| <!DOCTYPE html> |
| <html lang="en"> |
| <head> |
| <meta charset="utf-8"> |
| <meta http-equiv="X-UA-Compatible" content="IE=edge"> |
| <meta name="viewport" content="width=device-width, initial-scale=1.0"> |
| |
| |
| <!-- This is broken by doc revisioning. |
| --> |
| <link rel="shortcut icon" href="../../../../img/favicon.ico"> |
| |
| <title>Characteristic Access - Apache Mynewt</title> |
| |
| <link href="../../../../css/bootstrap-3.0.3.min.css" rel="stylesheet"> |
| <link rel="stylesheet" href="../../../../css/highlight.css"> |
| <link href="../../../../css/base.css" rel="stylesheet"> |
| <link href="../../../../css/custom.css" rel="stylesheet"> |
| <link href="../../../../css/v2.css" rel="stylesheet"> |
| <link href="https://fonts.googleapis.com/css?family=Lato" rel="stylesheet"> |
| <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css"> |
| |
| <!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries --> |
| <!--[if lt IE 9]> |
| <script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script> |
| <script src="https://oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script> |
| <![endif]--> |
| |
| |
| <script> |
| (function(i, s, o, g, r, a, m) { |
| i["GoogleAnalyticsObject"] = r; |
| (i[r] = |
| i[r] || |
| function() { |
| (i[r].q = i[r].q || []).push(arguments); |
| }), |
| (i[r].l = 1 * new Date()); |
| (a = s.createElement(o)), (m = s.getElementsByTagName(o)[0]); |
| a.async = 1; |
| a.src = g; |
| m.parentNode.insertBefore(a, m); |
| })(window, document, "script", "//www.google-analytics.com/analytics.js", "ga"); |
| |
| ga("create", "UA-72162311-1", "auto"); |
| ga("send", "pageview"); |
| </script> |
| |
| </head> |
| |
| |
| <body class="Characteristic Access"> |
| |
| |
| <div class="container"> |
| <div class="row v2-main-banner"> |
| <a class="logo-cell" href="/"> |
| <img class="logo" src="/img/logo.png"> |
| </a> |
| <div class="tagline-cell"> |
| <h4 class="tagline">An OS to build, deploy and securely manage billions of devices</h4> |
| </div> |
| <div class="news-cell"> |
| <div class="well"> |
| <h4>Latest News:</h4> <a href="/download">Apache Mynewt 1.12.0, Apache NimBLE 1.7.0 </a> released (April 4, 2024) |
| </div> |
| </div> |
| </div> |
| </div> |
| |
| |
| |
| |
| |
| |
| |
| |
| <nav id="navbar" class="navbar navbar-inverse affix-top" data-spy="affix" data-offset-top="150" role="navigation"> |
| <div class="container"> |
| <!-- Collapsed navigation --> |
| <div class="navbar-header"> |
| <!-- Expander button --> |
| <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse"> |
| <span class="sr-only">Toggle navigation</span> |
| <span class="icon-bar"></span> |
| <span class="icon-bar"></span> |
| <span class="icon-bar"></span> |
| </button> |
| |
| </div> |
| |
| <!-- Expanded navigation --> |
| <div class="navbar-collapse collapse"> |
| <!-- Main navigation --> |
| <ul class="nav navbar-nav navbar-right"> |
| <li |
| class="" |
| > |
| <a href="/"><i class="fa fa-home" style="font-size: larger;"></i></a> |
| </li> |
| <li |
| class="important" |
| > |
| <a href="/quick-start/">Quick Start</a> |
| </li> |
| <li |
| class="" |
| > |
| <a href="/about/">About</a> |
| </li> |
| <li |
| class="" |
| > |
| <a href="/talks/">Talks</a> |
| </li> |
| <li |
| class="active" |
| > |
| <a href="/documentation/">Documentation</a> |
| </li> |
| <li |
| class="" |
| > |
| <a href="/download/">Download</a> |
| </li> |
| <li |
| class="" |
| > |
| <a href="/community/">Community</a> |
| </li> |
| <li |
| class="" |
| > |
| <a href="/events/">Events</a> |
| </li> |
| </ul> |
| |
| </div> |
| </div> |
| </nav> |
| |
| |
| |
| <div class="container"> |
| |
| <div class="row"> |
| <div class="col-md-3 v2-sidebar sidebar-container"><div id="docSidebar" class="hidden-print" role="complementary"> |
| <div class="top"> |
| <div role="search"> |
| <form id="rtd-search-form" class="wy-form" action="../../../../search.html" method="get"> |
| <div class="form-group"> |
| <input type="text" name="q" class="form-control" placeholder="Search documentation" /> |
| </div> |
| </form> |
| </div> |
| </div> |
| <ul class="toc-nav"> |
