Android AOSP - Definition of scan interval and sca

问题:

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.

回答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.

回答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;