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rt2x00: Fix rounding errors in RSSI average calculation 

Small changes in signal level was not detected up by the
MOVING_AVERAGE() due to a rounding error, using 'int' type.

rt2x00lib_antenna_diversity_eval:
rssi:	  -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62
rssi_avg: -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57

The signal level reported back could be significantly (5dBm)
different from the actual value. A level +3dBm is the same as
double the AP output power.

Signed-off-by: Lars Ericsson <Lars_Ericsson@telia.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Lars Ericsson 2009-08-08 23:54:51 +02:00 committed by John W. Linville
parent 193df183b1
commit 66679a65ef
2 changed files with 52 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/net/wireless/rt2x00/rt2x00.h
View File

@ -133,6 +133,17 @@
#define SHORT_EIFS ( SIFS + SHORT_DIFS + \
GET_DURATION(IEEE80211_HEADER + ACK_SIZE, 10) )
/*
* Structure for average calculation
* The avg field contains the actual average value,
* but avg_weight is internally used during calculations
* to prevent rounding errors.
*/
struct avg_val {
int avg;
int avg_weight;
};
/*
* Chipset identification
* The chipset on the device is composed of a RT and RF chip.
@ -256,7 +267,7 @@ struct link_ant {
* Similar to the avg_rssi in the link_qual structure
* this value is updated by using the walking average.
*/
int rssi_ant;
struct avg_val rssi_ant;
};
/*
@ -285,7 +296,7 @@ struct link {
/*
* Currently active average RSSI value
*/
int avg_rssi;
struct avg_val avg_rssi;
/*
* Currently precalculated percentages of successful

65
drivers/net/wireless/rt2x00/rt2x00link.c
View File

@ -46,7 +46,15 @@
#define DEFAULT_PERCENTAGE 50
/*
* Small helper macro to work with moving/walking averages.
* Small helper macro for percentage calculation
* This is a very simple macro with the only catch that it will
* produce a default value in case no total value was provided.
*/
#define PERCENTAGE(__value, __total) \
( (__total) ? (((__value) * 100) / (__total)) : (DEFAULT_PERCENTAGE) )
/*
* Helper struct and macro to work with moving/walking averages.
* When adding a value to the average value the following calculation
* is needed:
*
@ -60,18 +68,28 @@
* for a few minutes but when the device is moved away from the AP
* the average will not decrease fast enough to compensate.
* The walking average compensates this and will move towards
* the new values correctly allowing a effective link tuning.
* the new values correctly allowing a effective link tuning,
* the speed of the average moving towards other values depends
* on the value for the number of samples. The higher the number
* of samples, the slower the average will move.
* We use two variables to keep track of the average value to
* compensate for the rounding errors. This can be a significant
* error (>5dBm) if the factor is too low.
*/
#define MOVING_AVERAGE(__avg, __val, __samples) \
( (((__avg) * ((__samples) - 1)) + (__val)) / (__samples) )
/*
* Small helper macro for percentage calculation
* This is a very simple macro with the only catch that it will
* produce a default value in case no total value was provided.
*/
#define PERCENTAGE(__value, __total) \
( (__total) ? (((__value) * 100) / (__total)) : (DEFAULT_PERCENTAGE) )
#define AVG_SAMPLES 8
#define AVG_FACTOR 1000
#define MOVING_AVERAGE(__avg, __val) \
({ \
struct avg_val __new; \
__new.avg_weight = \
(__avg).avg_weight ? \
((((__avg).avg_weight * ((AVG_SAMPLES) - 1)) + \
((__val) * (AVG_FACTOR))) / \
(AVG_SAMPLES) ) : \
((__val) * (AVG_FACTOR)); \
__new.avg = __new.avg_weight / (AVG_FACTOR); \
__new; \
})
/*
* For calculating the Signal quality we have determined
@ -98,8 +116,8 @@ static int rt2x00link_antenna_get_link_rssi(struct rt2x00_dev *rt2x00dev)
{
struct link_ant *ant = &rt2x00dev->link.ant;
if (ant->rssi_ant && rt2x00dev->link.qual.rx_success)
return ant->rssi_ant;
if (ant->rssi_ant.avg && rt2x00dev->link.qual.rx_success)
return ant->rssi_ant.avg;
return DEFAULT_RSSI;
}
@ -121,7 +139,8 @@ static void rt2x00link_antenna_update_rssi_history(struct rt2x00_dev *rt2x00dev,
static void rt2x00link_antenna_reset(struct rt2x00_dev *rt2x00dev)
{
rt2x00dev->link.ant.rssi_ant = 0;
rt2x00dev->link.ant.rssi_ant.avg = 0;
rt2x00dev->link.ant.rssi_ant.avg_weight = 0;
}
static void rt2x00lib_antenna_diversity_sample(struct rt2x00_dev *rt2x00dev)
@ -258,8 +277,6 @@ void rt2x00link_update_stats(struct rt2x00_dev *rt2x00dev,
struct link_qual *qual = &rt2x00dev->link.qual;
struct link_ant *ant = &rt2x00dev->link.ant;
struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
int avg_rssi = rxdesc->rssi;
int ant_rssi = rxdesc->rssi;
/*
* Frame was received successfully since non-succesfull
@ -279,16 +296,12 @@ void rt2x00link_update_stats(struct rt2x00_dev *rt2x00dev,
/*
* Update global RSSI
*/
if (link->avg_rssi)
avg_rssi = MOVING_AVERAGE(link->avg_rssi, rxdesc->rssi, 8);
link->avg_rssi = avg_rssi;
link->avg_rssi = MOVING_AVERAGE(link->avg_rssi, rxdesc->rssi);
/*
* Update antenna RSSI
*/
if (ant->rssi_ant)
ant_rssi = MOVING_AVERAGE(ant->rssi_ant, rxdesc->rssi, 8);
ant->rssi_ant = ant_rssi;
ant->rssi_ant = MOVING_AVERAGE(ant->rssi_ant, rxdesc->rssi);
}
static void rt2x00link_precalculate_signal(struct rt2x00_dev *rt2x00dev)
@ -421,10 +434,10 @@ static void rt2x00link_tuner(struct work_struct *work)
* collect the RSSI data we could use this. Otherwise we
* must fallback to the default RSSI value.
*/
if (!link->avg_rssi || !qual->rx_success)
if (!link->avg_rssi.avg || !qual->rx_success)
qual->rssi = DEFAULT_RSSI;
else
qual->rssi = link->avg_rssi;
qual->rssi = link->avg_rssi.avg;
/*
* Only perform the link tuning when Link tuning
@ -442,7 +455,7 @@ static void rt2x00link_tuner(struct work_struct *work)
/*
* Send a signal to the led to update the led signal strength.
*/
rt2x00leds_led_quality(rt2x00dev, link->avg_rssi);
rt2x00leds_led_quality(rt2x00dev, qual->rssi);
/*
* Evaluate antenna setup, make this the last step when