Cf Card vs DiskOnChip

Cf Card vs DiskOnChip

[Ramya Ravichandran]

Hi,

   I am a newbie  developing a embedded linux
controller for an industrial environment. I am unable
to decide whether to use a Compact Flash card or
DiskOnChip.With 128MB I need to get the whole thing
running.
Can someone plese tell me as which one to use and why?

Thanks
Ramya

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Re: Cf Card vs DiskOnChip

[David Woodhouse]

rrhsin@yahoo.co.in said:
> 
>    I am a newbie  developing a embedded linux controller for an
> industrial environment. I am unable to decide whether to use a Compact
> Flash card or DiskOnChip.With 128MB I need to get the whole thing
> running. Can someone plese tell me as which one to use and why? 

People have reported severe reliability problems with CF cards. With the 
DiskOnChip, all the translation stuff to emulate a block device is done in 
software, which is probably a better option.

The downside of the DiskOnChip is that the Linux driver doesn't do wear 
levelling, although it's easy enough to add, and that the vendor's driver 
is a binary-only module and hence of dubious legality.

I would go for the DiskOnChip and add wear levelling support - all you need 
to do it make it randomly pick a clean block for erasure occasionally, to 
make sure stuff moves around over time.


--
dwmw2

Re: Cf Card vs DiskOnChip

[Nikhil Goel]

David Woodhouse wrote:

> rrhsin@yahoo.co.in said:
> 
>>industrial environment. I am unable to decide whether to use a Compact
>>Flash card or DiskOnChip.With 128MB I need to get the whole thing
>>running. Can someone plese tell me as which one to use and why? 
> 
> The downside of the DiskOnChip is that the Linux driver doesn't do wear 
> levelling, although it's easy enough to add, and that the vendor's driver 
> is a binary-only module and hence of dubious legality.
> 
> I would go for the DiskOnChip and add wear levelling support - all you need 
> to do it make it randomly pick a clean block for erasure occasionally, to 
> make sure stuff moves around over time.


Isn't that similar to the implementation of JFFS? So a DiskOnChip 
running on the CVS based driver with JFFS should suffice for 
wear-levelling! if I am missing some piece here, what should I rtfm?

regards,
nikhil



-- 

-- 
Nikhil Goel <nikhil@smartbridges.com>
Ph: +65 3240210  Ext 20, Fax: +65 3240607
Reality is a crutch for those who can't handle science fiction.

Re: Cf Card vs DiskOnChip

[David Woodhouse]

nikhil@smartbridges.com said:
>  Isn't that similar to the implementation of JFFS? So a DiskOnChip
> running on the CVS based driver with JFFS should suffice for
> wear-levelling! if I am missing some piece here, what should I rtfm? 

You could use JFFS on the DiskOnChip. You can't use JFFS2 at the moment 
because it doesn't properly support NAND flash - there are a few extra 
constraints that JFFS2 doesn't meet. It's not too hard to fix though - 
various people have indicated an interest in working on it.

--
dwmw2

Re: Cf Card vs DiskOnChip

[Richard Gooch]

David Woodhouse writes:
> People have reported severe reliability problems with CF cards. With
> the DiskOnChip, all the translation stuff to emulate a block device
> is done in software, which is probably a better option.

What kind of reliability problems? Cards that are DOA? Or random bit
errors during usage?

				Regards,

					Richard....
Permanent: rgooch@atnf.csiro.au
Current:   rgooch@ras.ucalgary.ca

Re: Cf Card vs DiskOnChip

[David Woodhouse]

rgooch@ras.ucalgary.ca said:
>  What kind of reliability problems? Cards that are DOA? Or random bit
> errors during usage? 

Death on power failure.

Vipin's report at http://www.embeddedlinuxworks.com/articles/jffs_guide.html
seems fairly typical.

