Module example ( input C, output reg Q ) reg counter always posedge C ) begin counter <= counter + 1 'b1 end always posedge C ) begin Q <= counter ^ counter | counter << 2 end endmodule Here is an example of a counter module with a registered output: Inside an existing programming language, such as how Migen is embedded in Python,Ĭlash is embedded in Haskell, or Chisel and SpinalHDL are embedded in Scala. Is to achieve hardware description by embedding a Domain Specific Language (DSL) Two most common languages are Verilog and VHDL. That allow us to describe the expected behaviour and/or structure. Hard and very challenging so people have come up with abstract Turning code into gates ¶Ĭonfiguring all the LUTs, carry logic and other hard blocks manually is At the same time,Ĭustom behaviour can only be described through LUTs, because all hard blocksĪre programmable within the pre-fixed functionality only. Of any of those hard blocks can be replicated using PLBs only. Those so-called hard blocks allow betterĪrea and power usage than LUT-based components. These resources allow combining multiple LUTs forĭescribing larger logical functions and for providing sequential behaviour.įurthermore, additional purpose-specific blocks are included in the devices:īlock RAMs (BRAMs), Digital Signal Processing (DSP) blocks, high-performance serial So-called Programmable Logic Blocks (PLBs) or Configurable Logic Blocks (CLBs) ĭepending on the vendor. Typically, LUTs are grouped with flip-flop registers (DFF) and some carry logic, in Modern FPGA devices are no longer composed of arrays of gates (i.e. Programmable Logic Block (PLB), Block Diagram. It is from this simple primitive that we create the building logic blocks of Conversely, to createĪ NAND gate, we would define O to be 1 for everything except the last column. O to be 0 for everything except the last column. To do this, we turn toįor example, to create a LUT that acted as an AND gate, we would define To program Fomu, we must define whatĮach possible input 4-bit pattern will create on the output. Has four 1-bit inputs and one 1-bit output. The basic building block of Fomu is the SB_LUT4. The ICE40 LUT4 is a basic 4-input 1-output function table. Xilinx parts tend to have 5-input orĦ-input LUTs which generally means they can do more logic in fewer LUTs.Ĭomparing LUT count between FPGAs is a bit like comparing clock speedīetween different CPUs not entirely accurate, but certainly a helpful The ICE family ofįPGAs from Lattice have 4-input LUTs. Which had about 9000 LUTs, and NeTV2 uses a XC7A35TįPGA LUTs are almost always n-inputs to 1-output. These lookup tables are so important to the design and usage of anįPGA that they usually form part of the name of the part. Conversely, FPGAsĬan change their internal connections by simply loading new configurations.įundamentally, configurations program lookup tables (LUTs), which form the basicīuilding blocks of logic. In a fixed order, thus providing a fixed functionality. Most chips you will encounter, have transistor gates arranged Are integrated circuits containing arrays of gates which are programmable
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