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en:users:drivers:ath9k:spectral_scan [2015/01/26 09:49]
127.0.0.1 external edit
en:users:drivers:ath9k:spectral_scan [2017/01/09 19:47] (current)
Adam Hunt Added 'speccy' to list of spectral scan tools
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- +===== ath9k spectral scan =====
-===== ath9k spectral scan=====+
  
 Atheros 802.11n chipsets include a built-in spectral analysis feature. AR92xx and AR93xx have the ability to report FFT data from the baseband under software controlled conditions, including: ​ Atheros 802.11n chipsets include a built-in spectral analysis feature. AR92xx and AR93xx have the ability to report FFT data from the baseband under software controlled conditions, including: ​
   * absolute magnitude (|i|+|q|, abs() for I/Q phase of the wireless signal) for each FFT bin (56 for subcarriers in HT20 mode and 128 in HT40 mode)    * absolute magnitude (|i|+|q|, abs() for I/Q phase of the wireless signal) for each FFT bin (56 for subcarriers in HT20 mode and 128 in HT40 mode) 
   * an index indicating the strongest FFT bin    * an index indicating the strongest FFT bin 
-  * the maximum signal magnitude for each sample ​These information can be used to create an open source spectrum analyzer or interference classifier ​+  * the maximum signal magnitude for each sample
  
-To try it out, you can use the following commands to acquire samples for all channels which can be scanned: ​+These information can be used to create an open source spectrum analyzer or interference classifier. ​To try it out, you can use the following commands to acquire samples for all channels which can be scanned: ​
  
  
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 cat /​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/​spectral_scan0 > samples cat /​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/​spectral_scan0 > samples
 echo disable > /​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/​spectral_scan_ctl</​code>​ echo disable > /​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/​spectral_scan_ctl</​code>​
-Spectral scan configuration parameters can be read and changed /​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/:​  +Spectral scan configuration parameters can be read and changed ​''​/​sys/​kernel/​debug/​ieee80211/​phy0/​ath9k/​''​
-    * spectral_count:​ number of scan results requested. Note that the "never disable"​ mode is implemented through the "​background"​ mode in specral_scan_ctl,​ see below.  + 
-    * spectral_short_repeat:​ controls the short_repeat parameter, see "​Spectral scan parameters"​ below  +  * **spectral_count**: number of scan results requested. Note that the "never disable"​ mode is implemented through the "​background"​ mode in specral_scan_ctl,​ see below.  
-    * spectral_fft_period:​ controls the fft_period parameter, see "​Spectral scan parameters"​ below  +  * **spectral_short_repeat**: controls the short_repeat parameter, see "​Spectral scan parameters"​ below  
-    * spectral_period:​ controls the period parameter, see "​Spectral scan parameters"​ below  +  * **spectral_fft_period**: controls the //fft_period// parameter, see "​Spectral scan parameters"​ below  
-    * spectral_scan_ctl:​ Contains the current mode. There are the following modes available:  +  * **spectral_period**: controls the //period// parameter, see "​Spectral scan parameters"​ below  
-    *  ​* ​disable: spectral scan is disabled  +  * **spectral_scan_ctl**: Contains the current mode. There are the following modes available:  
-    *  ​* ​background: spectral scans samples are returned endlessly from the currently configured channel. It is running while the hardware is not busy with sending/​receiving. Must be turned on by writing "​trigger"​ into spectral_scan_ctl.  +    * ''​disable''​: spectral scan is disabled  
-    *  ​* ​manual: as many spectral scan samples as configured in spectral_count are returned from the current channel after writing "​trigger"​ into spectral_scan_ctl.  +    * ''​background''​: spectral scans samples are returned endlessly from the currently configured channel. It is running while the hardware is not busy with sending/​receiving. Must be turned on by writing "​trigger"​ into spectral_scan_ctl.  
-    *  ​* ​chanscan: as many spectral scan samples as configured in spectral_count are returned for each channel when performing a scan.  +    * ''​manual''​: as many spectral scan samples as configured in spectral_count are returned from the current channel after writing "​trigger"​ into spectral_scan_ctl.  
-    *   ​spectral_scan0:​ the relayfs file which returns the spectral scan samples. The samples are returned as TLV binary data, see drivers/​net/​wireless/​ath/​ath9k/​spectral.h and/or drivers/​net/​wireless/​ath/​spectral_common.h for the format  +    * ''​chanscan''​: as many spectral scan samples as configured in spectral_count are returned for each channel when performing a scan.  
-===== Spectral scan parameters===== +  *   **spectral_scan0**: the relayfs file which returns the spectral scan samples. The samples are returned as TLV binary data, see ''​drivers/​net/​wireless/​ath/​ath9k/​spectral.h'' ​and/​or ​''​drivers/​net/​wireless/​ath/​spectral_common.h'' ​for the format ​ 
-    ​* ​  * fft_period: when active and triggered, PHY passes FFT frames to MAC every (fft_period+1)*4uS  + 
-    ​* ​  * period: when active, time period between successive spectral scan entry points (period*256*Tclk). Tclk = 44MHz for HT20 operation, 88MHz for HT40 operation  +===== Spectral scan parameters ===== 
-    ​* ​  * count: number of scan results requested. There are special meanings in some chip revisions:  +  //fft_period//: when active and triggered, PHY passes FFT frames to MAC every (fft_period+1)*4uS  
-    ​*   ​*  ​* AR92xx: highest bit set (>=128) is interpreted as "never disable"​  +  //period//: when active, time period between successive spectral scan entry points (period*256*Tclk). Tclk = 44MHz for HT20 operation, 88MHz for HT40 operation  
-    ​*   ​*  ​* AR9300 and newer: 0 is interpreted as "never disable"​  +  //count//: number of scan results requested. There are special meanings in some chip revisions:  
-      *   short_repeat:​ controls whether the chip is in spectral scan mode for 4 usec (enabled) or 204 usec (disabled)  +    * AR92xx: highest bit set (>=128) is interpreted as "never disable"​  
-===== Frame format===== +    * AR9300 and newer: 0 is interpreted as "never disable"​  
-    ​* ​  ​* ​  ​* ​HT20 +  //short_repeat//: controls whether the chip is in spectral scan mode for 4 usec (enabled) or 204 usec (disabled) 
 + 
 +===== Frame format ===== 
 +HT20:
 <​code> ​     0       ​1 ​      ​2 ​      ​3 ​      ​4 ​      ​5 ​      ​6 ​      ​7 ​      8 <​code> ​     0       ​1 ​      ​2 ​      ​3 ​      ​4 ​      ​5 ​      ​6 ​      ​7 ​      8
       +---------------------------------------------------------------+       +---------------------------------------------------------------+
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  ​59 ​  ​| ​                      [3:0] max_exp ​                          |  ​59 ​  ​| ​                      [3:0] max_exp ​                          |
       +---------------------------------------------------------------+</​code>​       +---------------------------------------------------------------+</​code>​
-    *   ​* ​    ​* ​HT40 + 
 +HT40:
 <​code> ​     0       ​1 ​      ​2 ​      ​3 ​      ​4 ​      ​5 ​      ​6 ​      ​7 ​      8 <​code> ​     0       ​1 ​      ​2 ​      ​3 ​      ​4 ​      ​5 ​      ​6 ​      ​7 ​      8
       +---------------------------------------------------------------+       +---------------------------------------------------------------+
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       +---------------------------------------------------------------+</​code>​       +---------------------------------------------------------------+</​code>​
  
