Friday, 25 September 2009

"Transmute" - Design Philosopies

I realized that I had forgotten to describe a very, very important step: Philosophy. In this case I am using the word incorrectly. It is actually World View that I mean. From Wikipedia:
"A comprehensive world view (or worldview) is the fundamental cognitive orientation of an individual or society encompassing natural philosophy, fundamental existential and normative postulates or themes, values, emotions, and ethics."
Now what has this to do with chip design? Well you might ask! In this case it is the fundamental underpinnings and assumptions that surround the design.

The world view is formed from facts and opinions and our emotional reaction to them.

So here is the list of suitable facts for the "Transmute" project:
  • We have only built cell based custom digital cores
  • None of our typical projects are as large as this
  • The design flows are not stable - considerable development will be required
  • Several custom digital modules will be required to interfaced to licensed IP
  • We can experiment with power saving strategies
  • We are very experienced with custom analogue blocks
What, as a designer, is my emotional reaction to this? Simply this: Excitement and Concern. There are a lot of unknowns.

Hence our design World View (although a different design will have a different world view):

  • Digitally Conservative
  • Analogue Progressive
One you articulate this World View clearly you realize that this is the guide for your choices, in our case:
  • Hard IP: Eliminates the risk from core synthesis
  • Digital part to be separable from the analogue part so we can drive them separately. This will minimize the cost in case of failure or error - we would get at least one working part from the chip
  • Digital power saving strategies to be applied only after a high confidence in non-power saving digital structures obtained
  • It must be possible to disable the digital power saving structures if they are added
  • Flow decisions should favour tools which we have experience with
These decisions then guide the rest of the design flow. Also new choices can be matched against the worldview ensuring consistency.

Just bear in mind, your world view for this design may need modifying as the project progresses however if it does then you need to reconsider most of the work you have already carried out. This is typically far more important if your original plan was aggressive and you move to conservative - check work and assumptions already made!

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