This is a WIP modified version of the Wishbone SD card controller intended for smaller FPGAs with less resources. It makes the following changes:

• Replaced Wishbone bus with an 8-bit interface, with an 8-bit address and 8-bit data in/out per transfer
• Heavily optimized RTL, resulting in a ~60% reduction in LUTs (~850 LUTs and 480 FF on a Lattice ICE40)

Wishbone SD Card Controller IP Core

The Wishbone SD Card Controller IP Core is MMC/SD communication controller designed to be used in a System-on-Chip. IP core provides simple interface for any CPU with Wishbone bus. The communication between the MMC/SD card controller and MMC/SD card is performed according to the MMC/SD protocol.

Introduction

This core is based on the "sd card controller" project from http://opencores.org/project,sdcard_mass_storage_controller but has been largely rewritten. A lot of effort has been made to make the core more generic and easily usable with OSs like Linux.

• data transfer commands are not fixed
• data transfer block size is configurable
• multiple block transfer support
• R2 responses (136 bit) support

Features

The MMC/SD card controller provides following features:

• 1- or 4-bit MMC/SD mode (does not support SPI mode),
• 32-bit Wishbone interface,
• DMA engine for data transfers,
• Interrupt generation on completion of data and command transactions,
• Configurable data transfer block size,
• Support for any command code (including multiple data block tranfser),
• Support for R1, R1b, R2(136-bit), R3, R6 and R7 responses.

Documentation

The documentation is located in the doc/ directory.

Examples

A sample ORPSoC project that make use of this core is located at:

https://github.com/mczerski/orpsoc-de0_nano

The project is based on de0_nano board with custom made expansion board with SD Card connector.

There is also u-boot project port for this board located at:

https://github.com/mczerski/u-boot

This u-boot project contains driver for Wishbone SD Card Controller IP Core and can be configured for de0_nano board (with custom made expansion board).

Also in the plan is the driver for Linux. The initial work can be found at:

https://github.com/mczerski/linux - de0_nano branch

the driver is named ocsdc and is located in drivers/mmc/host directory.

TODO:

• rx/tx fifo treshold to do block transfers rather than many signle word transfers
• maybe one fifo rathen than two fifos (rx and tx) would suffice since the transfer between card and controller is always half-duplex
• read only and card detect signals support