Loading Linux from already running code..

Hi All,
I need some suggestions for booting Linux( >2.6.30 ) with my new project.
Scenario:I've a custom built board with PowerPC 440 + 256 MB RAM. there is NO FLASH on this board.There is a hardware logic which will get an initial piece of code (through hardware network) into the ram and then execute it. This code does mandatory initialization of a proprietary chip and this code MUST execute on power on. any other images (Linux image or ramdisk) can be loaded any specified area in the memory along with this code.
My requirement is to boot Linux at the end of the this initialization.
what is the best way to do it? 
1. Will it be possible to transfer control to a simpleImage.initrd.myboard.elf(or .bin ..?!)  image from already_existing_code?2. Should I use u-boot and then load uImage, ramdisk and the dts blob? Using u-boot will reduce the effort?3. Is there any other way to approach this??


Regards,Sumesh 		 	   		  

You could build a tarball containing the root files system, dtb, Linux,
plus a header indicating where the different pieces need to be loaded.
Then your initial code loads the different parts at the right memory
locations, sets up the Linux arguments, and jumps to Linux.

-Carlos

On Sun, 2011-09-25 at 18:47 +0000, Sumesh Kaana wrote:

Hi All,


I need some suggestions for booting Linux( >2.6.30 ) with my new
project.


Scenario:
I've a custom built board with PowerPC 440 + 256 MB RAM. there is NO
FLASH on this board.
There is a hardware logic which will get an initial piece of
code (through hardware network) into the ram and then execute it. This
code does mandatory initialization of a proprietary chip and this code
MUST execute on power on. any other images (Linux image or ramdisk)
can be loaded any specified area in the memory along with this code.


My requirement is to boot Linux at the end of the this initialization.


what is the best way to do it? 


1. Will it be possible to transfer control to a
simpleImage.initrd.myboard.elf(or .bin ..?!)  image from
already_existing_code?
2. Should I use u-boot and then load uImage, ramdisk and the dts blob?
Using u-boot will reduce the effort?
3. Is there any other way to approach this??






Regards,
Sumesh
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On Mon, Sep 26, 2011 at 7:26 PM, Carlos Munoz [off-list ref] wrote:

You could build a tarball containing the root files system, dtb, Linux,
plus a header indicating where the different pieces need to be loaded.
Then your initial code loads the different parts at the right memory
locations, sets up the Linux arguments, and jumps to Linux.

That is exactly what the firmware-independent simpleImage.initrd.*
targets already do. The resulting elf file include the dtb and initrd
as well as a prompt-like boot arg cli.
I think it will be possible to just place the simpleImage.initrd.*
into you memory and let the existing code jump to the start adress of
the elf image. I managed to start a ppc core using JTAG and the
simpleImage.initrd elf files and I think the procedure is very much
the same but instead of the JTAG debugger setting the PC to the start
address, your startup code has to do it.


Philipp

Hi Philipp and Carlos,

Thanks for the reply.

When simpleImage.elf is loaded by a debugger, the debugger reads the elf image header and places various sections of image into right place in the RAM. But when I do it from already_running_code, I should manually unpack the elf and place the sections in the memory, then jump to the start address, Am I right?

Also,
Is it possible to load a simpleImage.bin file and jump to the start address using a function pointer, Hence I can avoid unpack_elf_image()...? - Will this work?


Thanks,
Sumesh.

Date: Mon, 26 Sep 2011 20:13:24 +0200
Subject: Re: Loading Linux from already running code..
From: p.ittershagen@googlemail.com
To: cmunoz@sablenetworks.com
CC: linuxppc-dev@lists.ozlabs.org; sumeshkkn@hotmail.com

On Mon, Sep 26, 2011 at 7:26 PM, Carlos Munoz [off-list ref] wrote:

quoted

You could build a tarball containing the root files system, dtb, Linux,
plus a header indicating where the different pieces need to be loaded.
Then your initial code loads the different parts at the right memory
locations, sets up the Linux arguments, and jumps to Linux.

That is exactly what the firmware-independent simpleImage.initrd.*
targets already do. The resulting elf file include the dtb and initrd
as well as a prompt-like boot arg cli.
I think it will be possible to just place the simpleImage.initrd.*
into you memory and let the existing code jump to the start adress of
the elf image. I managed to start a ppc core using JTAG and the
simpleImage.initrd elf files and I think the procedure is very much
the same but instead of the JTAG debugger setting the PC to the start
address, your startup code has to do it.


Philipp
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Linuxppc-dev@lists.ozlabs.org
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