Very simple I2C monitor for digital simulation in Verilog

//System Verilog I2C simulation monitor module 

module i2cMon;

wire SCL = testbench_top.dut.SCLK;

wire SDA = testbench_top.dut.SDA;

integer pattern_cnt;

integer bit_cnt;

reg [7:0] byte_rec;

initial begin

pattern_cnt = 0;

bit_cnt = 0;

end

always @(negedge SDA) begin

    #1;

    if(SCL === 1'b1) begin //START PKT

        bit_cnt =0;

        pattern_cnt = pattern_cnt +1;

        $display ("i2cMon: PKT %d",pattern_cnt );

    end //end START PKT

end

always @(posedge SCL) begin

if(bit_cnt <8) begin

        byte_rec[7-bit_cnt] = SDA;

        bit_cnt = bit_cnt+1;

end

else begin

         $display ("i2cMon: Byte = %h ,ACK = %b", byte_rec, SDA);

         bit_cnt = 0;

    end

end

endmodule

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This is a free online digital diagram drawing program. Free to use and no login required.

Use simple text symbols (case sensitive) to specify the drawing mode of the diagram in text boxes. 7 digital traces can be shown in each diagram. Simple rules are specified below and in the example tutorial.

Signal: Support Signal name, 0 ->logic low, 1 ->logic high, Z ->high Impedance

Bus: Support Bus Name, H ->value high, L ->value low, Z -> high Impedance, X ->unknown

Marker: Specified with symbol M

Notation: Marked in between two single quotes

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An Example of Verilog Sync RAM

// Verilog RTL Port SRAM
// Synch. RAM 32x256
// INTEL MICRO CORP
module DPRAM (
              input wire       mem_clk,   // RTL RAM clock
 input wire [7:0] wrAddr,
 input wire [31:0] dprIn,
 input wire dprWe,  // Write enable
 input wire [7:0] rdAddr,
 output reg [31:0] dprOut
                    );
reg [31:0] memArray [0:255];
always @ (posedge mem_clk) begin
if(dprWe) memArray[wrAddr] <= dprIn;
dprOut <= memArray[rdAddr];
end
endmodule

Note About Using Verilog Task and Functions

Tasks & Functions

• Both tasks and functions are defined locally in the module in which the tasks and functions will be invoked. 
• No initial or always statement may be defined within either tasks or functions.
• Tasks and functions are different — task may have 0 or more arguments of type input, output or inout ; function must have at least one input argument. 
• Tasks do not return value but pass values through output and inout arguments; functions always return a single value, but cannot have output or inout arguments. 
• Tasks may contain delay, event or timing control statements; functions may not. 
• Tasks can invoke other tasks and functions; functions can only invoke other functions, but not tasks.

module TestTop;
 reg [1:0] r1;
 reg [3:0] r2;
 reg r3;

 initial begin
 r1 = 2'b01;
 r2 = myFunc(r1); // Invoke function
 $display("r2 = %b", r2);

 myTask (r2, r3); // Invoke task
 $display("myTask return = %d",r3);

 end

 task myTask;
 input [3:0] i;
 output myTaskOut;
 begin
 #10;
 myTaskOut = (i == 4'b0101);
 end
 endtask

 function [3:0] myFunc;
 input [1:0] i;
 begin
 myFunc = {i,i}; // Return value
 end
 endfunction

endmodule

Advanced Usage of Verilog Date Types

a) Physical data type
• Net (wire, wand, wor, tri, triand, trior). Default value is z. Used mainly in structural modeling.
• Register (reg). Default value is x. Used in dataflow/RTL and behavioral modelings.
• Charge storage node (trireg). Default value is x. Used in gate-level and switchlevel modelings.

b) Abstract data type — used only in behavioral modeling and test fixture.
• Integer (integer) stores 32-bit signed quantity.
• Time (time) stores 64-bit unsigned quantity from system task $time.
• Real (real) stores floating-point quantity.
• Parameter (parameter) substitutes constant.
• Event (event) is only name reference — does not hold value.

Examples:
4'b1011 // 4-bit binary of value 1011
234 // 3-digit decimal of value 234
2'h5a // 2-digit (8-bit) hexadecimal of value 5A
3'o671 // 3-digit (9-bit) octal of value 671
4b'1x0z // 4-bit binary. 2nd MSB is unknown. LSB is Hi-Z.
3.14 // Floating point
1.28e5 // Scientific notation

How to use verilog "parameter"

Parameterized Instantiations
The values of parameters can be overridden during instantiation of leave as default.
Or "defparam" statement can be used for the same purpose.

module myGate ( a, b, c, d );
 parameter x = 0;
 input a, b;
 output c, d;
 parameter y = 0, z = 0;
 ...
endmodule
module top;
 reg A, B;
 wire C, D;
 myGate #(2, 4, 3) m1 (A, B, C, D);
// x = 2, y = 4, z = 3 in instance m1
                                                        
 myGate #(5, 3, 1) m2 (.b(B), .d(D), .c(C), .a(A));
// x = 5, y = 3, z = 1 in instance m2        
                                                                 
 defparam m3.x = 4, m3.y = 2, m3.z = 5;
 myGate m3 (A, B, C, D); // x = 4, y = 2, z = 5 in instance m3
 ...
endmodule

Verilog CASE statement example with State Machine

//An example of verilog case statement

module caseExample( input wire clock, input wire resetn, output reg [1:0] state);

`define S0  2'd0
`define S1  2'd1
`define S2  2'd2

reg [1:0] state_nxt;

always @(posedge clock or negedge resetn) 
         if(!resetn) state <= `S0;
         else state <= state_nxt;


always@(*) begin
state_nxt = state;
case(state)
     `S0:                    state_nxt = `S1;
     `S1:                    state_nxt = `S2;
     `S2:                    state_nxt = `S0;
     default:              state_nxt = `S0;
endcase
end

endmodule