Booting Linux from Flash

Booting Linux from Flash

[Brendan Simon]

I want to run Linux (linuxppc) on a custom MPC860 board with 32MB DRAM
and 2-4MB of Flash.  This is pure memory mapped flash (not ide
compatible).

What do I need to build and boot an embedded linux system ?

1) Cross Compiler:  I have egcs-1.1b built from the RTEMS build scripts
for powerpc.

2) C libraries:  Do I need these and how are they compiled ?  Is newlib
or glibc required ?

3) Kernenl sources:  How to cross compile ?  Is it as simple as
CC=powerpc-eabi-gcc & make ?

4) What about support executables like init, bash/ash/sh ?  Are the
sources included with the kernel or do I have to get them elsewhere and
compile them with the cross compiler ?

5) I guess I need to write a bootloader.  What does the bootloader have
to do and how do I pass parameters to the kernel ?

6) If I have a root file system image compressed in Flash, how does it
get uncompressed into RAM.  How do I tell the kernel where the root FS
is ?

Thanks,
Brendan Simon.

PS.  Are there any HOWTOs which cover booting from Flash (not Flash IDE
drives).
Ta.


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Re: Booting Linux from Flash

[Brendan Simon]

I would certainly like to get a flash filesystem driver.  I'm not sure if it
is the same thing you are talking about.

I want to boot linux on an powerpc embedded system which has no hard disk.  I
do not want to use lilo.  I imagine that I would have write a simple
bootloader to get the kernel booting.  I want to store the kernel at a known
location in Flash and store a boot image at a known location in Flash.  I then
want to execute the kernel somehow (jump to appropriate address) and pass to
it any parameters required to let it place the boot image in a ram disk.  I
think the kernel lives in the file system so it's a bit of a chicken and egg
problem as far as I can see.  Is the kernel that is booting stored in the boot
image.  If so I guess the boot image has to be uncompressed.  The root
filesystem can be a compressed image though.

Anyone know where I should start with regards to bootloaders or how to get the
kernel booting if I have the kernel and bootimage in Flash somewhere.  Note
the Flash is just memory mapped on a SIMM.  There is no IDE driver or
filesystem on it.  Do I need a Flash device driver ??

Thanks,
Brendan Simon.


John VanLoon wrote:

> I have a driver for a card from advantech. I do not believe that much would
> have to be done to have it usable on a FLASH BOOT BLOCK device. You would
> just need to fill in the details and perhaps add support for multiple
> partitions if you need it (an offset to the beginning is already supported
> allowing booting from compressed image ...) and modify lilo. Let me know if
> you would like such a thing.
> John van Loon
> john.vanloon@oregonchain.com


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Re: Booting Linux from Flash

[Alexander Larsson]

brendan@dgs.monash.edu.au (Brendan Simon) writes:

> I would certainly like to get a flash filesystem driver.  I'm not sure if it
> is the same thing you are talking about.
> 
> I want to boot linux on an powerpc embedded system which has no hard disk.  I
> do not want to use lilo.  I imagine that I would have write a simple
> bootloader to get the kernel booting.  I want to store the kernel at a known
> location in Flash and store a boot image at a known location in Flash.  I then
> want to execute the kernel somehow (jump to appropriate address) and pass to
> it any parameters required to let it place the boot image in a ram disk.  I
> think the kernel lives in the file system so it's a bit of a chicken and egg
> problem as far as I can see.  Is the kernel that is booting stored in the boot
> image.  If so I guess the boot image has to be uncompressed.  The root
> filesystem can be a compressed image though.

The way I'm doing it is i just place the bootcode and a zImage at place in the
flash-mem where the machine boots. Then i just set up the machine and copy the
zImage down to ram and jump to it.

You could probably get it to read a compressed fs image from flash and mount it
as a ram-disk by either using some initrd hacking or doing some kernel startup
modifications.

> Anyone know where I should start with regards to bootloaders or how to get the
> kernel booting if I have the kernel and bootimage in Flash somewhere.  Note
> the Flash is just memory mapped on a SIMM.  There is no IDE driver or
> filesystem on it.  Do I need a Flash device driver ??

No, you don't need a Flash device driver unless you want to write to the flash.

/ Alex



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