| <li class="doc-version"><select class="form-control" onchange="if (this.value) window.location.href=this.value"> |
| <option value="/latest"> |
| Version: master |
| </option> |
| <option value="/v1_12_0/" > |
| Version: 1.12.0 |
| </option> |
| <option value="/v1_11_0/" > |
| Version: 1.11.0 |
| </option> |
| <option value="/v1_10_0/" > |
| Version: 1.10.0 |
| </option> |
| <option value="/v1_9_0/" > |
| Version: 1.9.0 |
| </option> |
| <option value="/v1_8_0/" > |
| Version: 1.8.0 |
| </option> |
| <option value="/v1_7_0/" > |
| Version: 1.7.0 |
| </option> |
| <option value="/v1_6_0/" > |
| Version: 1.6.0 |
| </option> |
| <option value="/v1_5_0/" > |
| Version: 1.5.0 |
| </option> |
| <option value="/v1_4_0/" > |
| Version: 1.4.0 |
| </option> |
| <option value="/v1_3_0/os/introduction" selected="selected" > |
| Version: 1.3.0 |
| </option> |
| <option value="/v1_2_0/os/introduction" > |
| Version: 1.2.0 |
| </option> |
| <option value="/v1_1_0/os/introduction" > |
| Version: 1.1.0 |
| </option> |
| <option value="/v1_0_0/os/introduction" > |
| Version: 1.0.0 |
| </option> |
| <option value="/v0_9_0/os/introduction" > |
| Version: 0.9.0 |
| </option> |
| </select></li> |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../../introduction/">Mynewt Documentation</a> |
| |
| |
| <ul> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../../get_started/get_started/">Basic Setup</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../../../get_started/vocabulary/">Concepts</a> |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../tutorials/">Tutorials</a> |
| |
| |
| <ul> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../blinky/">Project Blinky</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../repo/add_repos/">Work with repositories</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../project-slinky/">Project Slinky for Remote Comms</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../ble_bare_bones/ |
| ">Bluetooth Low Energy</a> |
| |
| |
| <ul> |
| |
| |
| |
| <li > |
| <a href="../../ble_bare_bones/">BLE Bare Bones Application</a> |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../../ibeacon/">BLE iBeacon</a> |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../../eddystone/">BLE Eddystone</a> |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../bleprph-intro/">BLE Peripheral Project</a> |
| |
| |
| <ul> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../bleprph-svc-reg/">Service Registration</a> |
| </li> |
| |
| |
| |
| |
| |
| <li class="active"> |
| <a href="./">Characteristic Access</a> |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../bleprph-adv/">Advertising</a> |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../bleprph-gap-event/">GAP Event Callbacks</a> |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../bleprph-app/">BLE Peripheral App</a> |
| </li> |
| |
| |
| |
| </ul> |
| |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../../blehci_project/">BLE HCI interface</a> |
| </li> |
| |
| |
| |
| </ul> |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../lora/lorawanapp/ |
| ">LoRa</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../event_queue/ |
| ">OS Fundamentals</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../add_newtmgr/ |
| ">Remote Device Management</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| |
| |
| ../../sensors/sensors/ |
| |
| ">Sensors</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../segger_rtt/ |
| ">Tooling</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../codesize/ |
| ">Other</a> |
| |
| |
| </li> |
| |
| |
| |
| </ul> |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../../os_user_guide/">OS User Guide</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../../../network/ble/ble_intro/ |
| ">BLE User Guide</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../../../newt/newt_intro/">Newt Tool Guide</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li ><a href="../../../../newtmgr/overview/">Newt Manager Guide</a> |
| |
| |
| </li> |
| |
| |
| |
| |
| |
| <li > |
