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<div class="headertitle"><div class="title">Usage Tips</div></div>
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<div class="textblock"><p><a class="anchor" id="usage-tips"></a> </p>
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<h1><a class="anchor" id="threadsafety"></a>
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Threadsafety</h1>
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<p>This library is threadsafe. Attribues can be manipulated freely.</p>
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<h1><a class="anchor" id="do-not-delete-client-instances-unless-necessary-or-unused"></a>
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Do not delete client instances unless necessary or unused</h1>
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<p>When a client instance has been created and has connected to a peer device and it has retrieved service/characteristic information it will store that data for the life of the client instance. <br />
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If you are periodically connecting to the same devices and you have deleted the client instance or the services when connecting again it will cause a retrieval of that information from the peer again. <br />
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This results in significant energy drain on the battery of the devices, fragments heap, and reduces connection performance. <br />
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</p>
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<p>Client instances in this library use approximately 20% of the original bluedroid library, deleting them will provide much less gain than it did before. <br />
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</p>
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<p>It is recommended to retain the client instance in cases where the time between connecting to the same device is less than 5 minutes. <br />
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<br />
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<br />
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</p>
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<h1><a class="anchor" id="only-retrieve-the-services-and-characteristics-needed"></a>
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Only retrieve the services and characteristics needed</h1>
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<p>As a client the use of <code>NimBLEClient::getServices</code> or <code>NimBLERemoteService::getCharacteristics</code> and using <code>true</code> for the parameter should be limited to devices that are not known. <br />
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Instead <code>NimBLEClient::getService(NimBLEUUID)</code> or <code>NimBLERemoteService::getCharacteristic(NimBLEUUID)</code> should be used to access certain attributes that are useful to the application. <br />
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This reduces energy consumed, heap allocated, connection time and improves overall efficiency. <br />
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<br />
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<br />
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</p>
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<h1><a class="anchor" id="check-return-values"></a>
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Check return values</h1>
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<p>Many user issues can be avoided by checking if a function returned successfully, by either testing for true/false such as when calling <code>NimBLEClient::connect</code>, <br />
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or nullptr such as when calling <code>NimBLEClient::getService</code>. The latter being a must, as calling a method on a nullptr will surely result in a crash. <br />
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Most of the functions in this library return something that should be checked before proceeding. <br />
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<br />
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<br />
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</p>
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<h1><a class="anchor" id="persisted-bonds-can-be-lost-due-to-low-max_cccds"></a>
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Persisted bonds can be lost due to low MAX_CCCDS</h1>
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<p>The symptom: CONFIG_BT_NIMBLE_MAX_BONDS is set to N, but a smaller number of bonds is preserved, perhaps even a single bond. The limitation of persisted bonds can be observed via NimBLEDevice::getNumBonds(). The number may not reach CONFIG_BT_NIMBLE_MAX_BONDS.</p>
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<p>Cause: For each bond, NimBLE persists each of the CCCD (client characteristic configuration descriptor) values that have been subscribed to by the client. If CONFIG_BT_NIMBLE_MAX_CCCDS is too low, the older CCCD values are overwritten by the newer ones. The loss of the older CCCDs values results in those bonds being lost.</p>
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<p>Fix: Increase CONFIG_BT_NIMBLE_MAX_CCCDS. These take approximately 40 bytes in NVS, 2 bytes for the CCCD value and the NVS metadata overhead. The value of CONFIG_BT_NIMBLE_MAX_CCCDS should conservatively be no less than (CONFIG_BT_NIMBLE_MAX_BONDS * {maximum number of characteristics that can be subscribed to}).</p>
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<h1><a class="anchor" id="device-local-name"></a>
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Device 'Local Name'</h1>
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<p>'Local name' refers to how the device is seen and displayed.</p>
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<p>A devices 'Local name' can be thought of as coming from two places, the <em>Advertising "Local name"</em> and the <em>the GATT Device Name</em>.</p>
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<h2><a class="anchor" id="advertising-local-name"></a>
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Advertising "Local name"</h2>
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<p>Field found in the advertising data payload. Value is set via <a class="el" href="class_nim_b_l_e_advertising.html#a7fb4b74eb7acb1f46e57ff772baccd88" title="Set the advertised name of the device.">NimBLEAdvertising::setName()</a>.</p>
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<h2><a class="anchor" id="gatt-device-name"></a>
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GATT Device Name</h2>
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<p>Characteristic UUID 0x2A00 in the Generic Access service. Set via <a class="el" href="class_nim_b_l_e_device.html#a2e8bb71daabbffd9eab8787493a45ce7" title="Initialize the BLE environment.">NimBLEDevice::init()</a> or <a class="el" href="class_nim_b_l_e_device.html#aaa64b6baff54c010eb8b4d0ba338cc01" title="Set the BLEDevice name.">NimBLEDevice::setDeviceName()</a>.</p>
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<p>This characteristic is read <b>after</b> connecting to the device.</p>
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<h2><a class="anchor" id="important-considerations"></a>
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Important considerations</h2>
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<ul>
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<li>OSes cache the <em>'GATT Device Name'</em>.</li>
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<li>OSes update the device name based on the <em>'GATT Device Name'</em> after connecting to a device. This means that if you set the <em>Advertising 'Local name'</em> to "ABCD" but the <em>'GATT Device Name'</em> to "12345", the device will be seen as "ABCD" until connecting to the device, at which time the devices name will change to "12345".</li>
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<li>If no <em>'Advertising "Local name"'</em> is set, OSes, such as iOS, may display the devices name as 'Unnamed' until the device is connected to, at which time the <em>'GATT Device Name'</em> is read and used instead.</li>
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</ul>
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<p>It is recommended that both <em>'Advertising "Local name"'</em> <b>and</b> <em>'GATT Device Name'</em> be set appropriately, after considering the above described behavior.</p>
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<h1><a class="anchor" id="there-will-be-bugs---please-report-them"></a>
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There will be bugs - please report them</h1>
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<p>No code is bug free and unit testing will not find them all on it's own. If you encounter a bug, please report it along with any logs and decoded backtrace if applicable. <br />
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Best efforts will be made to correct any errors ASAP. <br />
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</p>
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<p>Bug reports can be made at <a href="https://github.com/h2zero/NimBLE-Arduino/issues">https://github.com/h2zero/NimBLE-Arduino/issues</a> or <a href="https://github.com/h2zero/esp-nimble-cpp/issues">https://github.com/h2zero/esp-nimble-cpp/issues</a>. <br />
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Questions and suggestions will be happily accepted there as well. </p>
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