--
dwmw2

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> >  What kind of reliability problems? Cards that are
> DOA? Or random bit
> > errors during usage? 
> 
> Death on power failure.
> 
> Vipin's report at
>
http://www.embeddedlinuxworks.com/articles/jffs_guide.html
> seems fairly typical.

Thanks but price is a major concern for us and CF
cards are 1/3 rd the price of DOC.So I guess my PM
might settle for CF cards.

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Re: Cf Card vs DiskOnChip

[Russ Dill]

On Fri, 2002-01-25 at 21:19, Ramya Ravichandran wrote:
> > >  What kind of reliability problems? Cards that are
> > DOA? Or random bit
> > > errors during usage? 
> > 
> > Death on power failure.
> > 
> > Vipin's report at
> >
> http://www.embeddedlinuxworks.com/articles/jffs_guide.html
> > seems fairly typical.
> 
> Thanks but price is a major concern for us and CF
> cards are 1/3 rd the price of DOC.So I guess my PM
> might settle for CF cards.

did you miss the discussion on not needing 128M?

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> did you miss the discussion on not needing 128M?

Doesn't the ROM needed  depend on the application than
runs on Linux? 

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Re: Cf Card vs DiskOnChip

[kira brown]

On Fri, 25 Jan 2002, Ramya Ravichandran wrote:

> Thanks but price is a major concern for us

Who do you work for?  I want to make sure I never buy anything from you.

k.

Re: Cf Card vs DiskOnChip

[kira brown]

On Fri, 25 Jan 2002, Ramya Ravichandran wrote:

> Hi,
>
>    I am a newbie  developing a embedded linux
> controller for an industrial environment. I am unable
> to decide whether to use a Compact Flash card or
> DiskOnChip.With 128MB I need to get the whole thing
> running.

Why on earth do you need so much storage?

k.

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> > Hi,
> >
> >    I am a newbie  developing a embedded linux
> > controller for an industrial environment. I am
> unable
> > to decide whether to use a Compact Flash card or
> > DiskOnChip.With 128MB I need to get the whole
> thing
> > running.
> 
> Why on earth do you need so much storage?
> 
I need to have an application running on it with
serial communication



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Re: Cf Card vs DiskOnChip

[Robert Schwebel]

On Fri, 25 Jan 2002, Ramya Ravichandran wrote:
> > > With 128MB I need to get the whole thing running.
> >
> > Why on earth do you need so much storage?
> >
> I need to have an application running on it with
> serial communication

If you don't need anything else 2 MB flash are enough. Remember, this is
Linux, not <beeeeep!> :-)

Robert
--
 +--------------------------------------------------------+
 | Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de |
 | Pengutronix - Linux Solutions for Science and Industry |
 |   Braunschweiger Str. 79,  31134 Hildesheim, Germany   |
 |    Phone: +49-5121-28619-0 |  Fax: +49-5121-28619-4    |
 +--------------------------------------------------------+

RE: Cf Card vs DiskOnChip

[Chris Fowler]

You do not really need 128m.  You may be starting from the worng direction.

I've seen 2 approaches to embedded stuff..

First:

Start with an install of RedHAt 7.2 and strip it down!

Second:

Start with a empty directory and add to it.


99% of the time the First method will yield a huge image of stuff not
needed.  Including libraries.

If you are missing something in the second methiod then you'll know real
fast.  And add it.

I'm a little curious as to what people are doing with JFFS2.  I have 2
partions on my flash.  1 is ext2.  2nd is raw.  Raw is used to store
configs, data etc..
ext2 is used to store kernel, initrd and software image.  At boot initrd
reads the image and loads to a ramdisk.  Kernel mounts that ramdisk as root.
User never deals with the DOC2000 unless they flash and upgrade, save a
config, get ssh keys, or get serial number.  The sw image is an encrypted
ext2 disk image.

Questions:

Why do you need to mount your flash as r/w?
What else are you using the JFFS2 for?

If my box looses power then it comes back up no damage.  If you delete every
file, it comes back up now damage.

