Nios II Custom Instruction User Guide

ID 683242
Date 4/27/2020
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2.1.5. External Interface Custom Instructions

Nios II external interface custom instructions allow you to add an interface to communicate with logic outside of the processor’s datapath.

At system generation, conduits propagate out to the top level of the Platform Designer system, where external logic can access the signals. By enabling custom instruction logic to access memory external to the processor, external interface custom instructions extend the capabilities of the custom instruction logic.

Figure 9. Custom Instruction with External Interface

Custom instruction logic can perform various tasks such as storing intermediate results or reading memory to control the custom instruction operation. The conduit interface also provides a dedicated path for data to flow into or out of the processor. For example, custom instruction logic with an external interface can feed data directly from the processor’s register file to an external first-in first-out (FIFO) memory buffer.