Keep track of the average RSSI using an Exponential Moving Average (EMA).

Use it to dynamically tune radio receive sensitivity.

The idea is simple:
- increase sensitivity when the RSSI is bad to optimize throughput on
  long distance to the AP, and
- decrease sensitivity when the RSSI is good to reduce noise level and
  optimize throughput on short distance to the AP

The EMA allows to smooth RSSI variations so we don't end up changing the
sensitivity too frequently.  We check if it would be worth updating the
sensitivity every one second.
RSSI thresholds were taken from the Ralink Tech. Linux driver.


Also, clean a few things while I'm here:
- account for FCS when determining if RTS protection must be used
- fix check for whether WEP encryption is needed or not
- encrypt mgmt frames if we need to (shared authmode)
- cosmetic tweaks

1 files changed, 71 insertions, 37 deletions

diff --git a/sys/dev/ic/rt2661.c b/sys/dev/ic/rt2661.c
index aa78bad3cdb..5237dd00149 100644
--- a/sys/dev/ic/rt2661.c
+++ b/sys/dev/ic/rt2661.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rt2661.c,v 1.18 2006/06/01 16:24:22 robert Exp $	*/
+/*	$OpenBSD: rt2661.c,v 1.19 2006/06/08 19:58:44 damien Exp $	*/
 
 /*-
  * Copyright (c) 2006
@@ -93,7 +93,7 @@ void		rt2661_node_copy(struct ieee80211com *ic,
 int		rt2661_media_change(struct ifnet *);
 void		rt2661_next_scan(void *);
 void		rt2661_iter_func(void *, struct ieee80211_node *);
-void		rt2661_rssadapt_updatestats(void *);
+void		rt2661_updatestats(void *);
 int		rt2661_newstate(struct ieee80211com *, enum ieee80211_state,
 		    int);
 uint16_t	rt2661_eeprom_read(struct rt2661_softc *, uint8_t);
@@ -144,17 +144,18 @@ void		rt2661_read_eeprom(struct rt2661_softc *);
 int		rt2661_bbp_init(struct rt2661_softc *);
 int		rt2661_init(struct ifnet *);
 void		rt2661_stop(struct ifnet *, int);
-void		rt2661_power(int, void *);
 int		rt2661_load_microcode(struct rt2661_softc *, const uint8_t *,
 		    int);
-#ifdef notyet
 void		rt2661_rx_tune(struct rt2661_softc *);
+#ifdef notyet
 void		rt2661_radar_start(struct rt2661_softc *);
 int		rt2661_radar_stop(struct rt2661_softc *);
 #endif
 int		rt2661_prepare_beacon(struct rt2661_softc *);
 void		rt2661_enable_tsf_sync(struct rt2661_softc *);
 int		rt2661_get_rssi(struct rt2661_softc *, uint8_t);
+void		rt2661_power(int, void *);
+void		rt2661_shutdown(void *);
 
 /*
  * Supported rates for 802.11a/b/g modes (in 500Kbps unit).
@@ -344,7 +345,7 @@ rt2661_attach(void *xsc, int id)
 	sc->sc_id = id;
 
 	timeout_set(&sc->scan_ch, rt2661_next_scan, sc);
-	timeout_set(&sc->rssadapt_ch, rt2661_rssadapt_updatestats, sc);
+	timeout_set(&sc->rssadapt_ch, rt2661_updatestats, sc);
 
 	/* wait for NIC to initialize */
 	for (ntries = 0; ntries < 1000; ntries++) {
@@ -495,13 +496,16 @@ rt2661_attach(void *xsc, int id)
 	 * Make sure the interface is shutdown during reboot.
 	 */
 	sc->sc_sdhook = shutdownhook_establish(rt2661_shutdown, sc);
-	if (sc->sc_sdhook == NULL)
+	if (sc->sc_sdhook == NULL) {
 		printf("%s: WARNING: unable to establish shutdown hook\n",
 		    sc->sc_dev.dv_xname);
+	}
+
 	sc->sc_powerhook = powerhook_establish(rt2661_power, sc);
-	if (sc->sc_powerhook == NULL)
+	if (sc->sc_powerhook == NULL) {
 		printf("%s: WARNING: unable to establish power hook\n",
 		    sc->sc_dev.dv_xname);
+	}
 
 	return 0;
 
@@ -909,15 +913,24 @@ rt2661_iter_func(void *arg, struct ieee80211_node *ni)
 
 /*
  * This function is called periodically (every 100ms) in RUN state to update
- * the rate adaptation statistics.
+ * various settings like rate control statistics or Rx sensitivity.
  */
 void
-rt2661_rssadapt_updatestats(void *arg)
+rt2661_updatestats(void *arg)
 {
 	struct rt2661_softc *sc = arg;
 	struct ieee80211com *ic = &sc->sc_ic;
 
