HSMC interface IO in SOPC Builder

So what you need is a component that does the serial-to-parallel conversion and present the data in a way that can be understood by the Nios CPU. I don't think that such a component already exists (but I could be wrong), so you'll probably have to create your own custom component.

I would recommend that this custom component presents the parallel data using the Avalon Stream protocol. It is very easy to implement, and you'll be able to use SOPC builder ready available components to handle the actual transfer to memory (a double clocked fifo and a sgdma, as an example).