Example(s) for using an external DDR memory

[umarcor]

Coming from #98.

#98 (comment)

The OrangeCrab has an external DDR with 128 MB. Hence, the mid-term goal should be to append a controller to the external bus of the NEORV32 and have the IMEM and/or DMEM assigned there.

Note that we can have mixed-language designs. Therefore, we might use the same strategy as in antonblanchard/microwatt: they use litedram (see enjoy-digital/litedram).

#98 (comment)

That looks very good! I'm very happy that the memory controller supports Wishbone so there is no need for extra bridging logic.
I will check out the documentation. That would be also a nice add-on for the current Quartus and Vivado examples.

[jeremyherbert]

I am happy to help test this when the time comes.

[stnolting]

We now have two links to projects that have SDRAM support in setups:

• https://github.com/emb4fun/neorv32-examples (Intel) by @emb4fun
• https://github.com/zipotron/neorv32-complex-setups (Lattice, work-in-progress) by @zipotron

So I think this can be closed?! The litedram/litex approach mentioned by @umarcor should be further discuseed in #115.

[umarcor]

@stnolting, agree.