Queues

In SystemVerilog, queues provide a powerful and flexible way to manage collections of data. They are similar to dynamic arrays in the sense that they can grow and shrink during runtime. However, queues offer additional capabilities that make them even more flexible and useful in a range of scenarios.

Declaration and Usage

A queue is declared similarly to a dynamic array, with the datatype of the elements it will hold, followed by the name of the queue and an empty set of square brackets:

datatype queue_name[];

For example, to declare a queue of integers:

integer my_queue[];

You can add elements to the queue using the push_front or push_back methods:

my_queue.push_back(5);  // Adds 5 to the end of the queue
my_queue.push_front(10); // Adds 10 to the start of the queue

You can also remove elements from the queue using the pop_front or pop_back methods:

my_queue.pop_front(); // Removes the first element from the queue
my_queue.pop_back(); // Removes the last element from the queue

Accessing elements in a queue is done by using the index, just like with arrays:

$display(my_queue[0]); // Will display the first element in the queue

Characteristics and Use Cases

Queues are highly versatile and can be used as stacks (LIFO: Last In, First Out), queues (FIFO: First In, First Out), or lists where you can insert and delete elements at any position. Their ability to automatically manage the size of the collection makes them ideal for dealing with variable amounts of data, such as storing a varying number of test results or processing a list of events in a simulation.

However, queues also have some performance overhead due to their flexibility. It's best to use them when their unique capabilities are required, and simpler structures like fixed-size arrays or dynamic arrays won't suffice.

Up next, we will delve into the various operations and methods that you can perform on queues in SystemVerilog to harness their full potential.