| <a href="../../../../known_issues/">Known Issues</a> |
| </li> |
| |
| |
| |
| </ul> |
| |
| </li> |
| |
| |
| |
| |
| |
| |
| |
| <li><a href=" |
| ../../../../newt/install/prev_releases/ |
| ">Appendix</a> |
| |
| |
| </li> |
| |
| |
| |
| </ul> |
| </div></div> |
| |
| <div class="col-md-9" role="main"> |
| <div class="doc-header"> |
| <div role="navigation" aria-label="breadcrumbs navigation"> |
| <ul class="wy-breadcrumbs"> |
| <li><a href="/documentation/">Docs</a></li> |
| |
| |
| |
| <li>» <a href="os/tutorials/bleprph/bleprph-intro/">BLE Peripheral Project</a></li> |
| |
| |
| |
| <li>» <a href="os/tutorials/ble_bare_bones/">Bluetooth Low Energy</a></li> |
| |
| |
| |
| <li>» <a href="os/tutorials/tutorials/">Tutorials</a></li> |
| |
| |
| |
| <li>» <a href="os/introduction/">Mynewt Documentation</a></li> |
| |
| |
| |
| <li>» Characteristic Access</li> |
| |
| |
| |
| <li class="wy-breadcrumbs-aside"> |
| |
| <a href="https://github.com/apache/mynewt-site/blob/master/docs/os/tutorials/bleprph/bleprph-chr-access.md" |
| class="icon icon-github"> Edit on GitHub</a> |
| |
| </li> |
| |
| </ul> |
| </div> |
| </div> |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| <div class="alert alert-warning"> |
| <p> |
| Version 1.3.0 is not the most recent version of the Apache Mynewt |
| documentation. Click <a href="/latest">here</a> to read the latest |
| version. |
| </p> |
| </div> |
| |
| |
| |
| <h2 id="ble-peripheral-project">BLE Peripheral Project</h2> |
| <h3 id="characteristic-access">Characteristic Access</h3> |
| <p><br></p> |
| <h4 id="review">Review</h4> |
| <p>A characteristic's access callback implements its behavior. Recall that |
| services and characteristics are registered with NimBLE via attribute tables. |
| Each characteristic definition in an attribute table contains an <em>access_cb</em> |
| field. The <em>access_cb</em> field is an application callback that gets executed |
| whenever a peer device attempts to read or write the characteristic.</p> |
| <p>Earlier in this tutorial, we looked at how <em>bleprph</em> implements the GAP |
| service. Let's take another look at how <em>bleprph</em> specifies the first few |
| characteristics in this service.</p> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">static</span> <span style="color: #A90D91">const</span> <span style="color: #A90D91">struct</span> <span style="color: #3F6E75">ble_gatt_svc_def</span> <span style="color: #000000">gatt_svr_svcs</span>[] <span style="color: #000000">=</span> { |
| { |
| <span style="color: #177500">/*** Service: GAP. */</span> |
| .<span style="color: #000000">type</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_GATT_SVC_TYPE_PRIMARY</span>, |
| .<span style="color: #000000">uuid128</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_UUID16</span>(<span style="color: #000000">BLE_GAP_SVC_UUID16</span>), |
| .<span style="color: #000000">characteristics</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">ble_gatt_chr_def</span>[]) { { |
| <span style="color: #177500">/*** Characteristic: Device Name. */</span> |
| .<span style="color: #000000">uuid128</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_UUID16</span>(<span style="color: #000000">BLE_GAP_CHR_UUID16_DEVICE_NAME</span>), |
| .<span style="color: #000000">access_cb</span> <span style="color: #000000">=</span> <span style="color: #000000">gatt_svr_chr_access_gap</span>, |
| .<span style="color: #000000">flags</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_GATT_CHR_F_READ</span>, |
| }, { |
| <span style="color: #177500">/*** Characteristic: Appearance. */</span> |
| .<span style="color: #000000">uuid128</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_UUID16</span>(<span style="color: #000000">BLE_GAP_CHR_UUID16_APPEARANCE</span>), |
| .<span style="color: #000000">access_cb</span> <span style="color: #000000">=</span> <span style="color: #000000">gatt_svr_chr_access_gap</span>, |
| .<span style="color: #000000">flags</span> <span style="color: #000000">=</span> <span style="color: #000000">BLE_GATT_CHR_F_READ</span>, |
| }, { |
| <span style="color: #177500">// [...]</span> |
