I got a big doubt on MLO and U-boot.

Hi,

VISWANATH KONDAPALLI said:

1. WHY MLO and U-boot ..is there any specific reason in splitting 2 stages of booting ???

AM335X has only 128kB of internal memory. This is by far insufficient to load U-boot.

VISWANATH KONDAPALLI said:

    (1)    I read like memory constraint ?? that internal memory is enough to hold both MLO and U-boot.

See above answer.

VISWANATH KONDAPALLI said:

    (2)  The above document name mentioned saying MLO load U-boot to DDR.  

Yes, this is correct for the same reasons as above.

Hello Biser,
I understand that the internal memory cannot hold the U-boot as its 128kb.. But why the boot ROM code cannot load u-boot directly??? What is the specific reason that it loads MLO and then U-boot??

Regards,
Sanju.

ROM code has no way to determine what type of DDR memory is attached to the device. DDR configuration and timing settings are done in MLO, only after that can U-boot be loaded.

Thanks Biser, but again!!! any specific reason why ROM code cannot determine this ?? Sorry if this is too basic.. :)

Regards,
Sanju.

Let's take AM335X as an example. On this processor you have the possibility to attach mDDR, DDR2, DDR3 or DDR3L external RAM. Each of these can come in different speed grades and sizes, and be run at different clock rates. Then there is software leveling for DDR3 to be taken care of, which includes PCB layout information. There are simply too many combinations and variations to be taken into account. This is a task that is too complex (not to say impossible) to be handled by a simple ROM bootloader. You can check the DDR configuration wiki pages to understand what's involved in the DDR configuration process:
processors.wiki.ti.com/.../AM335x_EMIF_Configuration_tips
processors.wiki.ti.com/.../AM335x_DDR_PHY_register_configuration_for_DDR3_using_Software_Leveling

Hi Biser,

One more request Biser. i am doing code walk through of MLO related code in u-boot/arch/arm/cpu/armv7/am33xx, in this i got all initialization code, but we didnt able to find "MLO loading U-Boot" code/ path where it is processing -- could you please help me in this.

regards,

Viswanath K

Sorry, I'm not a software expert. I will ask the SW team to answer this.

Hi,

Have a look at start.S, lowlevel_init.S, crt0.S files.
Also grep your code for the board_init_r() function.

Best Regards,
Yordan

Hi Yordan,

Thanks for the reply. i gone through those files : these files are in arch/arm/cpu/armv7:
start.s --- which doing cpu intilisation , mmu disable etc.
lowlevel_init.s -- another cpu initilisation functionality.

other files resides in arm/lib folder: crt0.s and board.s -- these are giving the start-up of u-boot from MLO.

Now i am stepping to U-boot : in u-boot i mainly looking for the linux kernel image loading functionality.
i worked on nand-booting -- i done only intilisation calling only -- remaining the code in u-boot for NAND is taken care.

So i like to dig in to the u-boot in the path : board/ti/am33xx folder for the functionality --
1. where the kernel image is read from sd-card and
2. where it is going to decompressing the image.

regards,
Viswanath K

Hi,

That would be the boot command (bootm.c).
Check common/board_f.c, common/board_r.c & the boot command source file common/bootm.c

Best Regards,
Yordan