Posts Tagged ‘performance margins’

Designing a Chip for Unplanned Products

Wednesday, December 29th, 2010 Gary Stringham

One of the rules of the Extreme Programming design philosophy for software is Never Add Functionality Early. This means that when coding for one product, do not add features or functionality needed for a future product. While this rule does have some merit for software development, it should be applied more judiciously to hardware development.

One of the reasons programmers can get away with that type of thinking is because they can and are able to change software rapidly by simply recompiling and re-executing. Hardware engineers do not have that luxury. It takes months and millions of dollars to produce a different version of the chip. Future costs can be reduced if the chip is designed with the future in mind, with the possibility that it might be used in future products that are currently unplanned.

There is also an aspect of planning for the future where you prepare by building a framework but not putting in the features. That makes it easier to implement the new features in the future but still requires putting out a new version of the chip. But that will be the subject for another issue. For this issue, I am talking about what can be done to make this version of the chip more likely to be used in the future.

Not all known future functionality should be put into the design; time, effort, space and cost will not permit it. But some of it has little risk in terms of complexity, implementation and verification. If a three-bit number might need four bits in the future, making it a four-bit number now has little risk to the program. Adding a couple of extra GPIO lines is also low-risk (assuming there are pins for it.) Adding a block that is new, big and complex could add a lot of risk to the program and needs to be weighed against the potential gain if it were needed.

Extreme Programming says that “only 10% of that extra stuff will ever get used.” But if you put 10 “extra” features in the chip and only one gets used, you could save your company months and millions of dollars.

Best Practice: Include low-risk features in the design of the chip that might be used in future products.

Aside from features that might be needed in the future, faster speed is characteristic of future products. Chips are designed with a performance and speed budget. Planning for the future would mean that you also look at the speed of the chip. I have seen cases where existing chips were limited in their usefulness because they were not fast enough and we had to spend lots of time and money to produce a new version just to get the speeds we needed.

Best Practice: Increase the performance margins in the design to allow the chip to be used in faster products in the future.

Always looking toward the future…