-----Original Message-----
From: linux-mtd-admin@lists.infradead.org
[mailto:linux-mtd-admin@lists.infradead.org]On Behalf Of Robert Schwebel
Sent: Friday, January 25, 2002 8:23 AM
To: linux-mtd@lists.infradead.org
Subject: Re: Cf Card vs DiskOnChip


On Fri, 25 Jan 2002, Ramya Ravichandran wrote:
> > > With 128MB I need to get the whole thing running.
> >
> > Why on earth do you need so much storage?
> >
> I need to have an application running on it with
> serial communication

If you don't need anything else 2 MB flash are enough. Remember, this is
Linux, not <beeeeep!> :-)

Robert
--
 +--------------------------------------------------------+
 | Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de |
 | Pengutronix - Linux Solutions for Science and Industry |
 |   Braunschweiger Str. 79,  31134 Hildesheim, Germany   |
 |    Phone: +49-5121-28619-0 |  Fax: +49-5121-28619-4    |
 +--------------------------------------------------------+


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Re: Cf Card vs DiskOnChip

[Johan Adolfsson]

 
> > > Hi,
> > >
> > >    I am a newbie  developing a embedded linux
> > > controller for an industrial environment. I am
> > unable
> > > to decide whether to use a Compact Flash card or
> > > DiskOnChip.With 128MB I need to get the whole
> > thing
> > > running.
> > 
> > Why on earth do you need so much storage?
> > 
> I need to have an application running on it with
> serial communication

I assume you need the storage for some large logs then?
To get a basic embedded Linux system doing serial communication
and networking 2MB flash should be enough.
/Johan

Re: Cf Card vs DiskOnChip

[kira brown]

On Fri, 25 Jan 2002, Johan Adolfsson wrote:

> I assume you need the storage for some large logs then?
> To get a basic embedded Linux system doing serial communication
> and networking 2MB flash should be enough.

Webview does five PLC protocols, ppp, http, ftp, telnet, ssh, full shell,
copy of bash and vi, *and* runs Java out of an 8Mbyte DiskOnChip and has
three megabytes of free space.  If you add the X and video stuff that
drops to 500k though.

kira.

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> > Doesn't the ROM needed  depend on the application
> than
> > runs on Linux? 
> > 
> 
> you said "serial application". Doesn't seem like
> much to me
> 

Right now I am trying to find out the price of DOC. I
tried the serach words "DiskOnChip" and "DiskOnChip
Price" . The search results explain DOC but don't give
the price.
   If the price of DOC  is less than the CF+IDE
adapter or CF + PCMCIA-CF adapter then I guess we will
settle for DOC.
   Also I dont know which adapter to go for PCMCIA or
IDE for CF as I am not a h/w person.
  


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Re: Cf Card vs DiskOnChip

[Charles Manning]

On Sat, 26 Jan 2002 19:29, Ramya Ravichandran wrote:
> > > Doesn't the ROM needed  depend on the application
> >
> > than
> >
> > > runs on Linux?
> >
> > you said "serial application". Doesn't seem like
> > much to me
>
> Right now I am trying to find out the price of DOC. I
> tried the serach words "DiskOnChip" and "DiskOnChip
> Price" . The search results explain DOC but don't give
> the price.
>    If the price of DOC  is less than the CF+IDE
> adapter or CF + PCMCIA-CF adapter then I guess we will
> settle for DOC.
>    Also I dont know which adapter to go for PCMCIA or
> IDE for CF as I am not a h/w person.
>

If the CF is "embedded" and you are not going to remove it while it is 
powered up (ie. use it like you would a DOC) then you quite likely do not 
need any PCMCIA adapter chips  I've seen a few designs using CF this way.

If you have an IDE bus/port on your board, then the following link also has 
an appnote on interfacing to that too.

See http://www.sandisk.com/tech/oem_design/cf_dc.asp for some app notes on 
doing this kinda thing.

