Arria 10 access all DDR4 memory chips for test with NIOS II

The board I am designing has 9 8Gb DDR4 memory chips, for a total of 72 DQ lines (8 per chip). I want to verify that all chips are present and working by reading and writing to an address on each chip, using the NIOS II Core via EMIF.

The way I see it at present, using the Address Span Extender, I can only access concurrent blocks of memory, which would mean using up a massive amount of NIOS memory addresses which I don't need to use.

Is there any way to map the NIOS to the DDR4 such that I can smaller spaced out address windows? I thought the offset would be an offset between windows, but infact just offsets the base address. If more than 2 windows are set, this option is even disabled from changing.

Is there a suitable way to implement such a test with the NIOS and DDR4? Perhaps there is some way I can use DMA to test all the RAM, store results in a register and check that with the NIOS? I'm not sure how I'd implement something like this - I am new to FPGA.

Any and all suggestions are appreciated, thanks.