Why MTD ???

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Hi All

I am new to Flash File system. I am going through JFFS and YAFFS
material from internet.

I am not clear about Memory Technology Device layer...

.... How I can use this layer/subsystem when Implementing JFFS/YAFFS
file system.
what is the Necessity of this MTD.. Whether it will do any specific
function??

Plz clear me.. it will be a great help for me for my futher work.

Thanks

Gururaja B O


Re: Why MTD ???
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MTD is the driver layer needed for accessing the raw flash devices.
JFFS/YAFFS et al are filesystems, i.e. they are concerned about the
structuring of the data on the flash device, but they do not know
how do physically read/write to/from a flash device. The situation
is similar as with disk filesystems such as ext3/isofs/vfat/.. vs.
disk drivers sich as ide/scsi/floppy/...

HTH

Rob

--
Robert Kaiser                     email: rkaiser AT sysgo DOT com
SYSGO AG                          http://www.elinos.com
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Re: Why MTD ???
HI,

Below statement I got from
http://www.linux-mtd.infradead.org/archive/index.html site.

it tells about MTD that..

"The aim of the system is to make it simple to provide a driver for new
hardware, by providing a
generic interface between the hardware drivers and the upper layers of
the system"

What is the meaning of this? and How to integrate driver with MTD.?

Thanks


Re: Why MTD ???
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The "upper layers" mentioned would be the view of, for example, a
flash filesystem such as JFFS/YAFFS: To access the flash device
hardware, these filesystems need some knowledge about the device such
as what technology it is (e.g. NAND/NOR flash), how it is organized
(e.g. number and size of blocks), etc. Also, it needs some basic methods
that it can invoke to read or write from/to the flash and to erase
a block. This is the "generic interface" that the MTD layer provides.

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The answer, as usual, is: it depends...

The practical approach is to look at the MTD system, see what is
already there and see if any of it can be adapted/extended to support
your device. If the flash device you want integrated is similar
to the devices that are already supported (chances are that it is),
then integrating it can be as easy as configuring the right parameters.
In some cases, writing a mapping driver may suffice (this is also quite
simple, just look at the examples). Failing both you may need to get
really involved with the code or to hire a guru..

My suggestion for you is to ask the MTD mailing list wether MTD
has support for your device (give exact specifications). In my
experience, the people on the list are quite friendly and willing to
help.


HTH

Rob

--
Robert Kaiser                     email: rkaiser AT sysgo DOT com
SYSGO AG                          http://www.elinos.com
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Re: Why MTD ???
Hi

If i am porting YAFFS to other operating system[except LINUX] then
Whether MTD is needed? Because MTD is for Linux Operating System.

Thanks


Re: Why MTD ???
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The way I see it, You have two options:

1. Try to determine the MTD API subset that YAFFS uses and implement
   that from scratch on your platform, possibly ripping(*) code from
   MTD where appropriate.

2. leave YAFFS as it is and port the MTD system to your OS

Which of these is the way to go is impossible to decide at the
level of detail we are talking here. It would depend on how different
your target OS is from Linux and how generic you need the solution
to be (i.e. if you only need to deal with a single target hardware
configuration with just one, well-defined flash chip setup, then all the
genericism that MTD offers may not be worth the trouble involved in
porting it.).

I'm afraid this is the point where you will need to get your hands
dirty ...


HTH

Rob

(*) Keep in mind that you are dealing with GPLed code!

--
Robert Kaiser                     email: rkaiser AT sysgo DOT com
SYSGO AG                          http://www.elinos.com
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Re: Why MTD ???
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It depends on whether you'll make calls to MTD entries
from the ported code or if you're going to use some
other method to call the physical device drivers.

Your system has to have some way of controlling the
physical memory chips from the file system layer.

Please pay attention to the GNU Program License if you're
porting to a non-GPL operating system.

--

Tauno Voipio
tauno voipio (at) iki fi


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