| </code></pre></div> |
| |
| <p>As you can see, <em>bleprph</em> uses the same <em>access_cb</em> function for all the GAP |
| service characteristics, but the developer could have implemented separate |
| functions for each characteristic if they preferred. Here is the <em>access_cb</em> |
| function that the GAP service characteristics use:</p> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">static</span> <span style="color: #A90D91">int</span> |
| <span style="color: #000000">gatt_svr_chr_access_gap</span>(<span style="color: #A90D91">uint16_t</span> <span style="color: #000000">conn_handle</span>, <span style="color: #A90D91">uint16_t</span> <span style="color: #000000">attr_handle</span>, <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">op</span>, |
| <span style="color: #A90D91">union</span> <span style="color: #3F6E75">ble_gatt_access_ctxt</span> <span style="color: #000000">*ctxt</span>, <span style="color: #A90D91">void</span> <span style="color: #000000">*arg</span>) |
| { |
| <span style="color: #A90D91">uint16_t</span> <span style="color: #000000">uuid16</span>; |
| |
| <span style="color: #000000">uuid16</span> <span style="color: #000000">=</span> <span style="color: #000000">ble_uuid_128_to_16</span>(<span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">chr->uuid128</span>); |
| <span style="color: #000000">assert</span>(<span style="color: #000000">uuid16</span> <span style="color: #000000">!=</span> <span style="color: #1C01CE">0</span>); |
| |
| <span style="color: #A90D91">switch</span> (<span style="color: #000000">uuid16</span>) { |
| <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_DEVICE_NAME</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_READ_CHR</span>); |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">void</span> <span style="color: #000000">*</span>)<span style="color: #000000">bleprph_device_name</span>; |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">=</span> <span style="color: #000000">strlen</span>(<span style="color: #000000">bleprph_device_name</span>); |
| <span style="color: #A90D91">break</span>; |
| |
| <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_APPEARANCE</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_READ_CHR</span>); |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">void</span> <span style="color: #000000">*</span>)<span style="color: #000000">&bleprph_appearance</span>; |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">=</span> <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_appearance</span>; |
| <span style="color: #A90D91">break</span>; |
| |
| <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_PERIPH_PRIV_FLAG</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_READ_CHR</span>); |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">void</span> <span style="color: #000000">*</span>)<span style="color: #000000">&bleprph_privacy_flag</span>; |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">=</span> <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_privacy_flag</span>; |
| <span style="color: #A90D91">break</span>; |
| |
| <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_RECONNECT_ADDR</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_WRITE_CHR</span>); |
| <span style="color: #A90D91">if</span> (<span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">!=</span> <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_reconnect_addr</span>) { |
| <span style="color: #A90D91">return</span> <span style="color: #000000">BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN</span>; |
| } |
| <span style="color: #000000">memcpy</span>(<span style="color: #000000">bleprph_reconnect_addr</span>, <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span>, |
| <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_reconnect_addr</span>); |
| <span style="color: #A90D91">break</span>; |
| |
