Dear Mr.Wolfgang Denk,
On Wed, Jun 22, 2016 at 8:41 PM, Wolfgang Denk wd@denx.de wrote:
Dear vinoth,
In message CAJst-kGL+cNWys125Y9Xtj=XZvRhStdjnG7cfKMgiQN7dR5=jQ@mail.gmail.com you wrote:
I tried creating the uImage from the vmlinux --but I did not understand what does the -a (load address) and -e (entry point ) points to? I assume that it is the same load address used when loading the kernel image from sd card to RAM.
No, it is not.
There are actually two "load addresses". Uusally I prefer to call the first the "download address": this is the address in memory space where you download the uImage file to, i. e. the first address of the uImage file in the system memory (RAM or parallel NOR flash etc.).
The payload of the uImage is often a _compressed_ kernel image. To boot it, U-Boot will have to uncompress and _load_ it to some other address in RAM. This is the "load address", given by the "-a" option to mkimage. Afther that, you have the uncompressed, executable kerl image sitting in RAM, starting at the "load address" - but this is not necessarily the same as the entry point address - the latter is given by the "-e" argument.
Thanks for your explanation. But I still have some questions , sorry if it is naive:
1) What's the address in the bootcmd corresponds to , I think it is the address where we want the u-boot to load the Linux kernel image into RAM
For ex: fatload mmc 0:1 01000000 bzImage; zboot 01000000
Here 01000000 is the address and bzImage is the compressed Linux kernel stored in mmc0 partition1. Once the Kernel is copied to RAM we are using zboot command to start the kernel, so after it Kernel unpacks itself and starts running
2) I want to use uncompressed Kernel(vmlinux) instead of bzImage. U-boot directly doesn't support running vmlinux, so I need to generate the uImage using the mkImage tool. So the payload in my case in uncompressed kernel. To generate this I want two addresses , load address and entry point address. You have mentioned that the addresses are often fixed. How can I get these addresses?
I am using the same address in bootcmd: fatload mmc 0:1 01000000 uImage; bootm 01000000
While you can download and store the uImage file at an arbitrary address in memory, the addresses for the executable (uncompressed) image and for the entry point are often fixed - this is why they re registered in the uImage file.
Note that because you usually uncompress and load (copy) the image to the load address, you must not download the uImage to the load address; this will usually result in memory corruptuin and boot failure.
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de There is nothing in this world constant but inconstancy. - Swift