RBL, UBL , PSP Boot loader
sudhakar.raj at ti.com
Thu Sep 11 23:37:57 CDT 2008
Find my answers inline.
From: davinci-linux-open-source-bounces at linux.davincidsp.com [mailto:davinci-linux-open-source-bounces at linux.davincidsp.com] On Behalf Of Nitin Mahajan
Sent: Friday, September 12, 2008 9:28 AM
To: davinci-linux-open-source at linux.davincidsp.com; Gole, Anant
Subject: RE: RBL, UBL , PSP Boot loader
--- On Thu, 11/9/08, Gole, Anant <anantgole at ti.com> wrote:
> From: Gole, Anant <anantgole at ti.com>
> Subject: RE: RBL, UBL , PSP Boot loader
> To: "nitinm76 at yahoo.com" <nitinm76 at yahoo.com>, "davinci-linux-open-source at linux.davincidsp.com" <davinci-linux-open-source at linux.davincidsp.com>
> Date: Thursday, 11 September, 2008, 7:23 PM
> The terms are are as follows:
> 1. RBL - Rom bootloader - embedded in the chip
> 2. UBL - User boot loader - NOT in the chip - RBL boots UBL
> (except for NOR and UART boot modes) which boots a secondary
> bootloader. There are size constraints on what RBL can boot
> and since most secondary bootloaders do not fit in the size
> UBL is required - provided by PSP
> 3. UBoot - secondary bootloader that PSP provides -
> typically used to boot linux kernel.
> When someone says PSP Bootloader it could mean either UBL
> and UBoot and both are NOT in the chip - they are on the
> external NOR/NAND memory.
> I assume you have seen the app note "Booting DaVinci
> EVM from NAND Flash" which explains the procedure of
> using UBL/uBoot:
TI UBL Version: 1.12, Flash type: NAND
Booting PSP Boot Loader
PSPBootMode = NAND
Starting NAND Copy...
Initializing NAND flash...
Valid MagicNum found.
NAND Boot success.
U-Boot 1.3.1 (Jun 12 2008 - 12:21:54)
So the above set of messages while booting, indicate that
1. A TI UBL version 1.12 was booted by the RBL, and the UBL was loaded from NAND?
2. "Booting PSP Boot Loader PSPBootMode = NAND" , PSP bootloader here means the U-Boot, which will also be loaded from NAND?
[Sudhakar] Yes, here PSP bootloader means U-Boot and U-Boot is also stored in NAND.
3. This u-Boot inturn would load the Linux kernel from NAND?
[Sudhakar] Linux Kernel may not be stored in NAND. U-Boot can download the Linux Kernel Image using tftp. Linux Kernel Image can be stored in NAND, in that case the bootargs and bootcmd has to be set correctly in U-Boot.
4. Most importantly , how will UBL know from which place on NAND to load the u-Boot?
[Sudhakar] UBL is designed in a way to look for a particular magic number which is specific to any application, in this case, the application being U-Boot. Also while writing the U-Boot image to NAND; a header will be pre-pended to the image which will have the information regarding the page and block number where the u-boot image will be stored on NAND (Magic number is also part of this header). Based on this information, UBL will be able to read from NAND to RAM and start executing.
How will u-Boot know from which place to load the Linux kernel, since NAND is not a Random access device?
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