| <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_PERIPH_PREF_CONN_PARAMS</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_READ_CHR</span>); |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">void</span> <span style="color: #000000">*</span>)<span style="color: #000000">&bleprph_pref_conn_params</span>; |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">=</span> <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_pref_conn_params</span>; |
| <span style="color: #A90D91">break</span>; |
| |
| <span style="color: #A90D91">default</span><span style="color: #000000">:</span> |
| <span style="color: #000000">assert</span>(<span style="color: #1C01CE">0</span>); |
| <span style="color: #A90D91">break</span>; |
| } |
| |
| <span style="color: #A90D91">return</span> <span style="color: #1C01CE">0</span>; |
| } |
| </code></pre></div> |
| |
| <p>After you've taken a moment to examine the structure of this function, let's explore some details.</p> |
| <p><br></p> |
| <h4 id="function-signature">Function signature</h4> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">static</span> <span style="color: #A90D91">int</span> |
| <span style="color: #000000">gatt_svr_chr_access_gap</span>(<span style="color: #A90D91">uint16_t</span> <span style="color: #000000">conn_handle</span>, <span style="color: #A90D91">uint16_t</span> <span style="color: #000000">attr_handle</span>, <span style="color: #A90D91">uint8_t</span> <span style="color: #000000">op</span>, |
| <span style="color: #A90D91">union</span> <span style="color: #3F6E75">ble_gatt_access_ctxt</span> <span style="color: #000000">*ctxt</span>, <span style="color: #A90D91">void</span> <span style="color: #000000">*arg</span>) |
| </code></pre></div> |
| |
| <p>A characteristic access function always takes this same set of parameters and |
| always returns an int. The parameters to this function type are documented |
| below.</p> |
| <p><br></p> |
| <table> |
| <thead> |
| <tr> |
| <th><strong>Parameter</strong></th> |
| <th><strong>Purpose</strong></th> |
| <th><strong>Notes</strong></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>conn_handle</td> |
| <td>Indicates which connection the characteristic access was sent over.</td> |
| <td>Use this value to determine which peer is accessing the characteristic.</td> |
| </tr> |
| <tr> |
| <td>attr_handle</td> |
| <td>The low-level ATT handle of the characteristic value attribute.</td> |
| <td>Can be used to determine which characteristic is being accessed if you don't want to perform a UUID lookup.</td> |
| </tr> |
| <tr> |
| <td>op</td> |
| <td>Indicates whether this is a read or write operation</td> |
| <td>Valid values are:<br><em>BLE_GATT_ACCESS_OP_READ_CHR</em><br><em>BLE_GATT_ACCESS_OP_WRITE_CHR</em></td> |
| </tr> |
| <tr> |
| <td>ctxt</td> |
| <td>Contains the characteristic value pointer that the application needs to access.</td> |
| <td>For characteristic accesses, use the <em>ctxt->chr_access</em> member; for descriptor accesses, use the <em>ctxt->dsc_access</em> member.</td> |
| </tr> |
| </tbody> |
| </table> |
| <p>The return value of the access function tells the NimBLE stack how to respond |
| to the peer performing the operation. A value of 0 indicates success. For |
| failures, the function returns the specific ATT error code that the NimBLE |
| stack should respond with. The ATT error codes are defined in |
| <a href="https://github.com/apache/incubator-mynewt-core/blob/master/net/nimble/host/include/host/ble_att.h">net/nimble/host/include/host/ble_att.h</a>.</p> |
| <p><br></p> |
| <h4 id="determine-characteristic-being-accessed">Determine characteristic being accessed</h4> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code>{ |
| <span style="color: #A90D91">uint16_t</span> <span style="color: #000000">uuid16</span>; |
| |
| <span style="color: #000000">uuid16</span> <span style="color: #000000">=</span> <span style="color: #000000">ble_uuid_128_to_16</span>(<span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">chr->uuid128</span>); |
| <span style="color: #000000">assert</span>(<span style="color: #000000">uuid16</span> <span style="color: #000000">!=</span> <span style="color: #1C01CE">0</span>); |
| |
| <span style="color: #A90D91">switch</span> (<span style="color: #000000">uuid16</span>) { |
