Connecting an SD/MMC card to your BR-6104K router
-------------------------------------------------

    .. image:: sd_card.jpg

SD Card Slot
============

You will need to get hold of an SD card slot.  You can either just
buy one, or make one from an old floppy drive cable with edge connector
as I did.  Here's the connector:

  .. image:: floppy_connector_before.jpg

There's a polarising tab in the way on the right, so we're going to 
put the SD card to the left side of the connector instead.  We are 
going to use the SD card only in MMC mode, so we only need 7 wires.
Turn the connector over, so the cable is coming out of the top, and
carefully cut away all but 13 of the wires, as shown here:

  .. image:: floppy_connector.jpg

Notice I've left a short length of ribbon to make cable annotation 
a little easer, so from the left::

  CS (chip select)  dot-dash-dot
  MMC DI (data in)  dash-dot-dash-dot
  GND               solid black
  3.3v              solid red
  CLK               dots
  GND               solid black
  MMC DO (data out) dot-dash-dot-dash

NB:  When we talk about data in and data out it's with respect to the card.
This guide always gives these directions relative to the card, not the 
SPI interface on the board - be warned.


Board Connections
=================

You'll need to get out your solder sucker and iron and remove four 
LEDs: D9, D10, D11 and D12, bottom-right on the board.  You can 
link the bottom of the current-limiting resistor R85 to 
D12 anode, which you should be able to make out below.  I use this
trick to get 3.3v to a through-hole solder point, but of course you
could get 3.3v instead from any number of other places on the board.
C99 and C100 provide a close-by earthing point, again plenty of 
other places to find that.

  .. image:: board_wiring.jpg

Here is the connected SD card reader.  I was a bit sloppy about cable
lengths - it's probably better to make the wires as short as possible.

  .. image:: total.jpg

When inserting the card, ensure it is hard up against the left end of the 
connector, and that the SD card contacts meet the edge connector contacts.
The picture below shows the SD card pushed half-way in to indicate position
of the contacts.

  .. image:: floppy_connector2.jpg

OpenWrt Configuration
=====================

You will need to ensure you've selected the mmc_over_gpio package:

  .. image:: config_mmc_gpio.jpg

You will also want to access files on the MMC card, so you could include
msdos/vfat.  Make sure you have cp437 (United stated codepage) module, or
you probably won't be able to mount the filesystem.

  .. image:: config_fs.jpg


Pin Configuration
=================

I almost forgot... we need to tell OpenWrt which pins we'll be using
for the MMC interface.  Edit the init file for the mmc_over_gpio 
package::

  vim package/mmc_over_gpio/files/mmc_over_gpio.init

The script is fairly easy to follow, and just seems to echo some 
numbers into one of the /sys files.  In this example I've already
changed the file to be compatible with the pins I've used above::

  #!/bin/sh /etc/rc.common
  # Copyright (C) 2008 OpenWrt.org
  START=90

  SYSFS="/sys"
  SYSFS_DRIVERDIR="$SYSFS/bus/platform/drivers/spi-gpio-mmc"

  # add_device(name, DI_pin, DO_pin, CLK_pin, CS_pin, mode)
  add_device() {
          echo -n "$1" "$2","$3","$4","$5" "$6" > $SYSFS_DRIVERDIR/add
  }

  # remove_device(name)
  remove_device() {
          echo -n "$1" > $SYSFS_DRIVERDIR/remove
  }

  start() {
          #FIXME we should use a config file, but I dunno how that parser
          #works.
          add_device "default" 21 17 20 18 0
  }

  stop() {
          remove_device "default"
  } 

You probably guessed the crucial line is::

  add_device "default" 21 17 20 18 0

Save the file with either these values, or alternatives if
you wired your card to the board differently to mine.  My init file
is available for download `here <mmc_over_gpio.init>`_.


First Boot
==========

The card should be recognised on boot, and if all works you should
get something like::

  mmc_spi spi32766.0: ASSUMING 3.2-3.4 V slot power
  mmc_spi spi32766.0: SD/MMC host mmc0, no DMA, no WP, no poweroff
  spi-gpio-mmc: MMC-Card "default" attached to GPIO pins 21,17,20,18
  mmc_spi spi32766.0: can't change chip-select polarity
  mmc0: problem reading switch capabilities, performance might suffer.
  mmc0: new SD card on SPI
  mmcblk0: mmc0:0000       979456KiB
   mmcblk0:

If you get::

  mmc0: error -22 whilst initialising SDIO card

then go back and check your wiring and/or the position of the SD card in
the edge connector.

To use the card you can format and mount /dev/mmcblk0, or alternatively 
one of the partitions (e.g. /dev/mmcblk0p1), depending on how you've 
set it up.