AT91Bootstrap + Linux kernel for a custom board - docs?

Discussion around products based on ARM Cortex-A5 core.

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arudzins
Posts: 10
Joined: Tue Oct 03, 2017 11:29 am

AT91Bootstrap + Linux kernel for a custom board - docs?

Tue Oct 03, 2017 11:48 am

Hi,

I'm trying to port Linux to a custom module based on SAMA5D27. I'd like to use AT91Bootstrap as the 2nd level bootloader and have it load the kernel.
My problem is that the build seems to depend heavily on the target board, and my target is not any of the predefined Atmel's boards.
Could you, please, point out where to find some documentation that would allow to prepare a build for a custom target in a conscious way?

Best regards,
Adam
blue_z
Location: USA
Posts: 1560
Joined: Thu Apr 19, 2007 10:15 pm

Re: AT91Bootstrap + Linux kernel for a custom board - docs?

Wed Oct 04, 2017 12:08 am

arudzins wrote:I'm trying to port Linux to a custom module based on SAMA5D27. I'd like to use AT91Bootstrap as the 2nd level bootloader and have it load the kernel.
AT91Bootstrap can be configured to do that and that SoC has enough SRAM.
But that's a boot optimization that IMO is ill suited for bringing up a custom board.
arudzins wrote:My problem is that the build seems to depend heavily on the target board, and my target is not any of the predefined Atmel's boards.
Could you, please, point out where to find some documentation that would allow to prepare a build for a custom target in a conscious way?
Some people advocate that "code is the documentation".
Does your board deviate that far from the reference design that existing code cannot be used as a starting point?
IMO you would be better off adhering closely to the reference design or else spend time using a web search engine.

AT91Bootstrap has been around for a decade, and its capabilities has evolved. Atmel had an Application Note on the AT91Bootstrap, but apparently considers that document outdated and no longer listed at its site. Element14 still has a copy: https://www.element14.com/community/doc ... ontrollers
IIRC there is an Atmel app-note on customizing U-Boot.

Good luck
arudzins
Posts: 10
Joined: Tue Oct 03, 2017 11:29 am

Re: AT91Bootstrap + Linux kernel for a custom board - docs?

Wed Oct 04, 2017 8:32 am

Thank you for the reply. The app note seems very informative, it's a pity they don't have a similar one for their newer CPUs.

Of course, my design is partly based on reference design, in this case it was the SAMA5D2-Rev.B-Xplained-Ultra board. So I have essentially the same power supply, the same oscillators, but that's basically it. I have a different type of dynamic RAM (DDR2 instead of DDR3), different NVM (eMMC instead of NAND flash), and different set of differently mapped peripherals.

I'd expect that the config for AT91Bootstrap would allow me to simply choose all that stuff. But instead, the first thing I have to choose is the board, which fixes some important choices. Like, when I choose Xplained, I get correct quartz (12MHz), but incorrect memory (forces DDR3), when I choose other board, I get DDR2, but end up with 24MHz quartz, etc. I tried to prepare a config for my board, but then compilation has a lot of problems (most likely due to some things which I didn't define). Maybe the "make menuconfig" approach is the problem here.

I agree that code often is a good or the best documentation, but in this case the code is too complicated. Without good docs on what should be provided, this is basically a guessing game. AT91Bootstrap doesn't do a lot, so this list should be relatively short and simple.

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