PmodSD in Microblaze and integrating SoC with IPs

[JColvin]

A customer on our website asked a couple of questions:

Hi, it's me again. I need to use the pmod SD with the microblaze soft processor, however I see no good tutorial for this. I am using Vivado and am only proficient with VHDL. Please help.

and

Hi. One more thing. can you direct me to a tutorial on how to integrate the part of the Soc that I have written in VHDL with the IPs provided by Vivado. Thanks for your time.

The response is below.

[JColvin]

Hello,

I have asked some of our applications engineers for feedback on both of your questions. In regards to your second question though, it will be helpful for our applications engineers to know what SoC you have written and which IPs you are referring to.

Thanks,
JColvin

[D@n]

Hello, and welcome to the forum!

First, though, I'm not one of the applications engineers JColvin has asked for feedback.  Still, I've built FPGA interfaces to SDCards before, and I'm currently building a SPI interface to an SD card (currently an empty link--I'll fix that soon) as part of a SoC for the XuLA2-LX25 board by xess.com.  Incidentally, this is a SoC that I have written, so I know what you are up to.  It's also a SoC built around the ZipCPU, something else that I have written--to include the GCC toolchain that comes with it.

I have integrated all of my components with the various SoC's that I have written using a non-proprietary, open standard Wishbone bus.  It hasn't been that hard to use.  You can also find an SD card controller that works off of the Wishbone bus here on OpenCores.  If you aren't familiar with the wishbone bus, I would commend it to your attention.

If you aren't interested in the wishbone bus, or perhaps aren't so interested in Verilog sources, being a VHDL type yourself, you can still find an SD Card controller using the SPI interface, written in VHDL, here.  (It's part of the software package for the XuLA board as well ...)  Don't let this XuLA stuff scare you, by the way, the FPGA interaction with an SD-Card is always over the same wires: CMD, DATA0-3, and CLK for the parallel SD interface, and CS, CLK, MISO, and MOSI for the SPI interface.  These are the same wires you'll get from the PModSD--giving you a choice of which interface you wish to use.  (Both SD and SPI protocols for communicating with an SD card use the same wires, they just use them ... differently.  Be aware, the DATA0-3 and CMD lines in SD mode are bi-directional, so there is an extra bit of complexity should you wish to use that piece.  The complexity will buy you a faster interface, though.)

If, however, what you are interested in is connecting to the IP core referenced in Vivado, then you may need to look here for the specification of the LogicBricks SD host card controller, although I'll admit ... that piece of documentation appears to be too light to do anything with.  Perhaps you can find some more details somewhere.  I would expect that interface to connect to an AXI bus, but beyond that I don't personally have much information.

Yours,

Dan