[PLUG] booting from a compact flash card

[Keith Lofstrom]

> On Mon, Dec 15, 2008 at 8:48 AM, Keith Lofstrom <keithl at kl-ic.com> wrote:
> > I will have to think about ext2 vs. ext3 vs. "other".  I expect I
> > will set up a boot partition with ext2 (journalling is not needed
> > if the files don't change much), and use some solid-state-friendly
> > file system such as jffs2 for the main partition (or at least
> > /home and /var).  More to learn...

On Mon, Dec 15, 2008 at 09:46:53AM +0800, Cheng Renquan wrote:
> The Linux 2.6.27 has a
> 
> UBIFS is a new filesystem designed to work with flash devices,
> developed by Nokia with help of the University of Szeged
> 
> http://kernelnewbies.org/Linux_2_6_27
> 
> http://www.linux-mtd.infradead.org/doc/ubifs.html
> 
> Think you can try it.

Interesting to know about - but UBIFS is designed to work with
raw flash memory devices, such as the ones in PDAs and cell
phones, not memory products with built-in controllers like
Compact Flash Cards (CF) and Solid State Drives (SSD).  Unless
there is some way to bypass the controller and get at the raw
memory at the erase block level (128Kb or more) I can't use
UBIFS.  Here is "The Big Red Note" from the second document:

   One thing people have to understand when dealing with UBIFS is
   that UBIFS is very different to any traditional file system -
   it does not work on top of block devices (like hard drives,
   MMC/SD cards, USB flash drives, SSDs, etc). UBIFS was designed
   to work on top of raw flash, which has nothing to do with block
   devices. This is why UBIFS does not work on MMC cards or USB
   flash drives - they look like block devices to the outside
   world because they implement FTL (Flash Translation Layer)
   support in hardware, which simply speaking emulates a block
   device on top of the built-in flash chip.

I will be working with either Compact Flash (which has an IDE
parallel interface) or with a SATAII solid state drive.  Those
have built-in controllers and block level ATA interfaces.  
Since UBIFS looks like "The Best Way To Do It", there will
hopefully be standards and devices available in the next few
years that support the raw flash interface, permitting the
use of UBIFS at the consumer level.  

Thanks for the pointer, though.  If I ever work with a device
that provides direct access to the flash (I imagine that
reprogrammable wireless access points, the Google Android,
and other open platforms do) then UBIFS will be very useful.

Keith




-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs