1 /*
2  * Copyright (C) 2019 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package com.android.server.wifi.util;
17 
18 import android.annotation.NonNull;
19 import android.content.Context;
20 import android.net.wifi.WifiInfo;
21 
22 import com.android.wifi.resources.R;
23 
24 /** Utilities for computations involving RSSI. */
25 public class RssiUtil {
RssiUtil()26     private RssiUtil() {}
27 
28     /**
29      * Apply known fixes to a RSSi from signal poll and return INVALID_RSSI to indicate the data
30      * is invalid.
31      */
calculateAdjustedRssi(int rssi)32     public static int calculateAdjustedRssi(int rssi) {
33         if (rssi > WifiInfo.INVALID_RSSI && rssi < WifiInfo.MAX_RSSI) {
34             /*
35              * Positive RSSI is possible when devices are close(~0m apart) to each other.
36              * And there are some driver/firmware implementation, where they avoid
37              * reporting large negative rssi values by adding 256.
38              * so adjust the valid rssi reports for such implementations.
39              */
40             if (rssi > (WifiInfo.INVALID_RSSI + 256)) {
41                 return rssi - 256;
42             }
43             return rssi;
44         }
45         return WifiInfo.INVALID_RSSI;
46     }
47 
48     /** Calculate RSSI level from RSSI using overlaid RSSI level thresholds. */
calculateSignalLevel(Context context, int rssi)49     public static int calculateSignalLevel(Context context, int rssi) {
50         int[] thresholds = getRssiLevelThresholds(context);
51 
52         for (int level = 0; level < thresholds.length; level++) {
53             if (rssi < thresholds[level]) {
54                 return level;
55             }
56         }
57         return thresholds.length;
58     }
59 
60     @NonNull
getRssiLevelThresholds(Context context)61     private static int[] getRssiLevelThresholds(Context context) {
62         // getIntArray() will never return null, it will throw instead
63         return context.getResources().getIntArray(R.array.config_wifiRssiLevelThresholds);
64     }
65 }
66