Minimalistic SDHC Host Reader (SPI mode)

Minimalistic SDHC HOST reader is an SD host controller useful for bootloaders operations. It implements the SD card protocol in a Finite States Machine written in VHDL. No additional microcontroller/software is required to read data from the SD card. This module can be used as a peripheral for some microcontroller or used alone to read raw data from an SD card.

Additional documentation can be found at doc directory in minsdhcspi-host.pdf document. Also, the examples directory contains demos for some prototype boards based in Xilinx FPGAs devices.

Features and limitations

Only SDHC cards are supported
Four SPI speeds are supported: 25MHz, 12MHz, 780KHz and 97KHz
A Picoblaze-3 interface is available

Download

git clone https://github.com/paulino/minsdhcspi-host

The examples require an external repository with a set of peripherals for Digilent Inc. Boards, be sure you clone the repository including all submodules with the command

git clone --recursive https://github.com/paulino/minsdhcspi-host

Demos

The examples directory contains some projects for Xilinx ISE and Vivado and them have been tested in Spartan3 and Virtex7 FPGAs. The tests run at Digilent Inc. prototype boards.

See examples/README.md for more info.

About SPI speed

SD card initialization runs at ~80KHz, after the initialization success SPI speed changes to a pre-programmed speed in the source code. This part is not finished in this version and the read speed is set to 12MHz by default. Anyway it can be changed at file rtl/sdcmd.vhdl in the state ST_INIT_1 about line 181:

spi_data_in(3 downto 0) <= "0010";  -- set SPI clock speed to CLK/4 = 12MHz

Valid values are:

Value	Div	Frec.
1000	clk/2	25MHz
0100	clk/4	12MHz
0010	clk/64	780KHz
0001	clk/512	97KHz

This will be improved in future versions.

Picoblaze interface

This core can be added easely to Picoblaze microcontroller as a peripheral. The file rtl/if_picoblaze.vhdl has glue logic for Picoblaze.

Detailed info about this is at doc directory.

Simulation alternative architecture

At directory bench there is a simulation architecture for the top module in the file sdspihost_sim.vhd.

To use this architecture the SD card raw data must be converted to a 16 columns text file format. A script to do it is suplied in scripts directory and the next commands show how to use it

$ dd if=/dev/sdX of=sdcard.raw bs=1024 count=200
$ ./raw2int.py sdcard.raw > sdcard.txt

The script raw2int.py converts binary data to a integer sequence of numbers in text mode. It is necessary to use it due detected problems while reading binary files directly from VHDL code with ISIM.

The file sdcard.txt is used in SDHOST simulation architecture as data source. Be carefully with size of this file!

Authors

This module is published and maintained by Paulino Ruiz-de-Clavijo Vázquez <paulino@dte.us.es>, Departamento de Tecnología Electrónica, Universidad de Sevilla.

If you use the module we are grateful, and you can use the following biblatex entries to cite us:

# BibLaTex entries
@online{minsdhcspi-host,
  title={{Minimalistic SDHC HOST reader}},
  author={Paulino Ruiz-de-Clavijo},
  organization={{Dpto. Tecnología Electrónica, Universidad de Sevilla}},
  year={2017},
  url={https://github.com/paulino/sdspihost},
  urldate={2017-04-19}
}

@article{ruiz2017,
  title = "Minimalistic SDHC-SPI hardware reader module for boot loader applications ",
  journal = "Microelectronics Journal ",
  volume = "67",
  pages = "32 - 37",
  year = "2017",
  issn = "0026-2692",
  doi = "https://doi.org/10.1016/j.mejo.2017.07.007",
  url = "http://www.sciencedirect.com/science/article/pii/S0026269216305183",
  author = "Paulino Ruiz-de-Clavijo and Enrique Ostúa and Manuel-J. Bellido and Jorge Juan and Julián Viejo and David Guerrero",

}