This is a DRAM test code, which I used to test my video card chips in that video: https://www.youtube.com/watch?v=MZvCcadwblg&t=330s
Arduino seems to be too slow to keep up with required RAS-to-CAS delay. I got it as fast as I could so far and it seems to be sufficient to make some simple read/write tests. However, I couldn't get managed to write a complete run through tests, writing/reading patterns and validating all address space. The program seem to run for some time, but suddenly stops working after a while. The patterns do not match, despite, that I know, that the chip is ok. I tested it on many chips with different timings, but unfortunately all with the same result. I guess, it's due to some timing issues and because Arduino is just not able to keep up with required delays. Anyway, this code is sufficient to make some random tests, this doesn't tell if the whole DRAM address space is good, but at least it is sufficient to tell if the memory chips are working at all.