Risc-V Board Multiplier Use and ISIM Simulation
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Risc-V Board Tutorial : Multiplier Use and ISIM Simulation- FII-PRX100 FPGA Board Experiment 7

Experiment 7 Multiplier Use and ISIM Simulation

1.Experiment Objective

    1. Learn to use multiplier
    2. Use ISIM to simulate design output

2.Experiment Design

    1. Build new project mult_sim
          1. Select device XC7A100TFGG676-2
    2. Design requirement
      1. 8×8 multiplier, the first input value is an 8-bit switch, and the second input value is the output of an 8-bit counter.
      2. Observe the result on Modelsim
      3. Observe the result on 6 segment decoders
    3. Design procedure
      1. Create new file mult_sim.v
      2.  Add PLL,set the input clock to be 50 MHz, and the output clock to be 100 MHz
      3. Add LPM_MULT IP

IP Catalog -> input Mult in the search box. Invoke the multipliers. See Fig 7. 1.

Fig 7. 1 Build IP core for multiplier

      1. Choose input data type to be unsigned. See Fig 7. 2.

Fig 7. 2 Set the input data type and data width

      1. Choose Pipelining and Control Signals. See Fig 7. 3. Add a delay of 1 stage. The default optimum stage is 3 stages.

Fig 7. 3 Pipelining setting

    1. Choose default for other settings
    2. Instantiate in the top-level entity

3.The Top-level Entity Is as Follows:

module mult_sim


input rst,

input inclk,

input [7:0] sw,

output [6:0] seven_seg,

output [3:0] scan


wire [15:0] mult_res;

wire sys_clk;

wire sys_rst;

reg [7:0] count;

always@(posedge sys_clk)







.clock (sys_clk),

.dataa (sw),

.datab (count),

.result (mult_res)


pll_sys_rst pll_sys_rst_inst


.inclk (inclk),

.sys_clk (sys_clk),

.sys_rst (sys_rst)



4.ISIM Simulation Library Compilation and Call

Under the Vivado platform, you can choose to use built-in simulation tool ISIM or third-party simulation tools for functional simulation of the project. Simulating with the Modelsim simulation tool requires a separate compilation of the simulation library. This routine uses the built-in ISIM tool emulation and briefly introduce Modelsim’s Xilinx simulation library file compilation for simulation using Modelsim.

  1. Build simulation project. Tools -> Compile Simulation Libraries. See Fig 7. 4 for the popup window.

Fig 7. 4 Compilation library address setting

Simulation testbench code is as follows:

module mult_sim_tb;

//Define simulation signals

reg rst_n;

reg [7:0] sw;

reg clk;

wire [7:0] seven_seg;

wire [3:0] scan;

wire [15:0] mult_res;

wire [7: 0] count ;

mult_sim mult_sim_inst













clk = 1;

sw = 0;

#5 rst_n=1;

#15 sw = 20;

#20 sw = 50;

#20 sw = 100;

#20 sw = 101;

#20 sw = 102;

#20 sw = 103;

#20 sw = 104;

#50 sw = 105;

$monitor(“%d * %d=%d”, count, sw, mult_res);

#1000000 $stop;



#10 clk=~clk;


  1. As shown in Fig 7. 5, after the simulation stimulus file is added, ISIM can be started in Simulation->Run Simulation –> Run Behavioral Simulation on the left side of the project management.

Fig 7. 5 Simulation library compiled

  1. Simulation result is shown in Fig 7. 6.

Fig 7. 6 Simulation result

  1. Compile ModelSim library

After installing ModelSim, compile the Xilinx simulation library file first. The specific process is as follows:

      1. Tools -> Compile Simulation Libraries. See Fig 7. 7 for the popup window.

Fig 7. 7 Compilation library address setting

      1. As shown in Fig 7. 8, the compilation is completed. Note that the process is very time consuming.

Fig 7. 8 Simulation library compiled

Approachable advanced information for ModelSim can be referred online. Here would not go into more details.

  1. More to practice
    1. Design an 8-bit trigger, simulate with Modelsim
    2. Learn to write testbenchs for simulation

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