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| <section id="place-route"> |
| <h1 id="flows-pnr--page-root">Place & Route<a class="headerlink" href="#flows-pnr--page-root" title="Link to this heading">¶</a></h1> |
| <p>The Synthesis process results in an output containing logical elements |
| available on the desired FPGA chip with the specified connections between them. |
| However, it does not specify the physical layout of those elements in the |
| final design. The goal of the Place and Route (PnR) process is to take the |
| synthesized design and implement it into the target FPGA device. The PnR tool |
| needs to have information about the physical composition of the device, routing |
| paths between the different logical blocks and signal propagation timings. |
| The working flow of different PnR tools may vary, however, the process presented |
| below represents the typical one, adopted by most of these tools. Usually, it |
| consists of four steps - packing, placing, routing and analysis.</p> |
| <section id="packing"> |
| <h2 id="packing">Packing<a class="headerlink" href="#packing" title="Link to this heading">¶</a></h2> |
| <p>In the first step, the tool collects and analyzes the primitives present |
| in the synthesized design (e.g. Flip-Flops, Muxes, Carry-chains, etc), and |
| organizes them in clusters, each one belonging to a physical tile of the device. |
| The PnR tool makes the best possible decision, based on the FPGA routing |
| resources and timings between different points in the chip.</p> |
| </section> |
| <section id="placing"> |
| <h2 id="placing">Placing<a class="headerlink" href="#placing" title="Link to this heading">¶</a></h2> |
| <p>After having clustered all the various primitives into the physical tiles of the |
| device, the tool begins the placement process. This step consists in assigning a |
| physical location to every cluster generated in the packing stage. The choice of |
| the locations is based on the chosen algorithm and on the user’s parameters, but |
| generally, the final goal is to find the best placement that allows the routing |
| step to find more optimal solutions.</p> |
| </section> |
| <section id="routing"> |
| <h2 id="routing">Routing<a class="headerlink" href="#routing" title="Link to this heading">¶</a></h2> |
| <p>Routing is one of the most demanding tasks of the whole process. |
| All possible connections between the placed blocks and the information on |
| the signals propagation timings, form a complex graph. |
| The tool tries to find the optimal path connecting all the placed |
| clusters using the information provided in the routing graph. Once all the nets |
| have been routed, an output file containing the implemented design is produced.</p> |
| </section> |
| <section id="analysis"> |
| <h2 id="analysis">Analysis<a class="headerlink" href="#analysis" title="Link to this heading">¶</a></h2> |
| <p>This last step usually checks the whole design in terms of timings and power |
| consumption.</p> |
| </section> |
| </section> |
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