Recently while reviewing a test bench architecture with a group of verification engineers, an inveterate though interesting debate started. The engineer proposing the verification plan had ‘scoreboard’ as well as ‘checkers’ as two different components in his test bench. The debate was on the clear definition of these 2 terminologies as every engineer had his own understanding of these words. Though various verification methodologies have termed the test bench components differently, still names like driver, bfm, generator and sequencer etc. reveal a lot about their functionality with the exception of scoreboard. Engineers across the globe have varied opinion on the history of this term and its origin as a verification component is untraceable.
Here is a quick preview of the various definitions of ‘what is a scoreboard’?
A scoreboard is a large board in a ballpark, sports arena, or the like for publicly displaying the score in a game or match and often other statistics, such as the count of the balls and strikes etc.
A scoreboard is a centralized hardware mechanism (initially used in CDC 6600 – 1964) used to keep a track on the activity (instructions being fetched, issued, executed etc. and the resources they use) inside a system that helps in determining certain decisions (dynamically scheduling instructions). Here the activities are tracked by flipping bits in scoreboard that keep a score of what is going on in the system.
These definitions are relevant to the scoreboard usage in verification. There are examples of primitive test environment where testing as an activity was maintained using an array of registers (scoreboard) representing tests to be executed. The registers would maintain if a test ran and the status of the result. On completion of the test suite the scoreboard would help generate the statistics and determine next steps. Scoreboard however has evolved from tracking & decision making into multiple avatars wherein it can be as simple as a data structure or as complicated as having the transfer function (predictor) and compare function included. So far in my experience I haven’t seen scoreboards performing protocol compliance checks so I believe my colleague was right in proposing scoreboard as an entity, predicting and comparing while the protocol checks to be handled by a separate component he referred to as checker.
These definitions are relevant to the scoreboard usage in verification. There are examples of primitive test environment where testing as an activity was maintained using an array of registers (scoreboard) representing tests to be executed. The registers would maintain if a test ran and the status of the result. On completion of the test suite the scoreboard would help generate the statistics and determine next steps. Scoreboard however has evolved from tracking & decision making into multiple avatars wherein it can be as simple as a data structure or as complicated as having the transfer function (predictor) and compare function included. So far in my experience I haven’t seen scoreboards performing protocol compliance checks so I believe my colleague was right in proposing scoreboard as an entity, predicting and comparing while the protocol checks to be handled by a separate component he referred to as checker.
Later that day while reading an intriguing article on context aware applications I came across this definition of context which states that –
“Context is any information (the parts of a written or spoken statement that precede or follow a specific word or passage, usually influencing its meaning or effect) that can be used to characterize the situation of an entity. An entity is a person, place, or object that is considered relevant to the interaction between a user and an application, including the user and applications themselves.”
With the dilemma on the real intention of the user who coined this word (scoreboard) in verification domain or where it was first used I could only conclude that the definition of scoreboard is relative to the context it is used in. The context could be a methodology that defines this term clearly or the test bench architecture where it is used. If you know the functionality of the other components in the test bench (which you can fairly conclude by their names) the rest can be assumed to be taken care by scoreboard J
Check out what Scoreboard means in UVM @ verification academy.
Drop in a comment to share your experiments with the scoreboard definitions!
