[U-Boot-Users] DiskOnChip, filesystems, and other booting options

[Wolfgang Denk]

Dear Udi,

in message <fsrgav0iq16cgicc588ms3p7nvc2gtogbb at 4ax.com> you wrote:
> 
> In an ideal world, I would like the DiskOnChip to be:

Maybe you can find some useful information in  section  ``7.3.  Using
Disk On Chip "Drives"'' at
http://www.denx.de/doc/CPU86/advanced-topics.html#DISK-ON-CHIP

> 1. Partition into one or more partitions

You can use "nftl_format" to crewate a "binary partition"  (which  is
ideal  to  hold  one  or  more  Linux  kernel images) and you can use
"fdisk" to partition the remainder of the DoC in the classical way.

> 2. Boot the kernel from a file in one of the partitions (could be FAT)

Put the kernel in the binary partition, and boot it from there.

Or extend U-Boot and add MSDOS filesystem support.

> 3. mount root from separate partition, (if kernel is on FAT), or same
> partition as the kernel (if possible).

Put the kernel in the binary partition, and mount one of teh  regular
partitions as root filesystem.

> I'm slightly confused as to the status of JFFS2, DOS partitioning, DOS
> FAT/VFAT, and the DiskOnChip support. More specifically:

JFFS2 has nothing to do with  this.  DOS  FAT/VFAT  support  is  non-
existent.

> 1. As far as I can tell, the only DiskOnChip support are the "doc read" and
> "doc write" commands, therefore if I use these commands I must load the kernel
> directly off the raw sectors - no filesystem support whatsoever. Am I correct?

No, you are not correct.

First, the "doc" command provides more sub-commands, like "doc  info"
or "doc erase".

"help doc" helps ;-)


> 2. Does the "doc read" and "doc write" use the NFTL layer, or do they access
> the raw device sectors?

They do not use NFTL. They use raw binary offset addresses.


> 3. As far as I can tell, the FAT support is hardwired to the floppy controller
> device, and the DOS partition support is wired to the IDE support. Am I right?

???


> It seems to me it is quite trivial to construct a simple interface (a struct
> containing the block device geometry, plus a pointer to sector read function),
> and have both the partitioning and the DOS FAT code access this. This could
> help support DOS filesystems on D.O.C, floppies and IDE devices.

Are you talking about U-Boot or Linux here?


> 4. What is the best way to achieve my requirements above? (booting a kernel
> from a filesystem on the D.O.C). Can JFFS2 help me in any way?

See  the  document  mentioned  above.  It  contains  pretty  detailed
instructions. And no, JFFS2 has nothing to do with it.

> 5. Failing all the above, can I partition the device under Linux into 2
> partitions, write down the sector range for the 1st partition, and use it  to
> read/write the kernel using the "doc read" and "doc write interface"?
> I would then mount the 2nd partition after booting the kernel.

Yes, you can do that. See above.


Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
All easy problems have already been solved.