-===== Riceved ​power computation=====+===== Received ​power computation =====
  
 Assuming the noise floor is equal to -96dbm(*) and the magnitude of each sample in a 20MHz bin equals the RSSI, the received signal strength of each FFT bin on HT20 channel can be computed as follow: ​ Assuming the noise floor is equal to -96dbm(*) and the magnitude of each sample in a 20MHz bin equals the RSSI, the received signal strength of each FFT bin on HT20 channel can be computed as follow: ​
-    *   ​* ​      ​* ​power(i) = nf + RSSI + 10*log(b(i)^2) - bin_sum where:  +<​code>​ 
-    ​* ​  ​* ​        * RSSI is computed on control chain 0  +power(i) = nf + RSSI + 10*log(b(i)^2) - bin_sum 
-    ​* ​  ​* ​        * b(i) is the magnitude in each bin, unscaled by max_exp  +</​code>​ 
-    ​* ​  ​* ​        * bin_sum = 10*log(sum[i=1..56](b(i)^2)) For 40MHz channel, previous formula should be used for 64 bins of control and extension channels, keeping in mind for HT40+ mode the extension channel is above the primary one (lower=ctl, upper=ext) and for HT40- the extension channel is below the primary one (lower=ext, upper=ctl) ​+where:  
 +  //RSSI// is computed on control chain 0  
 +  //b(i)// is the magnitude in each bin, unscaled by //max_exp// 
 +  //bin_sum// = 10*log(sum[i=1..56](b(i)^2)) 
 + 
 +For 40MHz channel, previous formula should be used for 64 bins of control and extension channels, keeping in mind for HT40+ mode the extension channel is above the primary one (lower=ctl, upper=ext) and for HT40- the extension channel is below the primary one (lower=ext, upper=ctl).
  
-(*) nf can differ from -96dbm due to noise and spikes leading to a reduced reported RSSI +(*) nf can differ from -96dbm due to noise and spikes leading to a reduced reported RSSI.
  
  
-===== Userspace programs=====+===== Userspace programs =====
  
 FFT samples gathered from Atheros NICs could be drawn using userspace programs: ​ FFT samples gathered from Atheros NICs could be drawn using userspace programs: ​
-    *   ​*           * [[https://​github.com/​simonwunderlich/​FFT_eval|https://​github.com/​simonwunderlich/​FFT_eval]] (HT20 only)  +  * [[https://​github.com/​simonwunderlich/​FFT_eval|https://​github.com/​simonwunderlich/​FFT_eval]] (HT20 only)  
-    ​* ​  ​* ​          * [[https://​github.com/​LorenzoBianconi/​ath_spectral|https://​github.com/​LorenzoBianconi/​ath_spectral]] ​+  * [[https://​github.com/​LorenzoBianconi/​ath_spectral|https://​github.com/​LorenzoBianconi/​ath_spectral]]  
 +  * [[https://​github.com/​bcopeland/​speccy|https://​github.com/​bcopeland/​speccy]]
  
 (based on Adrian Chadd'​s documentation [[https://​wiki.freebsd.org/​dev/​ath_hal(4)/​SpectralScan|https://​wiki.freebsd.org/​dev/​ath_hal%284%29/​SpectralScan]]) ​ (based on Adrian Chadd'​s documentation [[https://​wiki.freebsd.org/​dev/​ath_hal(4)/​SpectralScan|https://​wiki.freebsd.org/​dev/​ath_hal%284%29/​SpectralScan]]) ​
  
en/users/drivers/ath9k/spectral_scan.1422265793.txt.gz · Last modified: 2016/12/23 10:54 (external edit)