[U-Boot] mx28: booting u-boot via USB

[Matthias Fuchs <matthias.fuchs@esd.eu>]

On 31.01.2012 15:25, Sergey Lapin wrote:
> On Tue, Jan 31, 2012 at 03:03:55PM +0100, Matthias Fuchs wrote:
>> Hi,
>>
>> I have a problem booting the current u-boot-imx version
>> on a MX28EVK via USB. The i.MX28 CPU supports a special boot mode
>> where the image (sb boot stream) is downloaded via USB device
>> (all DIP switches in position 'off' on the EVK). The
>> CPU's internal bootrom implements a HID device in this mode.
>> Freescale provides a download tool "sb_loader" for this purpose.
>> There is also a GPL'd implementation based on libusb.
> Could you please provide link to GPL tool?
check http://svn.rockbox.org/viewvc.cgi/trunk/utils/imxtools/

The code builds fine against a recent version of libusb. I tested it
against the mx28evk.

>>
>> So back to my problem:
>>
>> I build u-boot from the u-boot-imx repository. This runs fine
>> when booting from SD/MMC or SPI-flash. But the console stays dark
>> when using the USB download mode. USB download works fine with the
>> Freescale provided U-Boot sources together with the imx-bootlets
>> SPL code.
>>
>> Now I digged a little bit deeper to find out the cause:
>>
>> When downloading via USB I saw the SPL running correctly.
>> board_init_ll() (arch/arm/cpu/arm926ejs/mx28/start.S) runs through
>> correctly. Then control is passed back to the bootrom. That's
>> where things end as far as I can see.
>>
>> The 2nd stage of u-boot is not started.
>>
>> The USB boot mechanism is not documented that detailed.
>> Is it possible that the SPL code overwrites the bootroms ivt and
>> in consequence crashes the bootrom's USB code? Any further ideas?
> I'd look at difference in linking scripts and addresses in
> freescale u-boot and new u-boot.
> This might be some memory addressing issues. Had some of this with
> i.MX23. Also, some hardware might be not powered on or is powered
> off by SPL.
That's a good catch. I will check Fabio's idea in just a minute.

Matthias