or should be statement statement_group) executed. If the loop condition expression is true, the loop is entered. The final expression is evaluated at the end of the loop. (step) Syntax begin: accumulate disable forever group_name; It discontinues execution of a named group of @(posedge clk); disable statements. a = a + 1; if (a == 2’b0111) disable accumulate; end end FUNCTION and TASK 3. Verilog provides Functions and Tasks to allow the behavioral description of a module to be broken into more manageable parts allowing better readability and manageability. Functions and Tasks are useful for several reasons which are, they allow often used behavioral sequences to be written once and called when needed, they allow for a cleaner writing style and finally they allow data to be hidden from other parts of the design. 3.1 FUNCTION Functions are defined in the module in which they are used. It is possible to define function in separate file and use compile directive 'include to include the function in the file which instantiates the function. Function can call other functions, but cannot call task. The following are some of the general rules for functions: Functions must contain at least one input argument and cannot drive more than one output. Functions cannot contain an inout or output declaration. Functions cannot contain time controlled statements (#, @, wait), i.e., it cannot contain delays . Function cannot include timing delays, like posedge, negedge, # delay. Which means that function should be executed in "zero" time delay. Functions must contain a statement that assigns the return to the implicit function name register. The variables declared within the function are local to that function. The order of declaration within the function defines how the variables passed to the function by the caller are used. Syntax
statement or statement_group) should be executed. If the loop condition expression is true, the loop is entered. The final expression (step) is evaluated at the end of the loop. disable Syntax disable group_name; It discontinues execution of a named group of statements. begin: accumulate forever @(posedge clk); a = a + 1; if (a == 2’b0111) disable accumulate; end end 3. FUNCTION and TASK Verilog provides Functions and Tasks to allow the behavioral description of a module to be broken into more manageable parts allowing better readability and manageability. Functions and Tasks are useful for several reasons which are, they allow often used behavioral sequences to be written once and called when needed, they allow for a cleaner writing style and finally they allow data to be hidden from other parts of the design. 3.1 FUNCTION Functions are defined in the module in which they are used. It is possible to define function in separate file and use compile directive 'include to include the function in the file which instantiates the function. Function can call other functions, but cannot call task. The following are some of the general rules for functions: Functions must contain at least one input argument and cannot drive more than one output. Functions cannot contain an inout or output declaration. Functions cannot contain time controlled statements (#, @, wait), i.e., it cannot contain delays . Function cannot include timing delays, like posedge, negedge, # delay. Which means that function should be executed in "zero" time delay. Functions must contain a statement that assigns the return to the implicit function name register. The variables declared within the function are local to that function. The order of declaration within the function defines how the variables passed to the function by the caller are used. Syntax
training_manual_for_fpga_programming_using_verilog_hdl_language.docx