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<title>lwIP: Zero-copy RX</title>
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   <div id="projectname">lwIP
   &#160;<span id="projectnumber">2.1.2</span>
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   <div id="projectbrief">Lightweight IP stack</div>
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<div class="title">Zero-copy RX </div>  </div>
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<div class="textblock"><p>The following code is an example for zero-copy RX ethernet driver: </p><div class="fragment"><div class="line"><span class="keyword">typedef</span> <span class="keyword">struct </span>my_custom_pbuf</div><div class="line">{</div><div class="line">   <span class="keyword">struct </span><a class="code" href="structpbuf__custom.html">pbuf_custom</a> p;</div><div class="line">   <span class="keywordtype">void</span>* dma_descriptor;</div><div class="line">} my_custom_pbuf_t;</div><div class="line"></div><div class="line"><a class="code" href="group__mempool.html#ga5b1fb3ce7942432d87cc948b1c5ed6cb">LWIP_MEMPOOL_DECLARE</a>(RX_POOL, 10, <span class="keyword">sizeof</span>(my_custom_pbuf_t), <span class="stringliteral">&quot;Zero-copy RX PBUF pool&quot;</span>);</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> my_pbuf_free_custom(<span class="keywordtype">void</span>* p)</div><div class="line">{</div><div class="line">  <a class="code" href="group__sys__prot.html#ga945395fa326214fc9736487242710a90">SYS_ARCH_DECL_PROTECT</a>(old_level);</div><div class="line"></div><div class="line">  my_custom_pbuf_t* my_puf = (my_custom_pbuf_t*)p;</div><div class="line"></div><div class="line">  <span class="comment">// invalidate data cache here - lwIP and/or application may have written into buffer!</span></div><div class="line">  <span class="comment">// (invalidate is faster than flushing, and noone needs the correct data in the buffer)</span></div><div class="line">  invalidate_cpu_cache(p-&gt;payload, p-&gt;tot_len);</div><div class="line"></div><div class="line">  <a class="code" href="group__sys__prot.html#ga3d0e48feafd378e9c26c64567ecd8bab">SYS_ARCH_PROTECT</a>(old_level);</div><div class="line">  free_rx_dma_descriptor(my_pbuf-&gt;dma_descriptor);</div><div class="line">  <a class="code" href="group__mempool.html#gaa43d114dd702fbd8f1db18474ea93a04">LWIP_MEMPOOL_FREE</a>(RX_POOL, my_pbuf);</div><div class="line">  <a class="code" href="group__sys__prot.html#ga2f48e97047945642ddeb27e65bf4ffe2">SYS_ARCH_UNPROTECT</a>(old_level);</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> eth_rx_irq()</div><div class="line">{</div><div class="line">  dma_descriptor*   dma_desc = get_RX_DMA_descriptor_from_ethernet();</div><div class="line">  my_custom_pbuf_t* my_pbuf  = (my_custom_pbuf_t*)<a class="code" href="group__mempool.html#ga5e2498f6c17746c1fe7153de5f7f275a">LWIP_MEMPOOL_ALLOC</a>(RX_POOL);</div><div class="line"></div><div class="line">  my_pbuf-&gt;p.custom_free_function = my_pbuf_free_custom;</div><div class="line">  my_pbuf-&gt;dma_descriptor         = dma_desc;</div><div class="line"></div><div class="line">  invalidate_cpu_cache(dma_desc-&gt;rx_data, dma_desc-&gt;rx_length);</div><div class="line">  </div><div class="line">  <span class="keyword">struct </span><a class="code" href="structpbuf.html">pbuf</a>* p = <a class="code" href="group__pbuf.html#ga90fa2bbf6ea4a263ee8f7b77c75683c2">pbuf_alloced_custom</a>(<a class="code" href="group__pbuf.html#ggaee1baa59bb2f85ba575b5a8619ac1ebfa21116654fbab6d5a4dfeb87a1bb8f0ba">PBUF_RAW</a>,</div><div class="line">     dma_desc-&gt;rx_length,</div><div class="line">     <a class="code" href="group__pbuf.html#ggab7e0e32fcc292c0d7107721766ed92fbac9b6ba960fdea6f2e8f35c8313b77e4e">PBUF_REF</a>,</div><div class="line">     &amp;my_pbuf-&gt;p,</div><div class="line">     dma_desc-&gt;rx_data,</div><div class="line">     dma_desc-&gt;max_buffer_size);</div><div class="line"></div><div class="line">  <span class="keywordflow">if</span>(<a class="code" href="structnetif.html">netif</a>-&gt;<a class="code" href="structnetif.html#a8fe4f1b7b0d710216287da9615164a5c">input</a>(p, <a class="code" href="structnetif.html">netif</a>) != <a class="code" href="group__infrastructure__errors.html#ggae2e66c7d13afc90ffecd6151680fbadcaa26c163b80b1f6786ca81dadc14b00fb">ERR_OK</a>) {</div><div class="line">    <a class="code" href="group__pbuf.html#gab0dd696fb4b6bc65e548944584f1738b">pbuf_free</a>(p);</div><div class="line">  }</div><div class="line">}</div></div><!-- fragment --> </div></div><!-- contents -->
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