Monday, May 23, 2016

.....of Errors & Mistakes in Verification

Miniaturization of devices has led to packing more functionality on the given slice of silicon. An after effect of that is heating of the device due to increased power consumption and discovering innovative ways of cooling off these components. As electronics adopted wireless, the concern on power came to forefront as, who wants to recharge the battery every second hour. Different techniques have been adopted since then to address this growing concern. One such technique is letting parts of silicon go to into hibernation and trigger a wake up when needed. My hibernation from blogging was no different except that though I received many pokes during this time probably the trigger wasn’t effective enough to tantalize the antennas of the blogger in me. It was only during a recent verification event hosted by Mentor Graphics when my friend Ruchir Dixit, Technical Director – India at Mentor Graphics introduced the event with an interesting thought touching the basics of verification. The message completely resonates the idea of this blog of exploring verification randomly but rooted on basics and I took it as a sign to get the ball rolling again. To start with, I am sharing the thoughts that actuated this restart. Thank you Ruchir for allowing me to share the same.

Source: Slides from Ruchir Dixit - 'Verification Focus & Vision' presented at Verification Forum, Mentor Graphics, India

Before we unfold the topic further have you ever thought as to why computers only spell out ERRORS & not MISTAKES?

Let’s start with understanding the basic difference between an error & a mistake. A mistake is usually a choice that turns out to be wrong because the outcome is wrong. Mistakes are made when a free choice is made either accidentally or performance based but can be prevented or corrected. An error, on the other hand, is a violation of a golden reference or set of rules that would have lead to a different action and outcome.  Errors typically are a result of lack of knowledge and not choice. That is the reason that computer doesn’t make mistakes and only throws error on screen when unable to move forward on a pre-defined set of actions or sees a violation to them. And that is again a reason why you see Warnings & Errors from our EDA tools and not Mistakes :) Machines don’t make mistakes… we do!

Now talking about verification, the sole reason of why we verify is BUGS! And the source of these BUGS are the ERRORS & MISTAKES committed as part of code development.

Mistakes as we understood earlier is resultant of a free choice. While no one wants to make a bad choice, still this creeps into the code due to distractions or coding in a hurry. To prevent or correct such mistakes it is the basic discipline one needs to follow and that is where the EDA tools come to rescue in assisting you to make the right choice.
Errors typically happen due to ignorance about the subject or partial knowledge leading to wrong assumptions. This could further find it roots in incomplete documentation or incorrect understanding of the subject. Given that documentation & the resulting conclusions are more subjective it is hard to define the right way to document anything. The only way to minimize errors is to prevent them from occurring by defining clear set of rules that need to be followed and that is where ‘Methodology’ comes into picture. A classic example of the same is having a template generator for UVM code to ensure the code is correct by construction & integrates seamlessly at different levels. Having coding guidelines is another way to reduce errors. Uncovering the rest of the errors is where the tests become important and unless we stimulate that scenario we may not know what & where the error is.

So while errors & mistakes are unavoidable, it is the deployment of the right set of methodologies and tools that leads to a bug free silicon …. In time…. Every time!

After writing this post, I was tempted to say that ‘To ERR is HUMAN and to FORGIVE or VERIFY is DIVINE! 

But then that would be a MISTAKE again :)

Happy Bug Hunting!!!

Disclaimer: “The postings on this blog are my own and not necessarily reflect the views of Aricent”

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