NB Though... CF has no wear levelling and might give some product lifetime 
issues (it's really a consumer technology designed with a Kleenex mentality).

-- Charles

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> If the CF is "embedded" and you are not going to
> remove it while it is 
> powered up (ie. use it like you would a DOC) then
> you quite likely do not 
> need any PCMCIA adapter chips  I've seen a few
> designs using CF this way.
> 

You have a desktop system and in this desktop system I
just want to remove the HD and replace it with the CF
card or DOC .Do you need adapters for this. IF DOC
then can it be directly embedded in the motherboard.

Please help.


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Re: Cf Card vs DiskOnChip

[kira brown]

On Sat, 26 Jan 2002, Ramya Ravichandran wrote:

> You have a desktop system and in this desktop system I
> just want to remove the HD and replace it with the CF
> card or DOC

I thought you said you were building an industrial embedded system?

This doesn't sound like it's going to be embedded *or* industrial.

kira.

Re: Cf Card vs DiskOnChip

[Russ Dill]

On Sat, 2002-01-26 at 01:05, Ramya Ravichandran wrote:
> > If the CF is "embedded" and you are not going to
> > remove it while it is 
> > powered up (ie. use it like you would a DOC) then
> > you quite likely do not 
> > need any PCMCIA adapter chips  I've seen a few
> > designs using CF this way.
> > 
> 
> You have a desktop system and in this desktop system I
> just want to remove the HD and replace it with the CF
> card or DOC .Do you need adapters for this. IF DOC
> then can it be directly embedded in the motherboard.
> 

m-systems also has ISA card adapters for DOC's

Re: Cf Card vs DiskOnChip

[Charles Manning]

On Sat, 26 Jan 2002 21:05, Ramya Ravichandran wrote:
> > If the CF is "embedded" and you are not going to
> > remove it while it is
> > powered up (ie. use it like you would a DOC) then
> > you quite likely do not
> > need any PCMCIA adapter chips  I've seen a few
> > designs using CF this way.
>
> You have a desktop system and in this desktop system I
> just want to remove the HD and replace it with the CF
> card or DOC .Do you need adapters for this. IF DOC
> then can it be directly embedded in the motherboard.
>
> Please help.

OK so if I understand you correctly, you want to take a normal x86 system, 
throw away the hand disk and put int a CF instead.

If that is what you want to do then the sandisk link shows how.  All you need 
is a very simple cable that goes from a standard IDE connector to a CF socket.
My understanding, which might be off, is that if you look inside a Sandisk 
Flashdrive then that is what you'll find.

For all you nay-sayers, there are some good reasons to do this. One good 
reason to do this over a DOC-based solution is that you don't have to load 
special DOC access software or have a specail DOC-friendly BIOS. The system 
can't tell the difference between a CF and a rotating disk. It's a nice easy 
way to get from A toZ, especially for an exploratory product or an "embedded 
PC" that's going into a vehicle or other high vibration scenario that will 
shake a disk to death.

kira I reckon you're being a bit rude! An honest question deserves a useful 
answer - not abuse. Help or shut up. IMHO.

-- Charles

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> OK so if I understand you correctly, you want to
> take a normal x86 system, 
> throw away the hand disk and put int a CF instead.
> 
> If that is what you want to do then the sandisk link
> shows how.  All you need 
> is a very simple cable that goes from a standard IDE
> connector to a CF socket.
> My understanding, which might be off, is that if you
> look inside a Sandisk 
> Flashdrive then that is what you'll find.
> 
Thanks for all the help. I want to understand PCMCIA ,
IDE , connectors , adapters,BIOS, hot-swapping, CF
socket, wear levelling ... all these terms were used
by you guys when u were helping me but being a newbie
I don't understand these terms. Can anyone suggest
some resources for me to understand these things.


