Support the SPI RAM found on HAD badge

[mithro]

The HackADay badge has

two Lyontek LY68L6400 64 Mbit SPI SRAM chips

These SPI SRAM chips, kinda look like SPI NOR chips.

It would be good to have these devices supported as memory mappable for both read and write.

Clock rate:

• 33MHz(max) for normal read
• 100MHz(max) for fast read
• Mode: SPI/QPI

Datasheet -> https://www.electrodragon.com/w/images/0/04/LY68L6400_0.3.pdf

[machdyne]

Hi @mithro. I have been trying to get memory-mapped (Q)SPI PSRAM working with LiteX for some time now with no success. I have some working Verilog for QSPI PSRAM in this repo: https://github.com/machdyne/qqspi

If anyone wants to attempt this I can probably provide a 32MB QSPI PSRAM PMOD.

[xobs]

I had this working in https://github.com/xobs/haddecks/blob/master/rtl/spi_ram.py, and I was working on interleaving access in https://github.com/xobs/haddecks/blob/master/rtl/spi_ram_dual.py

There are tests in https://github.com/xobs/haddecks/blob/master/sim/spiram.v

[machdyne]

Thanks! This is working for me. I had to use dummy=6 with APS6404L-3SQR-SN PSRAM.

Maybe this can be merged into litex.soc.cores or litespi?

I have noticed a few boards with similar SPI PSRAM and with the QQSPI PMOD it's possible to add 32MB to any board with a PMOD socket, having this capability in LiteX might be useful, especially for the smaller boards.

[suarezvictor]

I sucessfully integrated the PSRAM core from @xobs into a newer version of LiteX by patching the example SoC script, see https://github.com/litex-hub/micropython/commit/d7d2203cab9c2909395bbb5a9cff3d5016fa81a3

I think this is ready to go mainstream. Excellent core! It worked first time

[suarezvictor]

This development makes the PSRAM appear as SPI flash https://github.com/litex-hub/litex-boards/pull/476/commits/b1df2c0f85fbcd5d4880ae71c05ac39b0abc4291