[Lenny400] Reviewing the Ingenic board initialisation code

[Paul Boddie]

On Tuesday 9. June 2015 07.05.04 Dr. H. Nikolaus Schaller wrote:
> Hi Paul,
> 
> Am 09.06.2015 um 01:52 schrieb Paul Boddie <paul at boddie.org.uk>:
> > 
> > http://en.qi-hardware.com/wiki/Boot_Modes
> > http://en.qi-hardware.com/wiki/USB_BOOT_mode
> > 
> > Does anyone know if it is possible to invoke this mode on the Letux, or
> > whether the bootloader supports a “software" variant?
> 
> Not that I am aware of. We might have to develop and install our own U-Boot
> which is a high risk of bricking the device.

Yes, I don't want to do that!

> I remember that I did try to understand how boot works, but it is too long
> ago that I remember details and wasn’t well documented :(

I suppose that it's this thread you're thinking of here:

https://www.mail-archive.com/mipsbook-devel%40linuxtogo.org/msg00181.html

That's where that CI20 blog series is somewhat refreshing because the author 
tries to explain the USB boot process in clear terms in his native English. In 
the past, there has been code available from Ingenic for U-Boot, but their FTP 
site gets cleared out periodically, and even the various mirrors don't always 
have the resources that were once available.

Fortunately, I found the following repository containing U-Boot with jz4730 
support:

https://github.com/shenhaocn/jzcode-x11

There's also a specific U-Boot repository, but I can't see any notable 
differences between it and the other one:

https://github.com/shenhaocn/jz-uboot

I'm sure I've seen boot code before, but I think it's the code in the 2.6 
kernel that detects various keys and supposedly performs NAND-flashing 
operations. It becomes difficult to track all the different resources, 
especially when some of them tend to go away and not always come back, like 
all the kwaak.net ones which even the Internet Archive doesn't have any more.

Ultimately, for the Letux (but also for less awkward NanoNote experiments) it 
may be worthwhile focusing on a payload loaded from SD/MMC media, however.

Paul