Subversion Repositories spi_boot

README for the spi_boot core

============================

Version: $Id: README 77 2009-04-01 19:53:14Z arniml $

Description

-----------

The SD/MMC Bootloader is a CPLD design that manages configuration and

bootstrapping of FPGAs. It is able to retrieve the required data from

SecureDigital (SD) cards or MultiMediaCards (MMC) and manages the FPGA

configuration process. SD cards as well as MMCs are operated in SPI mode which

is part of both standards thus eliminating the need for dedicated

implementations. The SD/MMC Bootloader fits both. Beyond configuration, this

core supports a bootstrapping strategy where multiple images are stored on one

single memory card.

For example consider a system completely based on SRAM. The bootloader

provides the initial configuration data from the first image to the FPGA. This

image contains a design which pulls the next image from the memory card and

transfers this data to SRAM. In the third step the final FPGA design is loaded

from the third image.

These images are clustered in sets which can be selected by external switches

for example. Several configuration sets can be stored on one memory card

allowing you to provide a number of applications which are downloaded quickly

to the FPGA.

The schematic (rev. B) shows how the core can be used with an FPGA board. I

use it to configure/boot the Xilinx Spartan IIe on BurchED's B5-X300

board. SV2 fits the "SERIAL MODE" connector on this board but you will have to

add a separate wire from R6 to attach INIT. Please check the proper use of the

pull-up resistors for your specific board.

Features

--------

* Configuration mode: configures SRAM based FPGAs via slave serial mode

  (Xilinx and Altera)

* Data mode: provides stored data over a simple synchronous serial interface

* Broad compatability using SPI mode

    + SecureDigital cards using dedicated initialization command

    + MultiMediaCards (see below)

* Operation triggerd by power-up or card insertion

* Multiple configuration sets stored on on single memory card

Compatability

-------------

These cards have been tested with the SD/MMC Bootloader:

  * Hama 64 MB SD

  * SanDisk 128 MB SD

  * SanDisk 64 MB MMC

  * Panasonic 32 MB SD

Some MMC might fail with this core as not all cards support CMD18

(READ_MULTIPLE_BLOCK). Please consult the data sheet of your specific

model. In case your MMC does not implement CMD18 you might want to have a look

at the FPGA MMC-Card Config project.

Tools

-----

Downloading the configuration data to the card is a straight forward

process. The images have to be written starting at dedicated locations. For

the provided toplevel designs, these locations are multiples of 256 K. I.e. 0,

0x40000, 0x80000 and so forth.

dd (part of the GNU coreutils) serves this purpose:

$ dd if=ram_loader.bin of=/dev/sdX bs=512

$ dd if=pongrom_6.bin of=/dev/sdX bs=512 seek=512

$ dd if=pacman.bin of=/dev/sdX bs=512 seek=1024

The name of the device node depends on how the card reader is attached to the

kernel. For Linux systems this is most often something like /dev/sdX with X

ranging from a-z. Please note that it is essential to use the device without

any trailing numbers as they refer to partitions leading to wrong offsets for

data written to the card.

All this works perfectly for my Spartan IIe device as this FPGA expects the

configuration data as it is delivered from the card: Consecutive bytes each

with its most significant bit first. Altera devices like the FLEX family are

different here. They expect the bytes with least significant bit

first. Therefore, the configuration data has to be swapped bitwise before it

is written to the card. Michael Libeskind kindly provided a program that

accimplishes this task. Find it in sw/misc/bit_reverse.c.

Verification

------------

The spi_boot core comes with a simple testbench that simulates an SD/MMC

card. All four implementations of the core are verified there in parallel

while transferring the data for several sets.

You should normally not need to run the testbench. But in case you modified

the VHDL code the testbench gives some hints if the design has been broken.

Directory Structure

-------------------

The core's directory structure follows the proposal of OpenCores.org.

spi_boot

 |

 \--+-- doc                 : Documentation

    |    |

    |    \-- src            : Source files of documentation

    |

    +-- rtl

    |    |

    |    \-- vhdl           : VHDL code containing the RTL description

    |                         of the core.

    |

    +-- bench

    |    |

    |    \-- vhdl           : VHDL testbench code.

    |

    \-- sim

         |

         \-- rtl_sim        : Directory for running simulations.

RAM Loader

----------

Directory rtl/vhdl/ram_loader contains the sample design which loads the next

image from the card and stores its contents to external asynchronous

RAM. After reading 64 KB it triggers a new configuration process for the final

FPGA design.

Refer to the code for the mechanisms involved.

Compiling the VHDL Code

-----------------------

VHDL compilation and simulation tasks take place inside in sim/rtl_sim

directory. The project setup supports only the GHDL simulator (see

http://ghdl.free.fr).

To compile the code simply type at the shell

$ make

This should result in a file called tb_behav_c0 which can be executed as any

other executable.

The basic simple sequence list can be found in COMPILE_LIST. This can be

useful to quickly set up the analyze stage of any compiler or

synthesizer. Especially when synthesizing the code, you want to skip the VHDL

configurations in *-c.vhd and everything below the bench/ directory.

References

----------

  * SanDisk SD Card Product Manual

    http://www.sandisk.com/pdf/oem/ProdManualSDCardv1.9.pdf

  * SanDisk MMC Product Manual

    http://www.sandisk.com/pdf/oem/manual-rs-mmcv1.0.pdf

  * Toshiba SD Card Specification

    http://i.cmpnet.com/chipcenter/memory/images/prod055.pdf

  * BurchED

    http://burched.biz/

  * FPGA MMC-Card Config project

    http://www.opencores.org/projects.cgi/web/mmcfpgaconfig/overview