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RE: Embedded system with RAM Disk

To: Harald Koerfgen <Harald.Koerfgen@home.ivm.de>
Subject: RE: Embedded system with RAM Disk
From: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Date: Thu, 27 Jan 2000 07:53:17 +0100 (MET)
Cc: Victor Wells <vwells@ti.com>, linux@cthulhu.engr.sgi.com, linux-mips@fnet.fr
In-reply-to: <XFMail.000126201529.Harald.Koerfgen@home.ivm.de>
Sender: geert@sonycom.com
On Wed, 26 Jan 2000, Harald Koerfgen wrote:
> On 25-Jan-00 Victor Wells wrote:
> > I am developing an embedded system that will boot from flash.
> > I would like to load a RAM based file system to physical memory
> > and then have the kernel mount the RAM disk as the Root
> > file system.
> [...]
> > 
> > Our boot process is to:
> > 1.) Load the kernel
> > 2.) Load the RAM disk/Root file system
> > 3.) Mount the RAM disk as the Root file system within the kernel
> > 
> > How can I hard code the kernel to know where the RAM disk will
> > exist in physical memory?
> 
> Once upon a time I had a hack which did something similar, linking a ramdisk
> image into the kernel image which resulted in a single file for 
> kernel+ramdisk.
> 
> This is not only a nice feature for installation kernels but a must for boxes
> which are only capable to boot a single file, for example via TFTP.
> 
> The current mechanism, i.e. "addinitrd", works for some boxen which boot ECOFF
> kernel images, but even not for all of them. Creating an kernel+ramdisk ELF
> image and converting that into ECOFF, on the other hand, even works for
> DECstations. Depending on how you fiddle with the linker scripts the ramdisk
> image can easily reside in ROM or flash or whatever.
> 
> Well, somehow this hack didn't make it into the mainstream kernel but came to 
> a
> new life within the LinuxCE project and I am beginning to wonder if we should
> make this the default.

A similar thing is done in Linux/PPC, where the compressed kernel image and
ramdisk are embedded into a new ELF object.

Gr{oetje,eeting}s,

                                                Geert

--
Geert Uytterhoeven ----------------- Sony Suprastructure Center Europe (SUPC-E)
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