1. Nios II Custom Instruction Overview
Custom instructions give you the ability to tailor the Nios II processor to meet the needs of a particular application. You can accelerate time critical software algorithms by converting them to custom hardware logic blocks. Because it is easy to alter the design of the FPGA-based Nios II processor, custom instructions provide an easy way to experiment with hardware-software tradeoffs at any point in the design process.
The custom instruction logic connects directly to the Nios II arithmetic logic unit (ALU) as shown in the following figure.