Operator, assignment statement, structure description statement

Logical operators

An operator （& | ~）       

Logical operators （&&  ||  ！）

Relational operator

<   >   <=   >=

Equality operators

==（ be equal to ）  ！=（ It's not equal to ） ===（ be equal to ） ！==（ It's not equal to ）

Reverse sign 、 Double equal sign 、 There must be no space between the three equal signs .

=== When operating , Compare the indefinite value and high resistance value of some bits , Only when it is exactly the same, the result is 1（1、1,0、0,x、x,z、z） Commonly used in case The discrimination of expression

== When operating , At least one x、z when , The result is x

Shift Operators

Move left n position a<<n              Move right n position a>>n

Note that the operand is on the left ,n How many positions does the representative move , The vacated space is used 0 fill

Bit concatenation operator

Some bits of two or more signals are spliced together for operation , Signals without specified digits are not allowed in expressions

{a,b[3:0],4{w}}        // When repeating an expression , Must be preceded by a constant expression

Reduction operator

Monocular operator , There are also and or not . It is an and or non recursive operation on a single operand , The final result is 1 The binary number of bits .

reg [3:0] B;
reg C;
    C=&B;    // Be similar to C=（（B[0]&B[1]）&B[2]）&B[3]

Operator precedence

Assignment statements and block statements

Nonblocking assignment （b<=a）

• In the block , The assignment of the above statement cannot be immediately used by the following statement
• The assignment operation can be completed only after the end of the block , And the assigned variable value is obtained from the last assignment
• When writing integrable sequential logic modules , Is the most commonly used assignment method

In a serial statement , There is no priority for non blocking assignment statements , The first one will not affect the execution of the following statements , Each statement is executed in parallel ; Executing a non blocking assignment statement will first calculate the value of the right-hand expression , Then wait for the delay time to end , Then assign the calculated value to the variable on the left .

Block assignment （b=a ）

• After the execution of the assignment statement , That's the end of it
• b The value of is changed immediately after the assignment statement is executed
• Using it in temporal logic will produce unexpected results

In a serial statement , Blocking assignment statements will be executed in order ; Each blocking assignment statement in the parallel statement is executed at the same time ; Blocking assignment evaluates the expression to the right of the equal sign , Then assign it to the left immediately

/* Nonblocking assignment can be seen as two steps , The first step is to calculate the value on the right , Update to the left after completion */
[email protected](posedge clk)    
    begin
        b<=a;
        c<=b;  //c Original b value 
    end

Block statement

Combine multiple statements together , Make it look more like a statement in format .

Sequential block

begin_end, Identify statements executed sequentially .

• The statements in the block are executed sequentially
• The delay time of each statement is relative to the simulation time of the previous statement
• Until the last statement is executed , Program flow control just jumps out of the statement block

-> end_wave //-> Indicates trigger event end_wave Turn it over

begin: Block name         // Block name , An identification name ,
     In block declaration statements    // Such as parameter declaration statement 、reg Type variables declare variables 、real Type variable declaration 
     sentence 1;
     sentence 2; 
     sentence n;
end

Parallel blocks

fork_join, Identify statements executed in parallel .

• Block statements are executed at the same time
• The delay time of each statement in the block is relative to the simulation time when the program flow control enters the block
• Delay time is used to provide execution timing for assignment statements
• When sorted in chronological order after the last statement is executed or after a disable Statement execution , Program flow control jumps out of the program block

An in block declaration statement can be a parameter description statement 、reg、integer、real、time Type variable declaration statements and events （event） Statement of explanation .

Block name

• You can define local variables within a block
• You can allow blocks to be called by other statements , Such as disable
• Verilog All variables in are static , That is, all variables have only one unique storage address , So entering or leaving a block does not affect the value stored in the variable

（ The block name provides a way to confirm the value of a variable at any simulation time ）

Start time and end time