbols	= howmany(numBits, bitsPerSymbol);
		txTime		= OFDM_QUARTER_SIFS_TIME
				+ OFDM_QUARTER_PREAMBLE_TIME
				+ (numSymbols * OFDM_QUARTER_SYMBOL_TIME);
		break;
	case IEEE80211_T_TURBO:
		/* we still save OFDM rates in kbps - so double them */
		bitsPerSymbol = ((kbps << 1) * TURBO_SYMBOL_TIME) / 1000;
		KASSERT(bitsPerSymbol != 0, ("turbo bps"));

		numBits       = TURBO_PLCP_BITS + (frameLen << 3);
		numSymbols    = howmany(numBits, bitsPerSymbol);
		txTime        = TURBO_SIFS_TIME + TURBO_PREAMBLE_TIME
			      + (numSymbols * TURBO_SYMBOL_TIME);
		break;
	default:
		panic("%s: unknown phy %u (rate %u)\n", __func__,
		      rt->info[rix].phy, rate);
	}
	return txTime;
}

static const uint16_t ht20_bps[32] = {
	26, 52, 78, 104, 156, 208, 234, 260,
	52, 104, 156, 208, 312, 416, 468, 520,
	78, 156, 234, 312, 468, 624, 702, 780,
	104, 208, 312, 416, 624, 832, 936, 1040
};
static const uint16_t ht40_bps[32] = {
	54, 108, 162, 216, 324, 432, 486, 540,
	108, 216, 324, 432, 648, 864, 972, 1080,
	162, 324, 486, 648, 972, 1296, 1458, 1620,
	216, 432, 648, 864, 1296, 1728, 1944, 2160
};


#define	OFDM_PLCP_BITS	22
#define	HT_L_STF	8
#define	HT_L_LTF	8
#define	HT_L_SIG	4
#define	HT_SIG		8
#define	HT_STF		4
#define	HT_LTF(n)	((n) * 4)

/*
 * Calculate the transmit duration of an 11n frame.
 */
uint32_t
ieee80211_compute_duration_ht(uint32_t frameLen, uint16_t rate,
    int streams, int isht40, int isShortGI)
{
	uint32_t bitsPerSymbol, numBits, numSymbols, txTime;

	KASSERT(rate & IEEE80211_RATE_MCS, ("not mcs %d", rate));
	KASSERT((rate &~ IEEE80211_RATE_MCS) < 31, ("bad mcs 0x%x", rate));

	if (isht40)
		bitsPerSymbol = ht40_bps[rate & 0x1f];
	else
		bitsPerSymbol = ht20_bps[rate & 0x1f];
	numBits = OFDM_PLCP_BITS + (frameLen << 3);
	numSymbols = howmany(numBits, bitsPerSymbol);
	if (isShortGI)
		txTime = ((numSymbols * 18) + 4) / 5;   /* 3.6us */
	else
		txTime = numSymbols * 4;                /* 4us */
	return txTime + HT_L_STF + HT_L_LTF +
	    HT_L_SIG + HT_SIG + HT_STF + HT_LTF(streams);
}

#undef	HT_LTF
#undef	HT_STF
#undef	HT_SIG
#undef	HT_L_SIG
#undef	HT_L_LTF
#undef	HT_L_STF
#undef	OFDM_PLCP_BITS