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4.3.1. Writing the Custom Instruction HDL File
4.3.2. Opening the Component Editor
4.3.3. Specifying the Custom Instruction Component Type
4.3.4. Displaying the Custom Instruction Block Symbol
4.3.5. Adding the Custom Instruction HDL File
4.3.6. Configuring the Custom Instruction Parameter Type
4.3.7. Setting Up the Custom Instruction Interfaces
4.3.8. Saving and Adding the Custom Instruction
4.3.9. Generating and Compiling the Processor System
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2.4. External Interface Custom Instructions
External interface custom instruction is an extension to the multicycle custom instructions. External interface custom instructions allow you to add an interface for communicating with logic that is not in the processor's datapath. You can generate conduits based on the available interconnects. Refer to the Intel® Quartus® Prime Pro Edition User Guide: Platform Designer - Platform Designer Interconnect.
At system generation, you can export an interface in the Platform Designer by double clicking on the interface to export it allowing external logic to 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 8. 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 provides a dedicated path for data to flow into or out of the Nios® V processor. For example, custom instruction logic with an external interface can feed data directly from the Nios® V processor’s register file to an external first-in first-out (FIFO) memory buffer.