[U-Boot] da850evm: u-boot does not start without UBL since commit f1d2b313c9eb6808d30c16a9eb5251240452a56c

[Christian Riesch]

Hello Wolfgang,

On Mon, Jun 20, 2011 at 3:46 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Christian Riesch,
>
> In message <1308575272-30559-1-git-send-email-christian.riesch at omicron.at> you wrote:
>>
>> On this board, older versions of u-boot (like v2009.11) boot perfectly,
>> even when TI's UBL boot loader is not used (instead the configuration of
>> DDR memory was done using an AIS script). However, since commit
>
> What is AIS ?

I apologize for using that many abbreviations in my mail and not
explaining them :-/

AIS is short for Application Image Script [1]. It is a boot script
that is processed by the ROM bootloader on Texas Instrument's
AM1808/DA850/OMAP-L138 processors. The script allows configuration of
boot modes, PLLs, DDR memory, Pinmuxes etc and loading the an
application like u-boot from flash to RAM and executing it. Using a
suitable AIS one can configure PLL and DDR memory and then directly
start u-boot on these processors, without using Texas Instruments's
user boot loader (UBL) [2].

In the default configuration of the da850evm the boot sequence is like this:
1) ROM bootloader (RBL): starts reading from flash
2) In the SPI-flash, a very simple AIS is present. This AIS tells the
RBL to load the UBL from flash and to start it.
3) The UBL does a lot of hardware initialization and then loads u-boot
from flash and starts it.
4) u-boot does a lot of hardware initialization that has already been
done by the UBL and then loads the Linux kernel.

For my application I would like to get rid of the UBL since most of
the configuration it does is also done by u-boot (although there seems
to be a bug in it) or can be done by AIS (like PLL and DDR memory
configuration), the resulting boot sequence will be:
1) ROM bootloader (RBL): starts reading from flash
2) In the SPI-flash, an AIS is present. This AIS tells the RBL to
configure PLLs and DDR memory and to  load u-boot from flash and to
start it.
3) u-boot loads the Linux kernel.

Hope that helps :-)
Best regards, Christian


[1] Using the AM18xx Bootloader (Rev. A)
http://focus.ti.com/dsp/docs/litabsmultiplefilelist.tsp?sectionId=3&tabId=409&literatureNumber=spraba5a&docCategoryId=1&familyId=1877

[2] https://sourceforge.net/projects/dvflashutils/files