-	ieee80211_iterate_nodes(ic, rt2661_iter_func, arg);
+	if (ic->ic_opmode == IEEE80211_M_STA)
+		rt2661_iter_func(sc, ic->ic_bss);
+	else
+		ieee80211_iterate_nodes(ic, rt2661_iter_func, arg);
+
+	/* update rx sensitivity every 1 sec */
+	if (++sc->ncalls == 10) {
+		rt2661_rx_tune(sc);
+		sc->ncalls = 0;
+	}
 
 	timeout_add(&sc->rssadapt_ch, hz / 10);
 }
@@ -973,6 +986,8 @@ rt2661_newstate(struct ieee80211com *ic, enum ieee80211_state nstate, int arg)
 			rt2661_prepare_beacon(sc);
 
 		if (ic->ic_opmode != IEEE80211_M_MONITOR) {
+			sc->ncalls = 0;
+			sc->avg_rssi = -95;	/* reset EMA */
 			timeout_add(&sc->rssadapt_ch, hz / 10);
 			rt2661_enable_tsf_sync(sc);
 		}
@@ -1163,7 +1178,7 @@ rt2661_rx_intr(struct rt2661_softc *sc)
 	struct ieee80211_frame *wh;
 	struct ieee80211_node *ni;
 	struct mbuf *mnew, *m;
-	int error;
+	int error, rssi;
 
 	for (;;) {
 		desc = &sc->rxq.desc[sc->rxq.cur];
@@ -1284,8 +1299,15 @@ rt2661_rx_intr(struct rt2661_softc *sc)
 
 		/* give rssi to the rate adatation algorithm */
 		rn = (struct rt2661_node *)ni;
-		ieee80211_rssadapt_input(ic, ni, &rn->rssadapt,
-		    rt2661_get_rssi(sc, desc->rssi));
+		rssi = rt2661_get_rssi(sc, desc->rssi);
+		ieee80211_rssadapt_input(ic, ni, &rn->rssadapt, rssi);
+
+		/*-
+		 * Keep track of the average RSSI using an Exponential Moving
+		 * Average (EMA) of 8 Wilder's days:
+		 *     avg = (1 / N) x rssi + ((N - 1) / N) x avg
+		 */
+		sc->avg_rssi = (rssi + 7 * sc->avg_rssi) / 8;
 
 		/* node is no longer needed */
 		ieee80211_release_node(ic, ni);
@@ -1586,6 +1608,7 @@ rt2661_tx_mgt(struct rt2661_softc *sc, struct mbuf *m0,
     struct ieee80211_node *ni)
 {
 	struct ieee80211com *ic = &sc->sc_ic;
+	struct ifnet *ifp = &ic->ic_if;
 	struct rt2661_tx_desc *desc;
 	struct rt2661_tx_data *data;
 	struct ieee80211_frame *wh;
@@ -1599,6 +1622,17 @@ rt2661_tx_mgt(struct rt2661_softc *sc, struct mbuf *m0,
 	/* send mgt frames at the lowest available rate */
 	rate = IEEE80211_IS_CHAN_5GHZ(ni->ni_chan) ? 12 : 2;
 
+	wh = mtod(m0, struct ieee80211_frame *);
+
+	if (wh->i_fc[1] & IEEE80211_FC1_WEP) {
+		m0 = ieee80211_wep_crypt(ifp, m0, 1);
+		if (m0 == NULL)
+			return ENOBUFS;
+
+		/* packet header may have moved, reset our local pointer */
+		wh = mtod(m0, struct ieee80211_frame *);
+	}
+
 	error = bus_dmamap_load_mbuf(sc->sc_dmat, data->map, m0,
 	    BUS_DMA_NOWAIT);
 	if (error != 0) {
@@ -1630,8 +1664,6 @@ rt2661_tx_mgt(struct rt2661_softc *sc, struct mbuf *m0,
 	data->m = m0;
 	data->ni = ni;
 
-	wh = mtod(m0, struct ieee80211_frame *);
-
 	if (!IEEE80211_IS_MULTICAST(wh->i_addr1)) {
 		flags |= RT2661_TX_NEED_ACK;
 
@@ -1737,7 +1769,7 @@ rt2661_tx_data(struct rt2661_softc *sc, struct mbuf *m0,
 	if (rate == 0)
 		rate = 2;	/* fallback to 1Mbps; should not happen */
 