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Re: Cf Card vs DiskOnChip

[Charles Manning]

>
> Thanks for all the help. I want to understand PCMCIA ,
> IDE , connectors , adapters,BIOS, hot-swapping, CF
> socket, wear levelling ... all these terms were used
> by you guys when u were helping me but being a newbie
> I don't understand these terms. Can anyone suggest
> some resources for me to understand these things.
>

Most of these are outside the scope of this discussion list.... you might 
want to call on uncle Google. 

IDE (loosely) is the way most hard drives are hooked up. Most drives are "IDE 
drives".
Compact Flash is a sub-set of PCMCIA. CF (and ATA-style PCMCIA cards) just 
look like a PCMCIA version of an IDE drive. Because they are PCMCIA capable 
yo can use extra pins to find out details about what the card is. This is 
used so that when you plug the card the system can tell the difference 
between a flash card and a modem - or whatever - and use the correct driver.

When you hook up a Compact Flash to the IDE bus, then you are not using those 
extra pins. It just looks like a disk drive. Hint: don't try hook up a modem 
to the IDE bus!

Flash has a limited number of times it can be erased. Somewhere between 1000 
and 1000,000 is typical depending on the technology, temperature, voltage. 
This is termed the "endurance". Because a disk drive/file system tesnds to 
erase/write some areas more often than others (eg. your program files will 
very seldom be written but data files and temporary files will get written a 
lot) some parts of the flash will wear out faster than others. Thus, maybe 
one file area might wear out long before the device wears out. To stop this 
happening, (or at least reduce it), wear levelling algorithms are used to 
move stuff around and level out the wearing.  Some devices do not apply wear 
levelling (eg. Compact Flash and SmartMedia). Some do (eg. full-size PCMCIA 
cards, DOC, JFFS).

The rest of what you ask is definitely beyond the scope of this discussion - 
try Google for a start.

Maybe an MTD FAQ/glossary could be useful?


-- Charles

Re: Cf Card vs DiskOnChip

[kira brown]

On Mon, 28 Jan 2002, Charles Manning wrote:

> kira I reckon you're being a bit rude!

I'm sorry, I just don't have much respect for people who say things like
'cost is more important than reliability'.  Probably becasue I've cleaned
up their messes so often.

I also don't understand the point of fitting an unreliable Flash to
replace the hard disc in an ordinary PC.  It's not as if it will be any
faster (CF is much slower than a rotating IDE disc) or last any longer
(since CFs tend to drop dead unexpectedly).  Neither can you build a
system free of moving parts, since it will still need a cooling fan or
two.  The only thing you can say is that the power supply requirements
will be a bit smaller-  but if you were really worried about that, why
would you be using a big chunky x86 35-amps-at-two-volts processor?

When designing an embedded system it's important to start by looking at
your application rather than by looking at what technologies you
understand and kludging the design to make it all fit.

I think someone needs to tell us what they actually need from a storage
device, and then we can help them, rather than saying 'I need 128M of
somethign exactly like a hard disc' which is clearly a specification
derived from trying to make a desktop system embedded.

kira.

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> When designing an embedded system it's important to
> start by looking at
> your application rather than by looking at what
> technologies you
> understand and kludging the design to make it all
> fit.
> 
> I think someone needs to tell us what they actually
> need from a storage
> device, and then we can help them, rather than
> saying 'I need 128M of
> somethign exactly like a hard disc' which is clearly
> a specification
> derived from trying to make a desktop system
> embedded.


What we wnat is an application that takes about
100-120 MB disk storage space and 128MB memory
footprint on top of linux. This communicates with a
microcontroller which does some image procesing etc.
The criteria for doing image processing is input from
the user to the appln. on linux which inturn gives it
to the microcontroller. All this in a dusty industrial
environment.Amy I have ur sugesstions.
 


