For many years, people have been talking about configuring processor IP cores, but especially with growing interest in the open RISC-V ISA, there is much more talk about customization. So, processor configuration vs. customization: what is the difference?

CPU configuration is like ordering a pizza from the pizzeria

A simple analogy is to think of ordering a pizza. With most pizzerias, you have standard bases and a choice of toppings from a limited list. You can configure the pizza to the sort of taste you would like based on the standard set of options available.

Processor IP vendors have typically offered some standard options to their customers, such as optional caches, tightly coupled memories, and on-chip debug, so that they could combine them and provide the customers with suitable configurations for their needs. While doing so, the core itself remains the same, or has very limited variations. Certainly, the instruction set, register set, and pipeline would remain the same, and only optional blocks such as caches are allowed to vary.

CPU customization is like having a chef making a special pizza for you

Today, many users are demanding greater specialization and variability in their processor cores. This may be to achieve enhanced performance while keeping down silicon area and power consumption. There may be a number of ways in which this can be achieved, for example, by creating custom instructions optimized to the target application, adding extra ports and registers. Such changes fundamentally alter the processor core itself.

Returning to the pizza analogy, customization is like if a private chef has an underlying pizza base recipe but is willing not only to let you provide alternative toppings, but to modify the pizza base, with alternatives to the standard flour, oil, and yeast ingredients used. This is quite a good reason why you would want to customize a processor, isn't it!

And this is exactly what RISC-V allows you to do. You can customize an existing RISC-V processor to meet your specific requirements by adding optional standard extensions and non-standard custom extensions.

Create a custom core with RISC-V and Codasip

Although some proprietary IP suppliers allow their cores to be extended, the greatest customization opportunity lies with RISC-V. The ISA was conceived from the outset to support custom instructions. Codasip’s RISC-V processors were developed using the CodAL architecture description language and are readily customized using Codasip Studio. For more information on how custom instructions can be used to create domain-specific processors, download our white paper.