-	if (ic->ic_flags & IEEE80211_F_WEPON) {
+	if (wh->i_fc[1] & IEEE80211_FC1_WEP) {
 		m0 = ieee80211_wep_crypt(ifp, m0, 1);
 		if (m0 == NULL)
 			return ENOBUFS;
@@ -1752,7 +1784,7 @@ rt2661_tx_data(struct rt2661_softc *sc, struct mbuf *m0,
 	 * than the length threshold indicated by [...]" ic_rtsthreshold.
 	 */
 	if (!IEEE80211_IS_MULTICAST(wh->i_addr1) &&
-	    m0->m_pkthdr.len > ic->ic_rtsthreshold) {
+	    m0->m_pkthdr.len + IEEE80211_CRC_LEN > ic->ic_rtsthreshold) {
 		struct mbuf *m;
 		uint16_t dur;
 		int rtsrate, ackrate;
@@ -1880,7 +1912,7 @@ rt2661_tx_data(struct rt2661_softc *sc, struct mbuf *m0,
 	data->m = m0;
 	data->ni = ni;
 
-	/* remember link conditions for rate adaptation algorithm */
+	/* remember link conditions for rate control algorithm */
 	if (ic->ic_fixed_rate == -1) {
 		data->id.id_len = m0->m_pkthdr.len;
 		data->id.id_rateidx = ni->ni_txrate;
@@ -2268,6 +2300,7 @@ rt2661_select_band(struct rt2661_softc *sc, struct ieee80211_channel *c)
 		bbp17 += 0x10; bbp96 += 0x10; bbp104 += 0x10;
 	}
 
+	sc->bbp17 = bbp17;
 	rt2661_bbp_write(sc,  17, bbp17);
 	rt2661_bbp_write(sc,  96, bbp96);
 	rt2661_bbp_write(sc, 104, bbp104);
@@ -2810,7 +2843,6 @@ rt2661_load_microcode(struct rt2661_softc *sc, const uint8_t *ucode, int size)
 	return 0;
 }
 
-#ifdef notyet
 /*
  * Dynamically tune Rx sensitivity (BBP register 17) based on average RSSI and
  * false CCA count.  This function is called periodically (every seconds) when
@@ -2835,44 +2867,45 @@ rt2661_rx_tune(struct rt2661_softc *sc)
 		lo += 0x10;
 	hi = lo + 0x20;
 
+	dbm = sc->avg_rssi;
 	/* retrieve false CCA count since last call (clear on read) */
 	cca = RAL_READ(sc, RT2661_STA_CSR1) & 0xffff;
 
-	if (dbm >= -35) {
-		bbp17 = 0x60;
-	} else if (dbm >= -58) {
-		bbp17 = hi;
-	} else if (dbm >= -66) {
-		bbp17 = lo + 0x10;
-	} else if (dbm >= -74) {
-		bbp17 = lo + 0x08;
-	} else {
-		/* RSSI < -74dBm, tune using false CCA count */
+	DPRINTFN(2, ("RSSI=%ddBm false CCA=%d\n", dbm, cca));
 
+	if (dbm < -74) {
+		/* very bad RSSI, tune using false CCA count */
 		bbp17 = sc->bbp17; /* current value */
 
 		hi -= 2 * (-74 - dbm);
 		if (hi < lo)
 			hi = lo;
 
-		if (bbp17 > hi) {
+		if (bbp17 > hi)
 			bbp17 = hi;
+		else if (cca > 512)
+			bbp17 = min(bbp17 + 1, hi);
+		else if (cca < 100)
+			bbp17 = max(bbp17 - 1, lo);
 
-		} else if (cca > 512) {
-			if (++bbp17 > hi)
-				bbp17 = hi;
-		} else if (cca < 100) {
-			if (--bbp17 < lo)
-				bbp17 = lo;
-		}
+	} else if (dbm < -66) {
+		bbp17 = lo + 0x08;
+	} else if (dbm < -58) {
+		bbp17 = lo + 0x10;
+	} else if (dbm < -35) {
+		bbp17 = hi;
+	} else {	/* very good RSSI >= -35dBm */
+		bbp17 = 0x60;	/* very low sensitivity */
 	}
 
 	if (bbp17 != sc->bbp17) {
+		DPRINTF(("BBP17 %x->%x\n", sc->bbp17, bbp17));
 		rt2661_bbp_write(sc, 17, bbp17);
 		sc->bbp17 = bbp17;
 	}
 }
 
+#ifdef notyet
 /*
  * Enter/Leave radar detection mode.
  * This is for 802.11h additional regulatory domains.
@@ -3070,3 +3103,4 @@ rt2661_shutdown(void *arg)
 	
 	rt2661_stop(ifp, 1);
 }
+