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

[Wolfgang Denk]

Dear Christian Riesch,

In message <BANLkTimhJSs_URkzB-q5y7GQzawSWe005g at mail.gmail.com> you wrote:
>
> > 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.

Thanks for the explanations.

You might want to synchronize your efforts with Heiko Schocher (on
cc:) who might be working on similar things.

Best regards,

Wolfgang Denk

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