Flash and EWF

[oiccicny]

Newbie asks:
I want to run an App onWindows XPe, where both are stored on a flash device
that has a hardware write protect switch. The App allows you to download and
execute a second app which will also be stored in the same flash device.
Neither app makes any changes to the run time image. My questions are:
1) Is EWF or FBWF required? Could the OS boot and run from the flash device
if the hardware write protect is enabled without using EWF?
2) Does EWF or FBWF need to be built into the XPe kernel, or is it an some
sort of APP that rides on top? I will not be building the OS portion myself -
it is being supplied by another party. Will they need to include EWF and the
API functions as part of the kernel using TargetDesigner? Or can I add it
later as the app programmer?
3) In order to save the second app to the flash, I would have to first
disable the hardware write protect, then do a EWF commit of the downloaded
file. Is this correct? What happens if I do a commit and the hardware write
protect is still enabled?
4) I assume that I will need to use EWF Ram Reg mode?

Thanks.
(e-mail address removed)

 

[Sean Liming]

FBWF is the better option since it allows you to add a write through section
for files and folders and still protect the rest of the OS.

FBWF must be built in since it is a driver. There is an API set and a
command line utility available to control FBWF-
http://www.seanliming.com/Docs/Articles/FBWF_API.pdf. These don't have to be
in the system.

EWF does add some complexity, but could also be used. EWF with RAM-REG with
a commitanddisable -live option could work.

Regards,

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

 

[Srikanth Kamath [MSFT]]

1) Is EWF or FBWF required? Could the OS boot and run from the flash device

if the hardware write protect is enabled without using EWF?

Windows cannot boot from a read-only partition, you would need a write
filter (EWF / FBWF) to simulate read-write behavior

2) Does EWF or FBWF need to be built into the XPe kernel, or is it an some
sort of APP that rides on top? I will not be building the OS portion myself -
it is being supplied by another party. Will they need to include EWF and the
API functions as part of the kernel using TargetDesigner? Or can I add it
later as the app programmer?

Yes , they will need to include EWF / FBWF in the target image using Target
Designer. It is no different from adding any component.

3) In order to save the second app to the flash, I would have to first
disable the hardware write protect, then do a EWF commit of the downloaded
file. Is this correct? What happens if I do a commit and the hardware write
protect is still enabled?

Yes. You need to disable write protection and then do <ewfmgr -commit> to
commit changes to disk. Without this the writes would fail (like on any read
only media)

4) I assume that I will need to use EWF Ram Reg mode?

With RAM REG all configuration info is in the registry and you don't need to
deal with a second partition for storing EWF configuration.