sdspi VS openarty

I have built a lot of open-source C++ tooling for design verification. You can find a lot of my C++ models posted on my Github. Example C++ models include: UART, SPI/DSPI/QSPI Flash, SD-Card (SPI-based interface), VGA Video, Ethernet MDIO, PS/2 mouse, OLED display, SDRAM and more. (I've even simulated PLLs using C++ models ...) I have also written extensively about doing so at ZipCPU.com.

You mean ... sort of like I did in this project? I implemented an SPI based controller, where the controller took care of all the bit-banging for you, but the CPU still needed to issue the commands as appropriate for the protocol?

How about an SD card controller? I know I have a SPI based SD card controller, but the SDIO isn't that much harder. If you look hard enough you can find open source SDIO controllers.

There are also open source versions of many of the pieces you will need. I now use an open source crossbar interconnect for most of my designs. I use AutoFPGA to connect all the pieces together. I mentioned my flash controller above, but I also have a SD Card controller I've used quite successfully. I've also posted a UART to Wishbone bridge and discussed network debugging, both of which I use routinely with the ZipCPU. If for no other reason, these components allow me to load or update software on my CPU even after it's been placed into an FPGA. Of course, many of those components are tied to a Wishbone bus infrastructure. You may find you need a bridge of some type to connect different buses structures together--memory naturally tends to operate at one width and clock, video at another, and your CPU at another, so it helps at times to have a universal bus adapter kit handy.

I have built a lot of open-source C++ tooling for design verification. You can find a lot of my C++ models posted on my Github. Example C++ models include: UART, SPI/DSPI/QSPI Flash, SD-Card (SPI-based interface), VGA Video, Ethernet MDIO, PS/2 mouse, OLED display, SDRAM and more. (I've even simulated PLLs using C++ models ...) I have also written extensively about doing so at ZipCPU.com.

The repo is the example design. It was used by software, though, that's not (currently) posted. A lot of math went into the coefficients as well--that's all in the software.

Here's the flash controller repo I use. There's a flash controller in there for SPI, Dual SPI, and Quad SPI. The Dual and Quad SPI controllers need a device specific startup script to get them into the right mode. This script should be fairly well explained by the comments. You should find at least one of these controllers that works for you. More recent versions of the controller have a Wishbone arbiter within them -- they're just not checked in the repo yet. (DSPI, QSPI). This makes it so the design fully supports two two Wishbone ports: a config port by which you can send any value and the memory mapped read port. (You can't use both at the same time.)

You can compare my configuration file for the Spansion flash with my config file for the Micron flash to see that these are the only two hardware differences between the two

I'd then recommend Verilator for simulation testing--but only after your formal design checking is complete. You can find online C++ models of a QSPI flash, RAM, and a serial port which should be good enough to get you going here. When you are ready for more permanent storage, there's also a decent C++ model of an SD card (SPI only).