EWF and FBWF Newbie Questions

[Guest]

Hi All~

I am hoping someone out there will have time to answer a couple newbie
questions for me about EWF / FBWF from a conceptual standpoint. I am new to
XPe coming from the WINCE world.

In Windows CE, I worked on a number of flash based OS devices. These used
3rd party utilities to manage the flash RAM. In one case I used Intel's PSM
and in another a similar tool from Datalight. The idea was two fold. The
first was protection. We had a protected area of flash for a base OS image,
plus a semi-protected area for the registry (required explicit flushing to go
from RAM to the solid state media), and finally, a completely read/write
enabled area for user and application data.

I sort of see how EWF and especially FBWF can fill the bill here so to
speak. Though I am a little fuzzy on both the usage of a page file, and, the
RAM requirements for EWF (sounds like maybe you must have the same amount of
RAM as you do EWF protected flash space?). What I don't see is the second
purpose of the flash management in WinCE. By that I am talking about
low-level wear leveling on the media. What component or driver in XPe
prevents us from prematurely wearing out the flash, besides simply trying to
minimize writes to it? I don't see any "scatter write" functionality unless
I am missing something.

Thanks in advance to anyone who takes the time to answer my query. I know I
am probably asking very elementry questions at this point, but we all have to
start somewhere right? I did read the MSDN intros on both EWF and FBWF so
while I am all for links to other docs, unless I missed something I did not
see the answers to my questions there specifically.

~Bill

 

[Sean Liming \(MVP\)]

Welcome to the operating system that works!

XPE runs off sector based disk just like XP Pro does. Windows CE requires
special drivers because it can execute in place (XIP) out of flash. With
XP/XPe access to a disk is already built in.

XP/XPe contastantly access the disk, even when you are not doing anythin on
the computer, this can wear down a flash disk. Wear-leveling has to be built
into the disk level since it is not part of the operating systems. You will
see many topics on booting XPe from flash disks; notably CF and USB flash
disks. CF cards come in different flavors - some support wear-leveling many
don't. http://www.seanliming.com/flashhelp.html.

EWF and FBWF can be used to protect the life of the flash, but can be
controlled so you can still update the OS. They also provide protection in
case of sudden power outage.

--
Regards,

Sean Liming
www.sjjmicro.com / www.seanliming.com
Book Author - XP Embedded Advanced, XP Embedded Supplemental Toolkit

 

[Guest]

Thanks Sean. FYI I just picked up a copy of your book via Amazon. Am sure
it will help. I looked at the website you pointed me too and very few of
those flash cards explicity stated built-in wear-leveling. If it doesn't say
do I assume its not there? Also, what about memory requirements? Does EWF
in a worst case scenario have a one to one relationship with system RAM? In
my application, we have a bit of debug logging, registry manipulation, and a
local SQL-Lite db that all require write access. Everything else I don't
care about. Is the idea of the EWF model such that I would create a
non-filtered partition for this info, then run everything else on an EWF
protected drive? Again, sorry for my ignorance on the subject. I do feel
though like I am slowly getting my head wrapped around the concepts.

 

[Sean Liming \(MVP\)]

1. CF - I suggest that you contact the CF manufacturers directly to get more
information. I can tell you that SanDisk doesn't support embedded, but
WinSystems, PQI, etc. have solutions that will work with XPe.
2. RAM / EWF- The application memory needs are something your have to test.
You are getting the concept. If you are using a database and not using HORM,
then I suggest FBWF since it will allow you to control the amount of RAM for
the overlay and allow a write -through section for your database files.

Regards,

Sean Liming
www.sjjmicro.com / www.seanliming.com
Book Author - XP Embedded Advanced, XP Embedded Supplemental Toolkit

 

[fdbbern]

I can recommend the Compact Flash from Silicon Systems. It has been very
reliable for us and it works great with XPe.