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I have already found some guide related to this. But my experience is that if wifi.supplicant_scan_interval = 15
my device scans for wifi with 60s period so I dont think that this is the right parameter for that. Any suggestions?
Edited: here is my build.prop:

# begin build properties
# autogenerated by buildinfo.sh
ro.build.id=GRK39F
ro.build.display.id=GRK39F
ro.build.version.incremental=eng.paul.30092011.041430
ro.build.version.sdk=10
ro.build.version.codename=REL
ro.build.version.release=2.3.6
ro.build.date=Fri Aug 30 04:14:55 EDT 2011
ro.build.date.utc=0
ro.build.type=user
ro.build.user=paul
ro.build.host=paul-VM
ro.build.tags=test-keys
ro.product.model=U20i
ro.product.brand=Sony Ericsson
ro.product.name=mimmi
ro.product.device=mimmi
ro.product.board=mimmi
ro.product.cpu.abi=armeabi-v6l
ro.product.cpu.abi2=armeabi
ro.product.manufacturer=Sony Ericsson
ro.product.locale.language=en
ro.product.locale.region=US
ro.wifi.channels=14
ro.board.platform=msm7k
# ro.build.product is obsolete; use ro.product.device
ro.build.product=mimmi
# Do not try to parse ro.build.description or .fingerprint
ro.build.description=passion-user 2.3.6 GRK39F 189904 release-keys
ro.build.fingerprint=google/passion/passion:2.3.6/GRK39F/189904:user/release-keys
# end build properties

#
# ADDITIONAL_BUILD_PROPERTIES
#
keyguard.no_require_sim=true
ro.ril.hsxpa=2
ro.ril.hsupa.category=5
ro.ril.def.agps.mode=2
ro.media.dec.jpeg.memcap=20000000
rild.libpath=/system/lib/libril-qc-1.so
rild.libargs=-d /dev/smd0
wifi.interface=wlan0
wifi.supplicant_scan_interval=15
ro.ril.def.agps.mode=2
ro.ril.def.agps.feature=1
ro.opengles.version=131072
ro.com.google.locationfeatures=1
ro.com.google.networklocation=1
ro.ril.enable.a52=1
ro.ril.enable.a53=1
ro.media.enc.file.format=3gp,mp4
ro.media.enc.vid.codec=m4v,h263
ro.media.enc.vid.h263.width=176,640
ro.media.enc.vid.h263.height=144,480
ro.media.enc.vid.h263.bps=64000,1600000
ro.media.enc.vid.h263.fps=1,30
ro.media.enc.vid.m4v.width=176,640
ro.media.enc.vid.m4v.height=144,480
ro.media.enc.vid.m4v.bps=64000,1600000
ro.media.enc.vid.m4v.fps=1,30
ro.media.dec.aud.wma.enabled=1
ro.media.dec.vid.wmv.enabled=1
ro.media.dec.aud.divx.enabled=1
ro.media.dec.vid.xvid.enabled=1
settings.display.autobacklight=0
media.stagefright.enable-player=true
media.stagefright.enable-meta=true
media.stagefright.enable-scan=true
media.stagefright.enable-http=true
keyguard.no_require_sim=true

#MT and LCD
ro.sf.lcd_density=120
qemu.sf.lcd_density=120
ro.product.multi_touch_enabled=true
ro.product.max_max_num_touch=2

dalvik.vm.execution-mode=int:jit
dalvik.vm.heapsize=32m
ro.compcache.default=0
ro.rommanager.developerid=cyanogenmod
ro.url.legal=http://www.google.com/intl/%s/mobile/android/basic/phone-legal.html
ro.url.legal.android_privacy=http://www.google.com/intl/%s/mobile/android/basic/privacy.html
ro.com.google.clientidbase=android-sonyericsson
ro.com.android.wifi-watchlist=GoogleGuest
ro.setupwizard.enterprise_mode=1
ro.com.android.dateformat=MM-dd-yyyy
ro.com.android.dataroaming=false
ro.config.ringtone=MiniCM7Pro.mp3
ro.config.notification_sound=DontPanic.ogg
ro.config.alarm_alert=alarm.ogg
ro.modversion=MiniCM7 Pro V16 Pre-Final
ro.setupwizard.mode=OPTIONAL
net.bt.name=Android
dalvik.vm.stack-trace-file=/data/anr/traces.txt

