Testbench Fundamentals

Abstract

To answer does-it-work questions, we need to stimulate the design with known stimulus and determine if the design responds as intended. That is, we need to control and observe the DUT.

Two of the most fundamental objects in testbenches are drivers and monitors. A driver converts a stream of transactions into activity on a pin-level interface. A monitor does the opposite; it converts activity on a pin-level interface into a stream of transactions. Drivers are used to control the DUT by applying stimulus, and monitors are used to observe the responses.

To understand how to build and use drivers and monitors, we will start with a transaction-level example that illustrates a stimulus generator (memory master) connected with a memory slave. The memory slave is a stand-in for a driver. Whereas a true driver has a pin-level connection, the memory slave does not. What the memory slave and driver have in common is that their transaction interfaces and their internal architecture are the same. After building an understanding of the transaction-level example, we will expand it to use pin-level communication.