Verilog procedure assignment statement

initial、always

• A module can contain multiple initial and always sentence , but 2 Statements cannot be nested .
• These statements are executed in parallel between modules , It has nothing to do with the sequence before and after the module .
• however initial Sentence or always The inner part of the statement can be understood as sequential execution （ Except for non blocking assignment ）.
• Every initial Sentence or always Statements will produce an independent control flow , The execution time is from 0 The moment begins .

initial sentence

• initial Statements from 0 Start at every moment , Only once , Multiple initial Blocks are independent of each other .
• If initial The block contains multiple statements , Keyword required begin and end Form a block statement .
• If initial There is only one statement in the block , keyword begin and end It can be used or not .

always sentence

And initial On the contrary ,always Statements are repeated .always Statement block from 0 Start executing the behavior statement at any time ; When the last statement is executed , The first statement in the statement block is executed again , This cycle is repeated .

Due to the characteristics of loop execution ,always Statements are mostly used to simulate clock generation , Detection of signal behavior, etc .

  Blocking assignment and non blocking assignment

Block assignment

Block assignment belongs to Sequential execution , That is, before the execution of the next statement , The current statement must be executed .

Blocking assignment statements use the equal sign  =  As an assignor .

In the previous simulation ,initial The assignment statements inside are blocking assignment .

Nonblocking assignment

Non blocking assignment belongs to Execute statements in parallel , That is, the execution of the next statement and the execution of the current statement are carried out at the same time , It does not block the execution of subsequent statements in the same statement block .

Non blocking assignment statements use the less than or equal sign  <=  As an assignor .