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Improved slottime and acktimeout/ctstimeout computations

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Needs field testing


git-svn-id: http://madwifi-project.org/svn/madwifi/trunk@3870 0192ed92-7a03-0410-a25b-9323aeb14dbd
This commit is contained in:
benoit 2008-11-03 15:15:28 +00:00
parent b327291039
commit a729fef8c6
1 changed files with 91 additions and 36 deletions
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127
ath/if_ath.c
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@ -4284,26 +4284,88 @@ ath_mode_init(struct net_device *dev)
rfilt, mfilt[0], mfilt[1]);
}
static inline int
ath_slottime2timeout(struct ath_softc *sc, int slottime)
/* returns aSIFSTime based on current channel settings */
static int
ath_default_sifs(struct ath_softc *sc)
{
/* IEEE 802.11 2007 9.2.8 says the ACK timeout shall be SIFSTime +
* slot time (+ PHY RX start delay). HAL seems to use a constant of 8
/* Turbo mode. FIXME : what is the correct value? */
if (sc->sc_dturbo || (sc->sc_curchan.privFlags & CHANNEL_ST))
return 8;
if (sc->sc_curchan.channelFlags & CHANNEL_2GHZ) {
/* default : 802.11b or 802.11g with short/long slot time */
return 10;
} else if (sc->sc_curchan.channelFlags & CHANNEL_5GHZ) {
/* 802.11a/10MHz (half rates) */
if (sc->sc_curchan.channelFlags & CHANNEL_HALF)
return 64;
/* 802.11a/5MHz (quarter rates) */
if (sc->sc_curchan.channelFlags & CHANNEL_QUARTER)
return 32;
/* default : 802.11a/20MHz */
return 16;
}
/* incorrect value for channelFlags, returns a default value */
return 10;
}
static inline int
ath_slottime2timeout(struct ath_softc *sc, int aSlotTime)
{
/* IEEE 802.11-2007 9.2.8 says the ACK timeout shall be aSIFSTime +
* aSlotTime (+ aPHY-RX-START-Delay). HAL seems to use a constant of 8
* for OFDM overhead and 18 for CCK overhead.
*
* XXX: Update based on emperical evidence (potentially save 15us per
* timeout). */
if (((sc->sc_curchan.channelFlags & IEEE80211_CHAN_A) ==
IEEE80211_CHAN_A) ||
(((sc->sc_curchan.channelFlags & IEEE80211_CHAN_108G) ==
IEEE80211_CHAN_108G) &&
(sc->sc_ic.ic_flags & IEEE80211_F_SHSLOT)))
/* Short slot time: 802.11a, and 802.11g turbo in turbo mode
* with short slot time. */
return slottime + 8;
else
/* Constant for CCK MIB processing time. */
return slottime + 18;
*/
int aSIFSTime;
aSIFSTime = ath_default_sifs(sc);
/* FIXME : we neglect aPHY-RX-START-Delay */
return aSIFSTime + aSlotTime;
}
/* returns aSlotTime in us based on the current channel settings. This value
* does not take into account air propagation time */
static int
ath_default_slottime(struct ath_softc *sc)
{
struct ieee80211com *ic = &sc->sc_ic;
/* Turbo mode */
if (sc->sc_dturbo || (sc->sc_curchan.privFlags & CHANNEL_ST))
return 6;
if (sc->sc_curchan.channelFlags & CHANNEL_2GHZ) {
/* 802.11g with short slot time */
if (ic->ic_flags & IEEE80211_F_SHSLOT)
return 9;
/* default : 802.11b or 802.11g with long slot time */
return 20;
} else if (sc->sc_curchan.channelFlags & CHANNEL_5GHZ) {
/* 802.11a/10MHz (half rates) */
if (sc->sc_curchan.channelFlags & CHANNEL_HALF)
return 13;
/* 802.11a/5MHz (quarter rates) */
if (sc->sc_curchan.channelFlags & CHANNEL_QUARTER)
return 21;
/* default : 802.11a/20MHz */
return 9;
}
/* incorrect value for channelFlags, returns a default value */
return 20;
}
static inline int
@ -4337,22 +4399,19 @@ ath_getctstimeout(struct ath_softc *sc)
}
/*
* Set the slot time based on the current setting.
* Set the slot time, ACK timeout, CTS timeout HW registers based on the
* current setting.
*/
static inline void
ath_setslottime(struct ath_softc *sc)
{
struct ieee80211com *ic = &sc->sc_ic;
struct ath_hal *ah = sc->sc_ah;
if (sc->sc_slottimeconf > 0) /* manual override */
ath_hal_setslottime(ah, sc->sc_slottimeconf);
else if (sc->sc_dturbo || (sc->sc_curchan.privFlags & CHANNEL_ST))
ath_hal_setslottime(ah, HAL_SLOT_TIME_6);
else if (ic->ic_flags & IEEE80211_F_SHSLOT)
ath_hal_setslottime(ah, HAL_SLOT_TIME_9);
else
ath_hal_setslottime(ah, HAL_SLOT_TIME_20);
ath_hal_setslottime(ah, ath_default_slottime(sc));
sc->sc_updateslot = OK;
ath_setacktimeout(sc);
ath_setctstimeout(sc);
@ -10535,18 +10594,14 @@ ath_estimate_max_distance(struct ath_softc *sc)
static inline int
ath_distance2slottime(struct ath_softc *sc, int distance)
{
/* Allowance for air propagation (roundtrip time) should be at least
* 5us per the standards.
*
* So let's set a minimum distance to accomodate this:
* roundtrip time = ((distance / speed_of_light) * 2)
* distance = ((time * 300 ) / 2) or ((5 * 300) / 2) = 750 m */
int rtdist = distance * 2;
/* IEEE 802.11-2007 10.4.3.2 defines aAirPropagationTime as being
* twice the propagation time for a signal to cross the maximum
* distance */
int c = 299; /* Speed of light in vacuum in m/us. */
/* IEEE 802.11 2007 10l.4.3.2. In us. */
int aAirPropagation = MAX(5, howmany(rtdist, c));
/* XXX: RX/TX turnaround & MAC delay. */
return ath_ccatime(sc) + aAirPropagation;
/* IEEE 802.11 2007 10.4.3.2. In us. */
int aAirPropagationTime = (distance * 2) / c;
return ath_default_slottime(sc) + aAirPropagationTime;
}
static inline int