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<title>3. DATA STRUCTS — Byte Rider 06-2025 documentation</title>
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<section id="data-structs">
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<h1><span class="section-number">3. </span>DATA STRUCTS<a class="headerlink" href="#data-structs" title="Link to this heading">¶</a></h1>
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<p>The struct serves as the data payload for sending control signals from the transmitting device to the receiver using ESP-NOW.
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In addition, it may contain additional data such as telemetry, battery status, etc. The <em>sensors_data_t</em> struct encapsulates all control commands and sensor states
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relevant to the vehicle’s operation. It’s intended to be sent from a transmitting device (like a remote control) to a receiver
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(such as a microcontroller on board of the vehicle).</p>
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<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p">{</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">x_axis</span><span class="p">;</span><span class="w"> </span><span class="c1">// Joystick x-position</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">y_axis</span><span class="p">;</span><span class="w"> </span><span class="c1">// Joystick y-position</span>
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<span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">nav_bttn</span><span class="p">;</span><span class="w"> </span><span class="c1">// Joystick push button</span>
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<span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">led</span><span class="p">;</span><span class="w"> </span><span class="c1">// LED ON/OFF state</span>
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<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">motor1_rpm_pwm</span><span class="p">;</span><span class="w"> </span><span class="c1">// PWMs for 4 DC motors</span>
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<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">motor2_rpm_pwm</span><span class="p">;</span>
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<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">motor3_rpm_pwm</span><span class="p">;</span>
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<span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">motor4_rpm_pwm</span><span class="p">;</span>
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<span class="p">}</span><span class="w"> </span><span class="n">__attribute__</span><span class="p">((</span><span class="n">packed</span><span class="p">))</span><span class="w"> </span><span class="n">sensors_data_t</span><span class="p">;</span>
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</pre></div>
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</div>
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<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">motors_rpm</span><span class="w"> </span><span class="p">{</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor1_rpm_pwm</span><span class="p">;</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor2_rpm_pwm</span><span class="p">;</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor3_rpm_pwm</span><span class="p">;</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">motor4_rpm_pwm</span><span class="p">;</span>
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<span class="p">};</span>
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</pre></div>
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</div>
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<p>When used with communication protocols like ESP-NOW, this struct is <strong>encoded</strong> into a byte stream, then
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<strong>transmitted</strong> at regular intervals or in response to user input, and finally
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<strong>decoded</strong> on the receiving end to control hardware.</p>
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<div class="admonition-what-is-struct admonition">
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<p class="admonition-title">What is struct?</p>
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<p>In C programming, a struct (short for structure) is a user-defined data type that lets you group multiple variables of different types together under a
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single name. It’s like a container that holds related information — perfect for organizing data that logically belongs together. Structs are especially
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powerful in systems programming, embedded projects, and when dealing with raw binary data — like parsing sensor input or transmitting control packets over
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ESP-NOW.</p>
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</div>
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<section id="data-payload">
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<h2><span class="section-number">3.1. </span>Data Payload<a class="headerlink" href="#data-payload" title="Link to this heading">¶</a></h2>
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<p><em>x_axis</em> and <em>y_axis</em> fields capture analog input from a joystick, determining direction and speed.
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<em>nav_bttn</em> represents a joystick push-button.</p>
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<p><em>led</em> allows the transmitter to toggle an onboard LED and is used for status indication (e.g. pairing, battery warning, etc).</p>
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<p><em>motor1_rpm_pwm</em> to <em>motor4_rpm_pwm</em> provide individual PWM signals to four DC motors.
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This enables fine-grained speed control, supports differential drive configurations, and even allows for maneuvering in multi-directional platforms like omni-wheel robots.</p>
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<section id="why-use-attribute-packed">
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<h3><span class="section-number">3.1.1. </span>Why use __attribute((packed))?<a class="headerlink" href="#why-use-attribute-packed" title="Link to this heading">¶</a></h3>
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<p>ESP-NOW uses fixed-size data packets (up to 250 bytes). The <em>__attribute__((packed))</em> removes compiler-added padding for precise byte alignment.</p>
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<p>As <em>packed</em> attribute tells the compiler not to add any padding between fields in memory, this makes the struct:</p>
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<blockquote>
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<div><ul class="simple">
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<li><p>Compact</p></li>
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<li><p>Predictable for serialization over protocols like UART or ESP-NOW</p></li>
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<li><p>Ideal for low-latency transmission in embedded systems</p></li>
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</ul>
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</div></blockquote>
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<p>This ensures the receiver interprets the exact byte layout you expect, minimizing bandwidth and maximizing compatibility across platforms.</p>
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</section>
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<script>document.getElementById('searchbox').style.display = "block"</script><h3>Navigation</h3>
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<ul class="current">
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<li class="toctree-l1"><a class="reference internal" href="intro.html">1. OVERVIEW</a></li>
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<li class="toctree-l1"><a class="reference internal" href="overview.html">2. HOW DOES IT WORK?</a></li>
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<li class="toctree-l1 current"><a class="current reference internal" href="#">3. DATA STRUCTS</a><ul>
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<li class="toctree-l2"><a class="reference internal" href="#data-payload">3.1. Data Payload</a><ul>
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<li class="toctree-l3"><a class="reference internal" href="#why-use-attribute-packed">3.1.1. Why use __attribute((packed))?</a></li>
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<li class="toctree-l1"><a class="reference internal" href="transmitter.html">4. TRANSMITTER</a></li>
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<li class="toctree-l1"><a class="reference internal" href="receiver.html">5. RECEIVER</a></li>
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<li class="toctree-l1"><a class="reference internal" href="progress.html">6. WORK-IN-PROGRESS WALK THROUGH</a></li>
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<li class="toctree-l1"><a class="reference internal" href="references.html">7. REFERENCES</a></li>
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<li><a href="index.html">Documentation overview</a><ul>
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<li>Previous: <a href="overview.html" title="previous chapter"><span class="section-number">2. </span>HOW DOES IT WORK?</a></li>
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