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| <span class="target" id="mdio-bus"></span><section id="mdio-bus-driver"> |
| <h1>MDIO Bus Driver<a class="headerlink" href="#mdio-bus-driver" title="Permalink to this heading"></a></h1> |
| <p>The NuttX MDIO bus driver provides a standardized interface for communicating with Ethernet PHY (Physical Layer) transceivers. |
| It employs a classic upper-half/lower-half architecture to abstract hardware-specific logic from the generic MDIO protocol, |
| which is currently compliant with Clause 22 of the IEEE 802.3 standard. |
| The primary implementation of the upper-half can be found in <code class="docutils literal notranslate"><span class="pre">drivers/net/mdio.c</span></code>.</p> |
| <section id="driver-architecture"> |
| <h2>Driver Architecture<a class="headerlink" href="#driver-architecture" title="Permalink to this heading"></a></h2> |
| <p>The MDIO driver framework serves as an intermediary layer between a network device driver and the physical bus. |
| The intended operational model is <code class="docutils literal notranslate"><span class="pre">netdev</span> <span class="pre">-></span> <span class="pre">phydev</span> <span class="pre">-></span> <span class="pre">mdio</span></code>, where the network device communicates with a dedicated PHY driver, |
| which in turn uses the MDIO bus driver for low-level hardware access. |
| Direct interaction between the network device and the MDIO bus is discouraged.</p> |
| <section id="upper-half-implementation"> |
| <h3>Upper-Half Implementation<a class="headerlink" href="#upper-half-implementation" title="Permalink to this heading"></a></h3> |
| <p>The upper-half driver contains the core logic for the MDIO bus, including bus locking mechanisms to ensure safe transactions. |
| It exposes a generic API for managing the bus lifecycle and is capable of handling multiple, independent MDIO bus instances concurrently. |
| This abstracts implementation details from both the PHY driver and the underlying hardware-specific code.</p> |
| </section> |
| <section id="lower-half-implementation"> |
| <h3>Lower-Half Implementation<a class="headerlink" href="#lower-half-implementation" title="Permalink to this heading"></a></h3> |
| <p>A lower-half MDIO driver serves as a thin layer that maps the generic operations defined by the upper-half to hardware-specific register manipulations. |
| It is not intended to contain complex logic, but rather to provide a direct translation for bus operations.</p> |
| </section> |
| </section> |
| <section id="implementing-a-lower-half-driver"> |
| <h2>Implementing a Lower-Half Driver<a class="headerlink" href="#implementing-a-lower-half-driver" title="Permalink to this heading"></a></h2> |
| <p>Integrating MDIO support for new hardware requires the implementation of a lower-half driver. |
| The contract between the upper and lower halves is defined in <code class="docutils literal notranslate"><span class="pre">include/nuttx/net/mdio.h</span></code> and is centered around two key structures.</p> |
| <section id="key-data-structures"> |
| <h3>Key Data Structures<a class="headerlink" href="#key-data-structures" title="Permalink to this heading"></a></h3> |
| <ol class="arabic simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">mdio_ops_s</span></code>: A structure containing function pointers that the lower-half driver must implement to perform hardware-level operations. |
| * <code class="docutils literal notranslate"><span class="pre">read</span></code>: Performs a Clause 22 MDIO read operation. |
| * <code class="docutils literal notranslate"><span class="pre">write</span></code>: Performs a Clause 22 MDIO write operation. |
| * <code class="docutils literal notranslate"><span class="pre">reset</span></code>: An optional function to execute a hardware-specific PHY reset.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">mdio_lowerhalf_s</span></code>: The container for the lower-half instance, which holds a pointer to the <code class="docutils literal notranslate"><span class="pre">mdio_ops_s</span></code> vtable |
| and an optional private data pointer for the driver’s internal state.</p></li> |
| </ol> |
| </section> |
| <section id="registration-and-unregistration"> |
| <h3>Registration and Unregistration<a class="headerlink" href="#registration-and-unregistration" title="Permalink to this heading"></a></h3> |
| <p>The board-level initialization logic is responsible for instantiating the lower-half driver and registering it with the upper-half via the <code class="docutils literal notranslate"><span class="pre">mdio_register()</span></code> function. |
| Each call to this function with a distinct lower-half driver creates a new, unique bus handle, allowing the system to manage several MDIO buses concurrently.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">FAR</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">mdio_dev_s</span><span class="w"> </span><span class="o">*</span><span class="n">mdio_register</span><span class="p">(</span><span class="n">FAR</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">mdio_lowerhalf_s</span><span class="w"> </span><span class="o">*</span><span class="n">lower</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>This function accepts the lower-half instance and returns an opaque handle (<code class="docutils literal notranslate"><span class="pre">FAR</span> <span class="pre">struct</span> <span class="pre">mdio_dev_s</span> <span class="pre">*</span></code>), |
| which is subsequently used by the PHY driver to interact with the bus.</p> |
| <p>When a bus instance is no longer required, it should be deallocated by calling the <code class="docutils literal notranslate"><span class="pre">mdio_unregister()</span></code> function to ensure proper cleanup of resources.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="nf">mdio_unregister</span><span class="p">(</span><span class="n">FAR</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">mdio_dev_s</span><span class="w"> </span><span class="o">*</span><span class="n">dev</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>This function takes the handle returned by <code class="docutils literal notranslate"><span class="pre">mdio_register()</span></code> and releases the associated bus instance.</p> |
| <p>A (mostly) complete reference implementation for a lower-half driver is available in <code class="docutils literal notranslate"><span class="pre">arch/arm/src/stm32h7/stm32_mdio.c</span></code>.</p> |
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