Wednesday, April 18, 2012

SVA : System Verilog Assertions - Dynamic Control Methods to control Assertions

Dear AwA Readers,

System Verilog assertions are becoming popular now a days and industries are adopting SVA as part of their verification environment. SVA (System Verilog Assertions) are useful in many areas in design as well as in Verification. There has been a debate going on since long on "Who should write assertion designer or verification engineer ?" This question inspired me to write on blog post to discuss this point, you can refer my blog post on 'Who should write SVA?'

Well, here I would like to discuss SVA control mechanism which will answers your question "How to control SVA dynamically?"

One of the biggest issue with Verilog type Assertion is that they are either always on or through `defines, set to be always off. They could not be turn ON or OFF dynamically. System Verilog Assertions have resolved this issue by adding system functions called $assertoff, $asserton and $assertkill.

Definition :
1. $assertoff:
This system function is used to disable all assertions but allows currently active assertions to complete before being disabled.
2 $asserton:
This system function is used to turn all assertions back on
3. $assertkill:
This system function used to kill and disable all assertions including currently active assertions.

By using $assertoff, the assertions specified as argument of this function will be turned off until a $asserton is executed. This way you can control assertions dynamically. Isn't it interesting ? It is !! I have used these feature in one of my project years back and realized it's beauty. Using these system tasks you can make your assertions dynamic and based on need and requirement you can make them enable or disable. You can even kill using $assertkill all assertions if you dont want to run them during your simulation. Wow !!!! Isn't it a real beauty?, Engineers are now super flexible to use and control the SVAs :)

Dynamic control of Assertions can be used to turn off assertions during reset and initialization or during simulation erroneous protocol behavior.

I had a situation where I had to shut off all my assertions and let my simulation run to cover some of my interesting and robustness types of scenarios. You might have situations where you might need to shut off your all implemented assertions or some particular assertions during your simulation. SVA allows us to use these system functions and we can play around with these system to have full control on Assertion ON-OFF or event to kill all assertion in some cases.

Have fun with SVA (System Verilog Assertions) and use its super functionality with user friendly control !!

ASIC With Ankit

1 comment:

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