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RE: root fs on flash which is not mapped in memory




> -----Original Message-----
> From: owner-dev-etrax@xxxxxxx.com]On">mailto:owner-dev-etrax@xxxxxxx.com]On
> Behalf Of Pieter Grimmerink
> Sent: maandag 6 mei 2002 22:21
> To: dev-etrax@xxxxxxx.com
> Subject: root fs on flash which is not mapped in memory
> 
> 
> What would be the implications when using something like a
> flashcard, something with an interface rather then being
> mapped in the memory address range with the etrax 100 LX?
> It would have to contain the root fs.

Let me answer my own questions here, I found out a bit more
since I typed this, maybe this can be of any use for others:

> -I guess I need to have a flash device that has an mtd driver
> written for it, or at least has a read/write/erase sector
> interface so that an mtd driver could be written for it?

Flash which is not mapped in memory is called NAND flash,
there are mtd drivers for several NAND flashes, DiscOnChip
being one of them.
 
> -I probably need to have a small (how large?) flash device
> mapped in the address range, to contain a kernel with
> devicedriver for the flashcard?
> Or could a small bootloader be written to get an image 
> containing the actual kernel, directly from the flashcard?

DiscOnChip can behave like a bootsector, loading and booting
an image on the device itself.
Rumours go that the GNU GRUB bootloader can be patched to
replace the standard DiscOnChip firmware, and boot linux directly
from DiscOnChip.

> -other issues that have to be taken care off, before such
> flash devices can be used to host a root fs?

I'd prefer having JFFS2 on this device, rather then using FTL or
whatever is standard for DiscOnChip.
As far as I understand, NAND flash is supported by JFFS2
since recently, it's rumoured to be almost reaching
beta status.

I have not found any success stories from people using
JFFS2 on DiscOnChip though.

Best regards,

Pieter Grimmerink