This repository contains two Verilog hardware RTL controllers for handling SD cards from an FPGA. The first and older controller handles SD cards via their (optional) SPI interface. The second and newer controller works using the SDIO interface. This second controller has also been demonstrated to handle eMMC cards as well.
The SDSPI controller exports an SD card controller interface from internal to an FPGA to the rest of the FPGA core, while taking care of the lower level details internal to the interface. Unlike the SDIO controller in this respository, this controller focuses on the SPI interface of the SD Card. While this is a slower interface, the SPI interface is necessary to access the card when using a XuLA2 board (for which it was originally written), or in general any time the full 9--bit, bi--directional interface to the SD card has not been implemented. Further, for those who are die--hard Verilog authors, this core is written in Verilog as opposed to the XESS provided demonstration SD Card controller found on GitHub, which was written in VHDL. For those who are not such die--hard Verilog authors, this controller provides a lower level interface to the card than these other controllers. Whereas the XESS controller will automatically start up the card and interact with it, this controller requires external software to be used when interacting with the card. This makes this SDSPI controller both more versatile, in the face of potential changes to the card interface, but also less turn-key.
While this core was written for the purpose of being used with the ZipCPU, as enhanced by the Wishbone DMA controller used by the ZipCPU, nothing in this core prevents it from being used with any other architecture that supports the 32-bit Wishbone interface of this core.
This core has been written as a wishbone slave, not a master. Using the core together with a separate master, such as a CPU or a DMA controller, only makes sense. This design choice, however, also restricts the core from being able to use the multiple block write or multiple block read commands, restricting it to single block read and write commands alone.
Status: The SDSPI IP is silicon proven. It is no longer under active development. It has been used successfully in several FPGA projects. The components of this IP have formal proofs, which they are known to pass. A Verilator C++ model also exists which can fairly faithfully represent an SD card's SPI interface. A software library also exists which can act as a back end when using the FATFS library.
For more information, please consult the SDSPI user guide.
This repository also contains a second and newer SD card controller, designed to exploit both the full SDIO protocol and the 8b EMMC protocol--either with or without data strobes. This controller has been tested against both SDIO and eMMC chips, with the differences between the two types of chips handled by software.
The interface to this controller is roughly the same as that of the SDSPI controller, although there are enough significant differences to warrant a separate user guide.
The controller is designed to support IO modes all the way up to the HS400 mode used by eMMC. HS400 is an eMMC DDR mode based off of a 200MHz IO clock, using a data strobe pin on return. Also supported are an SDR mode using a 200MHz clock, DDR and SDR modes using a 100MHz clock, as well as both DDR and SDR support for integer divisions of the 100MHz clock, starting with a 50MHz clock and going all the way down to 100kHz. This is all based upon a nominal 100MHz system clock, together with a 400MHz clock for SERDES support. For designs without 8:1 and 1:8 SERDES IO components, 100MHz and slower clocks are still supported, depending upon whether or not DDR I/O components are available. Both open-drain and push-pull IOs are supported, and the front end can switch between the two as necessary based upon options within a PHY configuration register. No support is planned for any of the UHS-II protocols.
Both Wishbone and AXI-Lite interfaces are supported.
Status: The SDIO controller has now been silicon proven. It is currently working successfully in its first FPGA project, where it is being used to control both an SD card as well as an eMMC chip. Many of the components of this IP have formal proofs, which they are known to pass.
Notably missing among the component proofs is a proof of the front end. The front end's verification depends upon integrated simulation testing.
Both Verilog and C++ models have been built which can be used to test this controller in simulation, although only the Verilog SDIO and eMMC models have been tested to date.
For more information, please consult the SDIO user guide.
Although the initial RTL has both been fully drafted and successfully hardware tested, this project is far from finished. Several key steps remain before this controller will be a completed product:
-
Multi-block: Multiple block commands have been demonstrated in simulation for the SDIO model. While eMMC multiblock support exists, it hasn't yet been tested, and will likely fail.
Multiblock commands form the basis for the DMA's operation.
-
OPT_DMA: An optional DMA is now available, and passing tests in silicon.
Only the Wishbone version of the DMA controller exists at present. Although some components exist in my wb2axip repository which could support an AXI DMA, these components have neither been integrated nor tested as part of this design.
Since the eMMC model doesn't yet support the multi-block commands required by the DMA, DMA simulation testing has been limited to the SDIO model.
-
STREAM DMA: At customer request, hooks now exist for an (optional) stream DMA interface. This interface will accept an AXI stream input, and/or an AXI stream output. Data present on the AXI stream input may then be written directly to the device. Reads from the device may also produce data at the output stream. At present, the stream inputs must be a minimum of 32bits, and a power of two in width. The stream outputs must either be 32bits or the full bus width. No provision exist for stream data less than a word in size.
This interface will need to be tested together with the pending hardware tests for the DMA.
-
C++ Model: An early Verilator C++ model of an SDIO component has been drafted. It needs to be finished and tested. No C++ eMMC model exists at present, nor is any data strobe support is planned.
-
SW Testing: Control software has been written, and has been used to demonstrate both SDIO and EMMC performance. This software is designed to work with the FATFS library.
An integrated test bench exists for testing this software from a ZipCPU, it just hasn't (yet) been tested. Because this integrated test bench will require integration with an external project (i.e. the ZipCPU, further work is on hold pending a decision on how to integrate multiple dissimilar design components together for this purpose.
-
AXI Support: A version exists in the dev branch that supports an AXI-Lite interface.
-
eMMC Boot mode: No plan exists to support eMMC boot mode (at present). This decision will likely be revisited in the future.
Boot mode may require support for eMMC CRC tokens, which aren't (yet) supported. These are 8'bit return values, indicating whether or not a page has been read or written and passes its CRC check.
Some (untested) support exists for boot mode in the eMMC model.
Current logic usage is being tracked for iCE40 and Xilinx 6-LUT devices in the usage.txt file in the RTL/ directory.
Should you find the GPLv3 license insufficient for your needs, other licenses may be purchased from Gisselquist Technology, LLC.