Posted by Mike Thompson on November 26th, 2012
Well of course that depends on what you are talking about. In the world of microprocessors size does matter. Not only does size equate to cost, but also to power consumption. Depending on the design that you are doing both can be major considerations. There can also be size considerations for the amount of memory that will be used with the processor making code density a critical parameter. If the only thing that you care about in a design is performance then size maybe doesn’t matter, but then again maybe it does. It used to be that I would have customers tell me that performance is all that mattered. I don’t hear that so much anymore – in fact it is rare.
For processors that are designed for embedded and deeply embedded applications size and power more often than not are the main requirements. That a processor can run at 500 MHz doesn’t matter so much if you are only planning on clocking it at 10 MHz, but size gets really important if the application is a sensor and you are planning to put it in a 2×2 mm package. As small as that is power consumption can be even more challenging. I have seen specifications for sensors where 100uW is the total power available for the whole sensor. When you consider that this level of power could easily be consumed by leakage it becomes apparent that the total sensor implementation has to be very small. This takes a special breed of microprocessors that are designed from the ground up to be implemented to minimum size and power, but also with excellent instruction performance to minimize the memory requirements.
With this in mind Synopsys developed the EM family of 32-bit processors. Designed for sensor and embedded control applications the cores start at fewer than 10K gates and can be quickly configured to a specific application, so that no gates are wasted. This is especially important at the older process nodes where many of the sensor and control applications are being implemented and each additional gate takes a lot more area and power.
The EM processor family has also been designed to reduce the memory footprint offering 20% better code density, which reduces power consumption and leakage. It is not unusual for the memory that is attached to a processor to take more area than the processor. A 20% reduction in the amount of memory needed for an application can be very significant, especially when area and power are limited.
Performance is still important in many applications, but more and more power and size are dominating processor selection criteria. Whether it is to increase battery life or reduce the operating cost of an application the size of a processor and the memory that it requires matters, and this will be increasingly true as we move forward.