Ethernet with DSP Dev. Kit Cyclone III (no NIOS)

By NIOS memory I meant any memory that can be accessed by the Nios CPU. So you should be able to read the DDR SDRAM too.

For the SDRAM access, it really depends on how you do it. If you put the DDR controller in the SOPC system, your custom IP and the NIOS can share access to the RAM. Arbitration will be made automatically by SOPC builder. Your custom IP will need to use an Avalon master interface to wlite to the RAM.

Another alternative could be to use a ready made DMA IP to write the data to RAM for you. If you format your data in Avalon streams, you can use the SGDMA IP to transfer it to RAM.