| <span style="color: #177500">// [...]</span> |
| </code></pre></div> |
| |
| <p>This function uses the UUID to determine which characteristic is being |
| accessed. There are two alternative methods <em>bleprph</em> could have used to |
| accomplish this task:</p> |
| <ul> |
| <li>Map characteristics to ATT handles during service registration; use the <em>attr_handle</em> parameter as a key into this table during characteristic access.</li> |
| <li>Implement a dedicated function for each characteristic; each function inherently knows which characteristic it corresponds to.</li> |
| </ul> |
| <p>All the GAP service characteristics have 16-bit UUIDs, so this function uses |
| the <em>ble_uuid_128_to_16()</em> function to convert the 128-bit UUID to its |
| corresponding 16-bit UUID. This conversion function returns the corresponding |
| 16-bit UUID on success, or 0 on failure. Success is asserted here to ensure |
| the NimBLE stack is doing its job properly; the stack should only call this |
| function for accesses to characteristics that it is registered with, and all |
| GAP service characteristics have valid 16-bit UUIDs.</p> |
| <p><br></p> |
| <h4 id="read-access">Read access</h4> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code> <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_DEVICE_NAME</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_READ_CHR</span>); |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span> <span style="color: #000000">=</span> (<span style="color: #A90D91">void</span> <span style="color: #000000">*</span>)<span style="color: #000000">bleprph_device_name</span>; |
| <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">=</span> <span style="color: #000000">strlen</span>(<span style="color: #000000">bleprph_device_name</span>); |
| <span style="color: #A90D91">break</span>; |
| </code></pre></div> |
| |
| <p>This code excerpt handles read accesses to the device name characteristic. The |
| <em>assert()</em> here is another case of making sure the NimBLE stack is doing its |
| job; this characteristic was registered as read-only, so the stack should have |
| prevented write accesses.</p> |
| <p>To fulfill a characteristic read request, the application needs to assign the |
| <em>ctxt->chr_access.data</em> field to point to the attribute data to respond with, |
| and fill the <em>ctxt->chr_access.len</em> field with the length of the attribute data. |
| <em>bleprph</em> stores the device name in read-only memory as follows:</p> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">const</span> <span style="color: #A90D91">char</span> <span style="color: #000000">*bleprph_device_name</span> <span style="color: #000000">=</span> <span style="color: #C41A16">"nimble-bleprph"</span>; |
| </code></pre></div> |
| |
| <p>The cast to pointer-to-void is a necessary annoyance to remove the <em>const</em> |
| qualifier from the device name variable. You will need to "cast away const" |
| whenever you respond to read requests with read-only data.</p> |
| <p>It is not shown in the above snippet, but this function ultimately returns 0. |
| By returning 0, <em>bleprph</em> indicates that the characteristic data in |
| <em>ctxt->chr_access</em> is valid and that NimBLE should include it in its response |
| to the peer.</p> |
| <p><br></p> |
| <p><strong>A word of warning:</strong> The attribute data that <em>ctxt->chr_access.data</em> points to |
| must remain valid after the access function returns, as the NimBLE stack needs |
| to use it to form a GATT read response. In other words, you must not |
| allocate the characteristic value data on the stack of the access function. |
| Two characteristic accesses never occur at the same time, so it is OK to use |
| the same memory for repeated accesses.</p> |
| <p><br></p> |
| <h4 id="write-access">Write access</h4> |
| <p><br></p> |
| <div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code> <span style="color: #A90D91">case</span> <span style="color: #000000">BLE_GAP_CHR_UUID16_RECONNECT_ADDR</span>: |