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Re: Cf Card vs DiskOnChip

[Alessandro Staltari]

From: "Ramya Ravichandran"
>
>
> What we wnat is an application that takes about
> 100-120 MB disk storage space and 128MB memory
> footprint on top of linux. This communicates with a
> microcontroller which does some image procesing etc.
> The criteria for doing image processing is input from
> the user to the appln. on linux which inturn gives it
> to the microcontroller. All this in a dusty industrial
> environment.Amy I have ur sugesstions.
>

Please take care that if such huge application always have enough memory and
don't need to swap data to disk since flash disk is probably too slow for
this job.
Did you evaluate to remote it using an X-terminal, or mounting an NFS
partition?

Alessandro Staltari
staltari(a)geocities.com

Re: Cf Card vs DiskOnChip

[Ramya Ravichandran]

> (since CFs tend to drop dead unexpectedly).  Neither
> can you build a
> system free of moving parts, since it will still
> need a cooling fan or
> two.  

What about the CF cards used in the pocket PC's  may I
know why u say they need a cooling fan?My friend has
been using a CF card in his pocket PC and is happy
with it that is why I am considering one for my need.



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Re: Cf Card vs DiskOnChip

[Mark Sienkiewicz]

>I'm sorry, I just don't have much respect for people who say things like
>'cost is more important than reliability'.  Probably becasue I've cleaned
>up their messes so often.

This guy is just asking about how to use flash.  He isn't going to include
the entire cost/benefit analysis of his project in the posting, so he just
summarizes it by saying "cost is more important".  There is no reason to
assume that he hasn't thought of the implications of the decision, or even
that he has any other choice.  If you make your product so expensive that
nobody buys it, it is a failure no matter how reliable it is.  Cost is
always an important factor.

>When designing an embedded system it's important to start by looking at
>your application rather than by looking at what technologies you
>understand and kludging the design to make it all fit.

But don't forget labor costs.  If I use a system that I already know
everything about, I don't have to spend time learning about it.
Lots of embedded industrial systems are just desktop PCs or ruggedized
desktop PCs for exactly that reason.  They work just fine, and for
a lower cost than some of the alternatives.

>I think someone needs to tell us what they actually need from a storage
>device, and then we can help them, rather than saying 'I need 128M of
>somethign exactly like a hard disc' which is clearly a specification
>derived from trying to make a desktop system embedded.

I don't think that is clear at all.  You can't tell the architecture of a
system solely by looking at storage requirements.  Maybe he just has a lot
of data.

Mark S.

Re: Cf Card vs DiskOnChip

[David Woodhouse]

rrhsin@yahoo.co.in said:
>    If the price of DOC  is less than the CF+IDE adapter or CF +
> PCMCIA-CF adapter then I guess we will settle for DOC.

OOI, why is it not an option to just use flash chips?

>    Also I dont know which adapter to go for PCMCIA or IDE for CF as I
> am not a h/w person. 

PCMCIA mode is likely to be cheaper - CF cards contain an IDE controller, 
which you can use in PCMCIA mode. No need to have another one one your 
board.

--
dwmw2

RE: Cf Card vs DiskOnChip

[Chris Fowler]

http://www.m-sys.com

-----Original Message-----
From: linux-mtd-admin@lists.infradead.org
[mailto:linux-mtd-admin@lists.infradead.org]On Behalf Of Ramya
Ravichandran
Sent: Saturday, January 26, 2002 1:29 AM
To: Russ Dill; dwmw2@infradead.org; linux-mtd@lists.infradead.org
Subject: Re: Cf Card vs DiskOnChip


> > Doesn't the ROM needed  depend on the application
> than
> > runs on Linux? 
> > 
> 
> you said "serial application". Doesn't seem like
> much to me
> 

Right now I am trying to find out the price of DOC. I
tried the serach words "DiskOnChip" and "DiskOnChip
Price" . The search results explain DOC but don't give
the price.
   If the price of DOC  is less than the CF+IDE
adapter or CF + PCMCIA-CF adapter then I guess we will
settle for DOC.
   Also I dont know which adapter to go for PCMCIA or
IDE for CF as I am not a h/w person.
  


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