howto

howto

[Livio Plos]

Hi,

I'm trying to build a system with flash chips instead of an
hard disk or a disk on module and this seems to be the 
most advanced project to help me doing this.

Neverthless, it is not easy to begin understanding how to 
move between sources, configuration, modules...

Can I boot totally from flash without any other storage support?

Is there any howto or high level docs to configure and compile?


Thank you very much.

Livio





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Re: howto

[David Woodhouse]

livioplos@bigfoot.com said:
>  I'm trying to build a system with flash chips instead of an hard disk
> or a disk on module and this seems to be the  most advanced project to
> help me doing this.

> Neverthless, it is not easy to begin understanding how to  move
> between sources, configuration, modules...

Documentation is moving up the TODO list very slowly, as I get the code 
closer to a state where I'm happy with it.

> Can I boot totally from flash without any other storage support?

Yes, as long as you have the flash mapped where the CPU startup vector 
points, or the board's firmware has support for starting the Linux kernel
from flash (RedBoot does).

> Is there any howto or high level docs to configure and compile? 

Drop the latest code from CVS on top of your 2.4 kernel tree. Enable all the
CFI stuff, enable CONFIG_MTD_PHYSMAP and set the address, size and bus width
for your flash mapping appropriately. Boot it and see what happens.

If you want to partition the flash, as most people do, you'll want to copy
one of the other 'map' drivers (eg. pnc2000.c) and change the numbers
accordingly.

--
dwmw2




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mtdchar.c and vmalloc

[Alice Hennessy]

Hello,

During  stress testing,  I ran into a data corruption problem that  went away
after I changed vmalloc to
kmalloc  in mtd_read and mtd_write functions (mtdchar.c).   I added a loop to
the code so that malloc size
doesn't exceed the kmalloc maximum of 128k bytes.
Seems to work fine now.

Does this make sense? Anyone else see this problem?   Any opinions if this is
an ok solution until
kiovec or something else is implemented?

Alice



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Re: mtdchar.c and vmalloc

[David Woodhouse]

ahennessy@mvista.com said:
>   Any opinions if this is an ok solution until kiovec or something
> else is implemented? 

S'fine.

--
dwmw2




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Re: howto

[Michael Stumpf]

Sorry for the slow response; been on vacation.

> Can I boot totally from flash without any other storage support?

I'm doing some work requiring precisely this--flash chips, preprogrammed,
intended to boot linux with a read-only filesystem, preferrably compressed,
from a well-known ROM address.

I originally hacked up mtdram.c to do what has already been done, quite
elegantly infact..

There is a patch out there somewhere (search this list, if you can't find it,
let me know and I'll get it to you.) that adds a block device to the kernel
called "/dev/rom".. it has two modes of operation:

1)  Encodes the binary filesystem image and compiles it directly into the
kernel, bloating its final size

or 2)  Allow you to point it to a "well known" memory address that has (this is
unclear) 4 bytes containing the filesystem size (in bytes), 4 bytes of "00",
and then the filesystem image, whatever that may be.  I use cramfs with great
success on a very memory-constrained target.
 
> Is there any howto or high level docs to configure and compile?

Patch it in, enable it in config, refer to above notes.  Let me know if you're
still lost.

Regards,
Michael


=====
=====================================================================
Michael J. Stumpf                              
LinuxPPC enablement
IBM-Austin, TX     512.838.1524 [lab]  512.838.5335 [work]   
http://www.pobox.com/~mstumpf

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Re: howto

[Bjorn Wesen]

On Wed, 10 Jan 2001, Michael Stumpf wrote:
> > Can I boot totally from flash without any other storage support?
> 
> There is a patch out there somewhere (search this list, if you can't find it,
> let me know and I'll get it to you.) that adds a block device to the kernel
> called "/dev/rom".. it has two modes of operation:

That would be the krom device, I think it was done by the uClinux
guys. It's not necessary for booting from cramfs though, it was made for
hackish support of romfs/mmap's directly to flash without going through
the buffer layer.

> unclear) 4 bytes containing the filesystem size (in bytes), 4 bytes of "00",
> and then the filesystem image, whatever that may be.  I use cramfs with great
> success on a very memory-constrained target.

To do that I just replace cramfs_read with this (romfs_start is defined by
head.S during boot to the place where the cramfs lives):

static inline void *cramfs_read(struct super_block *sb, unsigned int
offset, unsigned int len)
{
	return romfs_start + offset;
}

Then to be able to boot from it, add this to fs/super.c:

#ifdef CONFIG_ROOT_CRAMFS_AS_IMAGE
       void *data;
       fs_type = get_fs_type("cramfs");
       ROOT_DEV = get_unnamed_dev();
       sb = read_super(ROOT_DEV, NULL, fs_type, root_mountflags, data, 1);
       goto mount_it;
#endif

in mount_root just above the CONFIG_NFS_ROOT check.

-BW



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