Android AOSP - Definition of scan interval and scan window in android source code

Question

I have downloaded the AOSP Source code for Lollipop 5.0. In api level 21, under bluetooth low energy scan settings there are three options for scanning the ble devices- SCAN_MODE_BALANCED, SCAN_MODE_LOW_LATENCY, SCAN_MODE_LOW_POWER. Are the based on different scan interval and scan window values? If so, where can I find the values defined for these macros in the source code directory.

Aldis

Answer 1

I found below values in http://androidxref.com/5.0.0_r2/xref/packages/apps/Bluetooth/src/com/android/bluetooth/gatt/ScanManager.java while greping the keyword "SCAN_MODE_BALANCED" :

    /**
     * Scan params corresponding to regular scan setting
     */
    private static final int SCAN_MODE_LOW_POWER_WINDOW_MS = 500;
    private static final int SCAN_MODE_LOW_POWER_INTERVAL_MS = 5000;
    private static final int SCAN_MODE_BALANCED_WINDOW_MS = 2000;
    private static final int SCAN_MODE_BALANCED_INTERVAL_MS = 5000;
    private static final int SCAN_MODE_LOW_LATENCY_WINDOW_MS = 5000;
    private static final int SCAN_MODE_LOW_LATENCY_INTERVAL_MS = 5000;

    /**
     * Scan params corresponding to batch scan setting
     */
    private static final int SCAN_MODE_BATCH_LOW_POWER_WINDOW_MS = 1500;
    private static final int SCAN_MODE_BATCH_LOW_POWER_INTERVAL_MS = 150000;
    private static final int SCAN_MODE_BATCH_BALANCED_WINDOW_MS = 1500;
    private static final int SCAN_MODE_BATCH_BALANCED_INTERVAL_MS = 15000;
    private static final int SCAN_MODE_BATCH_LOW_LATENCY_WINDOW_MS = 1500;
    private static final int SCAN_MODE_BATCH_LOW_LATENCY_INTERVAL_MS = 5000;

Also checkout out ScanManager.ScanNative.configureRegularScanParams(). Two params scanWindow and scanInterval are set according to the scan setting (ScanSettings.SCAN_MODE_LOW_POWER, ScanSettings.SCAN_MODE_BALANCED, ScanSettings.SCAN_MODE_LOW_LATENCY), converted into BLE units, and then passed to gattSetScanParametersNative().

Hope this helps.

Swigart

What does it exactly mean if I say I set my ScanSettings to SCAN_MODE_LOW_LATENCY ? Does it say it scans every 5 seconds for 5 seconds and then starts scanning again - I don't think this is the case as I have an application where the updates are faster than every 5 second. Could you please elaborate on interpreting these values? – Piotrowski

Answer 2

I'm not sure if this is accurate or if you can even use it to find the values you need, but I found some code from Google regarding scanning settings:

  // Constants for Scan Cycle
  // Low Power: 2.5 minute period with 1.5 seconds active (1% duty cycle)
  /* @VisibleForTesting */ static final int LOW_POWER_IDLE_MILLIS = 148500;
  /* @VisibleForTesting */ static final int LOW_POWER_ACTIVE_MILLIS = 1500;

  // Balanced: 15 second period with 1.5 second active (10% duty cycle)
  /* @VisibleForTesting */ static final int BALANCED_IDLE_MILLIS = 13500;
  /* @VisibleForTesting */ static final int BALANCED_ACTIVE_MILLIS = 1500;

  // Low Latency: 1.67 second period with 1.5 seconds active (90% duty cycle)
  /* @VisibleForTesting */ static final int LOW_LATENCY_IDLE_MILLIS = 167;
  /* @VisibleForTesting */ static final int LOW_LATENCY_ACTIVE_MILLIS = 1500;

Busiek

Thankyou Tim. But i couldnt find such kind of definitions in google android source code .After searching in driver level i found something here like this androidxref.com/5.0.0_r2/xref/external/bluetooth/bluedroid/… #define BTM_BLE_GAP_DISC_SCAN_INT 18 /* Interval(scan_int) = 11.25 ms= 0x0010 * 0.625 ms / #define BTM_BLE_GAP_DISC_SCAN_WIN 18 / scan_window = 11.25 ms= 0x0010 * 0.625 ms */ – Aldis

is the above corresponds to the scan window and scan interval .But i wonder how they define the values for SCAN_MODE_BALANCED, SCAN_MODE_LOW_LATENCY, SCAN_MODE_LOW_POWER ! – Aldis