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

[Sergey Lapin <slapin@ossfans.org>]

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?
> 
> 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.

S.