Introduction to Looping Constructs

Introduction to Looping Constructs

Looping constructs are VHDL instructions that allow a program to repeat the same block of code, a process known as iteration (similar to C).

Loops in VHDL are divided into two main categories based on how they function and what they create.

1. Sequential Loops (Inside a process)

These loops are similar to those in traditional programming languages. They describe an algorithm or a sequence of operations that execute step-by-step.

• They can only be used inside a process, function, or procedure.
• They are synthesized into hardware that performs an operation over multiple clock cycles or as a large block of combinational logic.

There are two main types of sequential loops:

• for loop -> Repeats for a specific number of times. Use this when you know the exact number of iterations.

• while loop -> Repeats as long as a certain condition is true. Use this when the number of iterations is unknown.

2. Concurrent Loops (Outside a process)

This type of loop is unique to hardware description languages. It doesn't describe an algorithm but instead describes the replication of hardware structures. It acts like copy and pasting ICs on a breadboard.

(well, that's the gist of it)

• It creates multiple instances of concurrent statements (like component instantiations).

• It is only used outside of a process, in the main architectural body.

• The main type is the for-generate loop.