#SEMC
persist.service.xloud.enable=1
persist.service.swiqi.enable=1
ro.semc.timescape_keys=Sony_Ericsson_Xperia
ro.semc.sound_effects_enabled=true
ro.semc.xloud.supported=true
ro.service.swiqi.supported=true
ro.semc.batt.capacity=950
ro.semc.batt.test.consumption=150
ro.semc.batt.test.z_threshold=50
ro.semc.batt.test.min_level=60

Edit2: The scanning period is depending on the connectivity as well. Means if the phone establishes a WI-FI connection, then the scanning period will be different from the wifi.supplicant_scan_interval. Also when the phone get into idle state (around 10 mins of inactivity) the scanning period will be 10 min.

share|improve this question
    
Look at post #4 of that guide you have enclosed in your question. –  t0mm13b Jan 14 '13 at 16:10
    
Have I missed something else not mentioned in my question? –  laplasz Jan 14 '13 at 20:16
    
Are you rooted? Do you have access to /system as rw? Can you paste in the full contents of build.prop into this? Does your Wifi driver have the capability to set the scan interval via build.prop? Also, point to remember, 60seconds is better and less taxing on the battery instead of 15seconds! –  t0mm13b Jan 14 '13 at 20:19
    
@t0mm13b yes, the phone is rooted, build.prop is added. Actually I am writing an app using wifi, and i measured the scan period which was 60s. Yes it better then 15, but I would like to know where this 60s comes from. thanks –  laplasz Jan 14 '13 at 21:25

1 Answer 1

up vote 1 down vote accepted

This property comes from during build-time and is extremely, dependant on the wifi driver, for each and every device tree that gets integrated into the build of Android, there's what's called an overlay, this overlay may contain extras pertaining to the said device in question.

In fact, its rather, an XML document that gets parsed during build and "overlays" or "overwrites" the standard Android defaults, such as animation speed, etc.

This pertinent information of this comes from the device's overlay/frameworks/base/core/res/res/values/config.xml which contains the very exact line:

<!-- Boolean indicating whether the wifi chipset has background scan support -->
<bool translatable="false" name="config_wifi_background_scan_support">true</bool>

From that, that is telling the build, to say, that the property wifi.supplicant_scan_interval is supported and can be used dynamically from the build.prop file found in the /system directory, which in turn, is read from the Android's native binary executable wpa_supplicant.

However, it must be said, it depends on the Wifi Driver to support that, and how much integration of the Wifi functionality is within the frameworks. To find the exact source can be found in external/wpa_supplicant/wpa_supplicant.c, around lines 2459:

#ifdef ANDROID
    char scan_prop[PROPERTY_VALUE_MAX];
    char *endp;
    if (property_get("wifi.supplicant_scan_interval", scan_prop, "5") != 0) {
        wpa_s->scan_interval = (int)strtol(scan_prop, &endp, 0);
        if (endp == scan_prop) {
            wpa_s->scan_interval = 5;
        }
    }
#endif

default here on Gingerbread is 5secs, again the mileage will vary depending on the version of wpa_supplicant used, there was two versions, wpa_supplicant_6 which was broken under ICS, and the newer version wpa_supplicant_8, despite saying that, it may no longer be supported now with the newer releases.

share|improve this answer
    
Thanks for the detailed answer! However I cannot find these files your are mentioning: so what is the exact path to the .c file, and .xml? I am using Root explorer, but no overlay/ and no external/ folder in root –  laplasz Jan 15 '13 at 20:10
    
It is in the AOSP source code, you are not going to find it in Android ROM that you have currently in your handset, the details mentioned above would be if and when the AOSP source gets pulled down to your machine prior to building Android. –  t0mm13b Jan 15 '13 at 20:33
    
So what I understand is that Wifi scan period time can be 60s even wifi.supplicant_scan_interval = 15. And I cannot check it, just measure the exact time? –  laplasz Jan 15 '13 at 20:37
1  
If the build.prop has that property in place but does not actually scan for that specified period, the binary executable in Android, wpa_supplicant is not patched in to have the capability to read that property from build.prop. BTW to make it clear, its stated build-time meaning before compiling Android which is what my answer is pointing out. –  t0mm13b Jan 15 '13 at 20:45
1  
Assuming the binary is not patched in, then you cannot modify it. –  t0mm13b Jan 15 '13 at 21:34

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