Parbegin / Parend Concurrent Statement

In hardware description languages like VHDL, a "parent" concurrent statement is used to establish a hierarchical design structure. It enables the creation and management of several processes within of a single organization.

An illustration of a parent concurrent statement is as follows −

entity my_entity is
   port (
      clk: in std_logic;
      reset: in std_logic;
      data_in: in std_logic_vector(7 downto 0);
      data_out: out std_logic_vector(7 downto 0)
   );
end entity;
 
architecture behavioral of my_entity is
begin
   -- Parent Concurrent Statement
   parent_process: process(clk, reset)
   begin
      if reset = '1' then
         -- Reset condition
         data_out <_edge(clk) then
         -- Child process 1
         child1_process: process(data_in)
         begin
         -- some logic using data_in
         data_out(0) <= data_in(0);
         data_out(1) <= not data_in(1);
         end process;
            
         -- Child process 2
         child2_process: process(data_in)
         begin
         -- some logic using data_in
         data_out(2) <= data_in(2);
         data_out(3) <= not data_in(3);
         end process;
      end if;
   end process;
end architecture;

A parent process with the name parent_process exists in the code above. Changes in the clk and reset signals start this process.

The data_out signal is set to zero if the reset signal is strong. Two child processes, child1_process and child2_process, are formed when the reset signal is low and clk has a rising edge.

Each of the two child processes is started when the data_in signal changes. They use data_in to do some processing and give values to particular bits of the data_out signal.

Stepwise Execution of the Code

• Input and output ports are defined for the entity my_entity.

• The parent process is created and given the name parent_process according to the architectural behavioural definition.

• The signals clk and reset cause the parent process to run.

• The data_out signal is set to zero if the reset signal is strong.

• Two child processes, child1_process and child2_process, are formed when the reset signal is low and clk has a rising edge.

• Data_in is used by the child processes to execute some logic when the data_in signal changes.

• particular bits of the data_out signal.

• Until another triggering event happens, the parent process continues to run the code.

How to construct a Parend concurrent statement?

A concurrent programming concept called parbegin enables several activities or processes to run simultaneously. It separates the code into sections that can run concurrently and independently. Depending on the platform or programming language being used, parbegin's specific behaviour may change. If parbegin is used carelessly, it may result in race situations and other concurrency problems.

The keyword "generate," which is followed by a label and enclosed by the keywords "begin" and "end," designates the parent concurrent statement. "If" statements, "for" loops, and "case" statements are additional concurrent statements that can be introduced. An illustration of a parent concurrent statement is the following −

Syntax

gen_label: generate
   for i in 0 to 3 generate
      process_clk: process (clk)
      begin
         if rising_edge(clk) then
         -- do something
         end if;
      end process process_clk;
   end generate gen_label;

Advantages and Disadvantages of Parend concurrent statement

Parent concurrent statements provide a lot of benefits, but there are also some possible drawbacks that designers need to be aware of. Using parent concurrent statements may have the following drawbacks −

Disadvantages

Timing problems

Timing dependencies between concurrent operations can be challenging to handle. One process might need to wait for another process to finish before it can begin, for instance, if it depends on the output of another process. To guarantee proper operation, these temporal restrictions may be introduced and must be carefully managed.

Increased resource consumption

Multiple processes running at once can use up more memory and processor time. The design may use more resources overall if there are many more procedures than necessary.

Limited parallelism

While parent concurrent statements permit the execution of processes in parallel, the amount of parallelism may be constrained by the hardware resources at hand. Some concurrent processes might need to be serialized if there are insufficient hardware resources to support them all, which would reduce the potential advantages of parallel processing.

Problems with debugging a design with several concurrent processes

Complex interactions between the processes might make debugging difficult. If a problem involves interactions between several processes, it could be challenging to pinpoint its root cause.

Overall, parent concurrent statements have a lot of advantages, but they can also add some extra complexity and difficulties that need to be carefully handled. When deciding whether to use parent concurrent statements in a given design, designers should carefully consider the benefits and drawbacks of doing so.

Advantages

A concept used in the design of digital circuitry called a parent concurrent statement enables numerous processes to run simultaneously. Parent concurrent statements have the following benefits −

Parallel execution

Parent concurrent statements enable the parallel execution of numerous processes. The ability to do several jobs at once can enhance the design's overall performance.

Modular design

Parent concurrent statements enable a modular design approach in which various design components can be executed as independent processes. As a result, it may be simpler to manage intricate and large-scale designs since every step may be designed and tested separately.

Better readability

Designers can make their code more understandable and maintainable by employing parent concurrent statements. Due to the fact that each process may be built as a separate module with a distinct interface and well-specified inputs and outputs, this is possible.

Better fault isolation

Parent concurrent statements can aid in better fault separation in a design. It is less likely that a malfunction in one process will have an impact on concurrently running processes.

Simplified debugging

Debugging can be made simpler by employing parent concurrent statements in a design. It is possible to test and debug each process independently, which can speed up the identification and isolation of issues.

All things considered, parent concurrent statements are a potent tool for digital hardware designers, offering a number of advantages that can help to enhance performance, readability, and maintainability of designs.

Example

A concurrent statement in VHDL is one that runs alongside other statements in the design simultaneously. A concurrent statement that uses brackets to aggregate several other concurrent statements together is known as a parenthesized concurrent statement. Here is an illustration of a parenthesized concurrent statement written in VHDL.

begin
S1;
      parbegin
      S3;
      begin
      S2;
         parbegin
         S4;
         S5;
         parend;
         S6;
      end;
      parend;
S7;
end;

Output

The three concurrent statements in this example will all run simultaneously because they are surrounded in brackets. A process in the first sentence starts when clk's leading edge rises. The second sentence gives my_signal a "1" value when my_condition is true and a "0" value otherwise. My_output is given my_input + 1 in the third statement.

It's crucial to remember that the brackets themselves have no bearing on how the concurrent statements behave. Simply for the sake of organization and readability, they bundle the sentences together.

Conclusion

A sort of statement used in VHDL that enables the grouping of numerous concurrent statements within a set of brackets is known as a parenthesized concurrent statement. This might make the design simpler and easier to comprehend and maintain. As with every VHDL construct, it is crucial to use it properly and comprehend its restrictions and dangers.A concurrent statement allows for the specification of simultaneous processes in a hardware design without the need for sequential code constructs like loops or if-else statements, making it a significant component of hardware description languages. By enabling many activities to take place at once, this can enhance the design's performance and efficiency. It enables the construction of parallel blocks that can aid in the modularization of complex behaviour and interact with one another via shared variables or signals.