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UBL image Boot Image generation using mkimage
This document describes how to set up an U-Boot image that can be directly
booted by a DaVinci processor via NAND boot mode, using an UBL header,
but without need for UBL.
For more details see section 11.2 "ARM ROM Boot Modes" of
Command syntax:
./tools/mkimage -l <u-boot_file>
to list the UBL image file details
./tools/mkimage -T ublimage \
-n <board specific configuration file> \
-d <u-boot binary> <output image file>
For example, for the davinci dm365evm board:
./tools/mkimage -n ./board/davinci/dm365evm/ublimage.cfg \
-T ublimage \
-d u-boot-nand.bin u-boot.ubl
You can generate the image directly when you compile u-boot with:
$ make u-boot.ubl
The output image can be flashed into the NAND.
Please check the DaVinci documentation for further details.
Board specific configuration file specifications:
1. This file must present in the $(BOARDDIR) and the name should be
ublimage.cfg (since this is used in Makefile).
2. This file can have empty lines and lines starting with "#" as first
character to put comments.
3. This file can have configuration command lines as mentioned below,
any other information in this file is treated as invalid.
Configuration command line syntax:
1. Each command line must have two strings, first one command or address
and second one data string
2. Following are the valid command strings and associated data strings:-
Command string data string
-------------- -----------
MODE UBL special mode, on of:
MODE safe
ENTRY Entry point address for the user
bootloader (absolute address) = TEXT_BASE
nand_spl loader.
ENTRY 0x00000020
PAGES Number of pages (size of user bootloader
in number of pages)
START_BLOCK Block number where user bootloader is present
START_PAGE Page number where user bootloader is present
(for RBL always 0)
Structure of the u-boot.ubl binary:
compile steps:
1) nand_spl code compile, with pad_to = (TEXT_BASE +
Example: cam_enc_4xx pad_to = 0x20 + (6 * 0x800) = 0x3020 = 12320
-> u-boot-spl-16k.bin
!! TEXT_BASE = 0x20, as the RBL starts at 0x20
2) compile u-boot.bin ("normal" u-boot)
-> u-boot.bin
3) create u-boot-nand.bin = u-boot-spl-16k.bin + u-boot.bin
4) create u-boot.ubl, size = 1 page size NAND
create UBL header and paste it before u-boot.bin
This steps are done automagically if you do a "make all"
-> You get an u-boot.ubl binary, which you can flash
into your NAND.
Structure of this binary (Example for the cam_enc_4xx board with a NAND
page size = 0x800):
offset : 0x00000 | 0x800 | 0x3800
content: UBL | nand_spl | u-boot code
Header | code |
The NAND layout looks for example like this:
(Example for the cam_enc_4xx board with a NAND page size = 0x800, block
size = 0x20000 and CONFIG_SYS_NROF_UBL_HEADER 5):
offset : 0x80000 | 0xa0000 | 0xa3000
content: UBL | nand_spl | u-boot code
Header | code |
^ ^
^ 0xa0000 = CONFIG_SYS_NROF_UBL_HEADER * 0x20000
0x80000 = Block 4 * 0x20000
If the cpu starts in NAND boot mode, it checks the UBL descriptor
starting with block 1 (page 0). When a valid UBL signature is found,
the corresponding block number (from 1 to 24) is written to the last 32
bits of ARM internal memory (0x7ffc-0x8000). This feature is provided
as a basic debug mechanism. If not found, it continues with block 2
... last possible block is 24
If a valid UBL descriptor is found, the UBL descriptor is read and
processed. The descriptor gives the information required for loading
and control transfer to the nand_spl code. The nand_spl code is then
read and processed.
Once the user-specified start-up conditions are set, the RBL copies the
nand_spl into ARM internal RAM, starting at address 0x0000: 0020.
The nand_spl code itself now does necessary intializations, and at least,
copies the u-boot code from NAND into RAM, and jumps to it ...
Author: Heiko Schocher <>