Thread: What is a "callback" in Systemverilog?

Could someone explain "callback"? I hear this term mentioned in the Synopsys VMM guide, and Chris Spear's Systemverilog for Verification.

Is a callback a special type of function/task call? Or is it just a fancy name for regular function/task call that is stored in a class?

Suppose if you are doing transmitting data using mailboxes, Once you are send ing data to design from genetarator . The same data you need to put back in score board for latter comparison. This is called callbacks

In VMM we have methods for call back .

Originally Posted by boardlanguage

Could someone explain "callback"? I hear this term mentioned in the Synopsys VMM guide, and Chris Spear's Systemverilog for Verification.

Is a callback a special type of function/task call? Or is it just a fancy name for regular function/task call that is stored in a class?

It is built on SV virtual task/function, but wrapped in a facade class. It is a standard OOP pattern, google search reveals good explanation, see:

http://www.berczuk.com/pubs/PLoP94/callback.html

In our VMM adoption book, we have shown few worked out examples of callback usage for HW verification. I also cover this as part of my VMM class in Bangalore.

HTH
Ajeetha, CVC
www.noveldv.com

As per Systemverilog Perspective,

Callbacks generally used to store expected data and check DUT Data against expected data. These call backs are called before transmitting and after receiving data.

Added after 54 seconds:

As per Systemverilog Perspective,

Callbacks generally used to store expected data and check DUT Data against expected data. These call backs are called before transmitting and after receiving data.

the "callback" method is to keep the data transmite and receive more accureate!

We may have to create a verification environment that can be used for all the tests. Test program should be able to inject new code without modifying original classes. Any change in the transaction(like injecting errors, inserting delays, synchronizing this transaction with others, put the transaction in scoreboard, gather functional coverage data) can be achieved by “callback” routine without changing the original classes.
The callback task is created in the top level test and called from the driver, lowest level of environment.

Callbacks are used by tests to add new functionality to the driver without editing the driver class. Following types of new functionality can be added using callbacks:

􀂄 Inject errors
􀂄 Drop the transaction
􀂄 Delay the transaction
􀂄 Synchronize this transaction with others
􀂄 Put the transaction in the scoreboard (for data comparison as explained by friends above)
􀂄 Gather functional coverage data