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

Dear Christian Riesch,

In message BANLkTimhJSs_URkzB-q5y7GQzawSWe005g@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