| <span style="color: #000000">assert</span>(<span style="color: #000000">op</span> <span style="color: #000000">==</span> <span style="color: #000000">BLE_GATT_ACCESS_OP_WRITE_CHR</span>); |
| <span style="color: #A90D91">if</span> (<span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">len</span> <span style="color: #000000">!=</span> <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_reconnect_addr</span>) { |
| <span style="color: #A90D91">return</span> <span style="color: #000000">BLE_ATT_ERR_INVALID_ATTR_VALUE_LEN</span>; |
| } |
| <span style="color: #000000">memcpy</span>(<span style="color: #000000">bleprph_reconnect_addr</span>, <span style="color: #000000">ctxt->chr_access</span>.<span style="color: #000000">data</span>, |
| <span style="color: #A90D91">sizeof</span> <span style="color: #000000">bleprph_reconnect_addr</span>); |
| <span style="color: #A90D91">break</span>; |
| </code></pre></div> |
| |
| <p>This code excerpt handles writes to the reconnect address characteristic. This |
| characteristic was registered as write-only, so the <em>assert()</em> here is just a |
| safety precaution to ensure the NimBLE stack is doing its job.</p> |
| <p>For writes, the roles of the <em>ctxt->chr_access.data</em> and <em>ctxt->chr_access.len</em> |
| fields are the reverse of the read case. The NimBLE stack uses these fields to |
| indicate the data written by the peer.</p> |
| <p>Many characteristics have strict length requirements for write operations. |
| This characteristic has such a restriction; if the written data is not a 48-bit |
| BR address, the application tells NimBLE to respond with an invalid attribute |
| value length error.</p> |
| <p>For writes, the <em>ctxt->chr_access.data</em> pointer is only valid for the duration |
| of the access function. If the application needs to save the written data, it |
| should store it elsewhere before the function returns. In this case, <em>bleprph</em> |
| stores the specified address in a global variable called |
| <em>bleprph_reconnect_addr</em>.</p> |
| |
| <div class="row"> |
| |
| |
| |
| |
| <ul class="nav nav-pills" style="margin-bottom: 10px"> |
| <li> |
| |
| </li> |
| <li class="pull-right"> |
| |
| </li> |
| </ul> |
| </div> |
| <footer class="row"> |
| <div class="col-xs-12"> |
| |
| <p class="copyright">Apache Mynewt is available under Apache License, version 2.0.</p> |
| |
| </div> |
| <div class="col-xs-12"> |
| <div class="logos"> |
| <a href="https://www.apache.org/"> |
| <img src="/img/asf_logo_wide_small.png" alt="Apache" title="Apache"> |
| </a> |
| <p> |
| Copyright © 2015-2021 The Apache Software Foundation.<br> |
| <small class="footnote"> |
| Apache Mynewt, Mynewt, Apache, the Apache feather logo, and the Apache Mynewt |
| project logo are either registered trademarks or trademarks of the Apache |
| Software Foundation in the United States and other countries. |
| </small> |
| </p> |
| <a href=""> |
| <img src="https://www.countit.com/images/add_to_slack.png" alt="Slack Icon" title="Join our Slack Community" /> |
| </a> |
| </div> |
| </div> |
| <a href="https://www.apache.org/licenses/"> |
| <button class="button-footer-asf"> |
| License |
| </button> |
| </a> |
| <a href="https://www.apache.org/foundation/sponsorship.html"> |
| <button class="button-footer-asf"> |
| Sponsorship |
| </button> |
| </a> |
| <a href="https://www.apache.org/foundation/thanks.html"> |
| <button class="button-footer-asf"> |
| Thanks |
| </button> |
| </a> |
| <a href="https://www.apache.org/security/"> |
| <button class="button-footer-asf"> |
| Security |
| </button> |
| </a> |
| <a href="https://apache.org/events/current-event"> |
| <button class="button-footer-asf"> |
| ASF Events |
| </button> |
| </a> |
| </footer> |
| </div> |
| </div> |
| |
| |
| </div> |
| |
| <script src="../../../../js/jquery-1.10.2.min.js"></script> |
| <script src="../../../../js/bootstrap-3.0.3.min.js"></script> |
| <script src="../../../../js/highlight.pack.js"></script> |
| <script src="../../../../js/base.js"></script> |
| <script src="../../../../js/custom.js"></script> |
| <script src="search/main.js"></script> |
| |
| </body> |
| </html> |