Subject: Re: MTD devices in NetBSD
To: marty fouts <firstname.lastname@example.org>
From: Terry Moore <email@example.com>
Date: 03/23/2006 17:48:01
This is true in my experience, too.
At 02:22 PM 3/23/2006 -0800, marty fouts wrote:
>On 3/23/06, Garrett D'Amore <firstname.lastname@example.org> wrote:
> > Terry Moore wrote:
> > > CF cards are done with NAND flash. They don't "know where things
> > > are", they just have an intermediate layer that provides an
> > > abstraction. Due to patents, this is done in a variety of ways.
> > In order to provide that layer, they have to have somewhere to store
> > their persistent data. So they are able to make assumptions about where
> > they can stick stuff on flash.
>You don't have to have that ability, and at least one system doesn't.
>What you have to have is a block signature that uniquely identifies
>the blocks storing the persistent data. With that in place, at boot,
>you scan until you find such a block and go from there. Everything
>you know about the system is relative to the info in such blocks, and
>usually, you duplicate them.
> > If I follow that approach, the end result will be a flash system that is
> > only useful to itself. I.e. you won't have a way to directly access
> > blocks of data at a specific physical sector.
>This is, in fact, how the commercial systems present themselves.
> > This can have bad effects, e.g. for some flash systems which need to
> > store data like bootloaders at a specific offset in flash.
>On NAND, you can't have a bootloader like that. As a minimum, the
>bootloader needs to be able to deal with bad block management.