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Verilog Initial stmts IF-ELSE Case stms Readmemh Function Testbench Binary to Gray Clock Crossing Half-adder Full-adder Tristate buffer Adder tb Counter_enable Blocking Operators Shift LSR Random Nos Sync RAM Verilog Tutorial

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Verilog Tutorial.
Digital Basics Tutorial.
Verilog code to Function call and Declaration.  
/*Verilog functions are discussed here.*/
reg [5:0] counter_binary, counter_binary_reg, counter_gray, counter_gray_reg;
integer count, file_wr;
/*Function Declaration: Gray from Binary code*/
function[5:0] binary2gray ;
   input[5:0] value;
   integer i;

        binary2gray[5] = value[5];
       for (i=5; i>0; i = i - 1)
           binary2gray[i-1] = value[i] ^ value[i - 1];
//Function call
always @(*)
counter_binary = counter_binary_reg;
counter_gray = binary2gray(counter_binary_reg);
end .............
Check the complete usage of the function in following verilog example
Verilog Function declaration and call.
Interview Questions. Main, FPGA, Digital Fundamentals
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Return to Verilog Tutorial
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Verilog functions are used to simplify coding in presence of lengthy, complex and repetitive code. Functions are used to group code segments which can then be used multiple (no limit) times. Terms used in example code below are Function Declaration and Function Call.     

Properties of functions:

(1) Can only be used to pass one argument to/from function.

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Interview Questions. Main, FPGA, Digital Fundamentals
Interview Questions. Main, FPGA, Digital Fundamentals

(2) Function code segments with latches will not get interpreted during synthesis. So avoid latches in function code to prevent simulation/synthesis mis-match. (3) A function can only be called from an “always” code block. For test benches its also allowed from within “initial” blocks. (4)  Never use delay, event or timing control in functions. (5) Wires are not allowed in verilog functions.

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