Post-Synthesis Simulationĭuring the synthesis process, we can request that the tool generates a netlist in either VHDL or verilog. As the timing is dependent on the location of cells in the FPGA, results are more accurate following this process. We typically analyse the timing of a design in more detail following the place and route process. As a result of this, we can't guarantee that our device will operate as expected. When our design can't be run at the desired frequency then we can not be sure that there will will be no timing violations on the internal flip flops. We use this analysis to determine whether the FPGA can run our design at the required frequency. We can also analyse the timing of our FPGA after we have run the synthesus. Fpga how it works code#If this doesn't sufficiently reduce utilisation then we must select a new FPGA or make our original code more efficient. This reduction can be enough if our design is only slightly larger than our chosen FPGA. Examples of this could be changing FSM encoding or selecting a different synthesis algorithm. It is normally possible to reduce utilisation by changing the configuration of the synthesis tool. There are a number of options available to us when this occurs. High end chips can also include dedicated DSP core, clock management blocks such as PLLs as well as other peripheral interfaces such as ADCs or dedicated high speed interfaces.Īfter completing the synthesis process, we can generate a report which tells us how many cells are used in our design both in absolute terms and as a percentage of all available cells in the device.Īfter running the synthesis process it is not uncommon to find that our design is too big for our device. The individual cells within a device vary from chip to chip, as well as between vendors.Īlmost all modern chips will include RAM, some form of LUT and flip flops. This analysis details how many of each of the different types of FPGA cells our design uses. The first of these analyses is the logic utilisation of the design. However, this information is typically more reliable after the place and route process. We can also perform some analyses of our design as a part of the synthesis process. These details determine how much effort the synthesiser puts into optimising timing within the FPGA. This includes information such as the clock frequency, the number of clock domains and the timing of external interfaces. We use timing constraints to define details about the FPGA which can’t be specified in the source code. In addition to this, it is good practise to create a file which defines the timing constraints of the design. This script typically tells the tool which FPGA to target, the pinout of the design and which strategy to use when running the synthesis. We also need a script or project file which defines the configuration of the synthesis tool. The first of these is the source code for our design. The synthesis process requires at least two inputs. We normally only need the paid tools for large or high speed designs. Fpga how it works free#The paid tools are typically capable of delivering more optimised netlists than the free tools. The most well known of these tools are Synplify Pro from Synopsys and Leonardo Spectrum from Mentor Graphics. There are also paid tools which we can use for this pirpose. The most popular of these tools is yosys which is frequently used with Lattice FPGAs. In addition to this, there are also a number of open source synthesis tools which we can use. There are a number of different tools we can use to run the synthesis process.īoth of the major FPGA vendors ( Xilinx and Intel) offer free synthesis tools which are suitable for most projects. This can be any digital element in the FPGA such as flip-flops, RAM or look up tables (LUT). In this context, the macros are actually models of the internal FPGA cells. This has the effect of creating a flat hierarchical circuit diagram which implements the RTL design. This process transforms the functional RTL design into an array of gate level macros. The first stage in building the FPGA is known as synthesis. We discuss each of these steps in more detail in the rest of this post. We normally carry this out in three separate stages - synthesis, place and route and generation of the programming file. Once we have proven our design works, we then transfer the functional HDL code into an actual FPGA. Fpga how it works series#In the previous post in this series we talked about the process of creating an FPGA design. In this post we cover the three major steps involved in this process - synthesis, place and route and finally programming file generation. This process involves taking an existing HDL based design and creating a programming file for our target FPGA. In this post we talk about the FPGA implementation process.
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