FlashFilesystemsMTD < DULG

%SECTION0{name=FlashFilesystemsMtd}% Memory Technology Devices

All currently available flash filesystems are based on the Memory
Technology Devices *MTD* layer, so you must enable (at least) the
following configuration options to get flash filesystem support in
your system:

<pre>
CONFIG_MTD=y
CONFIG_MTD_PARTITIONS=y
CONFIG_MTD_CHAR=y
CONFIG_MTD_BLOCK=y
CONFIG_MTD_CFI=y
CONFIG_MTD_GEN_PROBE=y
CONFIG_MTD_CFI_AMDSTD=y
CONFIG_MTD_ROM=y
CONFIG_MTD_%BOARD%=y
</pre>

%X% Note: this configuration uses *CFI* conformant AMD flash chips;
you may need to adjust these settings on other boards.

%IF{ "%HAVE_FDT%" eq "true" }%
The partition layout of the flash devices is contained in the flat
device tree for the system (see %REF{type=Section,topic=Appendix,name=FlatDeviceTree}%).
%ELSE%
The layout of your flash devices ("partitioning") in 2.4 Linux kernels
was defined by the mapping routines for your board in the Linux MTD sources
(see _drivers/mtd/maps/_).

The configuration for the %BOARDNAME%
looks like this:

%INCLUDE{DULGData_%BOARD%.LinuxMtdMap}%

<!-- now we need a matching explanation, so please provide one! -->
%INCLUDE{DULGData_%BOARD%.LinuxMtdLayout}%
%ENDIF%

Informational messages of the =MTD= subsystem can be found in the
Linux bootlog, i.e. see section %REF{type=Section,topic=LinuxNfsRoot,name=LinuxBootlog}%.

One can discover this information in a running system
using the =proc= filesystem:

%INCLUDE{DULGData_%BOARD%.LinuxProcMtd}%

Now we can run some basic tests to verify that the flash driver
routines and the partitioning works as expected:

%INCLUDE{DULGData_%BOARD%.LinuxMtdDump}%

In the hex-dumps of the MTD devices you can identify some strings
that verify that we indeed see an U-Boot environment,
a Linux kernel, a ramdisk image and an empty partition to play wih.

The last output shows the partition to be empty. We can try
write some data into it:

%INCLUDE{DULGData_%BOARD%.LinuxMtdWrite}%

As you can see it worked the first time.  When we tried to write 
the (new date) again, we got an error.
The reason is that the date has changed (probably at least the
seconds) and flash memory cannot be simply overwritten - it has to be
erased first.

You can use the =eraseall= Linux commands to erase a whole MTD
partition:

%INCLUDE{DULGData_%BOARD%.LinuxMtdErase}%

We have now sufficient  proof  that  the  MTD  layer  is  working  as
expected,  so we can try creating a flash filesystem.
9.1. Flash Filesystems		1. Abstract		9.1.2. Journalling Flash File System
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