[Lenny400] Reviewing the Ingenic board initialisation code

[Dr. H. Nikolaus Schaller]

Hi Paul,

Am 09.06.2015 um 01:52 schrieb Paul Boddie <paul at boddie.org.uk>:

> Hello,
> 
> As you might have noticed, I haven't been looking at the jz4730-related 
> efforts in recent months, but I very recently got back into looking at the 
> initialisation code for the jz4740 (or rather jz4720, as I have a Ben 
> NanoNote), being inspired by the following collection of blog articles about 
> getting code to run on the MIPS Creator CI20 board:
> 
> The CI20 bare-metal project
> http://code.lardcave.net/2015/03/31/1/
> 
> Since the Ben NanoNote has been supported by a U-Boot variant (maybe only 
> really available via OpenWrt), and since Linux kernel support is also present 
> (although that doesn't help with things like PLL and SDRAM initialisation), I 
> thought it might be informative to bring the Ben up without U-Boot using a 
> minimal amount of code (as opposed to using the entirety of the continuously 
> changing beast that is U-Boot).
> 
> So far, I've managed to make a USB bootable stage 1 initialising the PLL and 
> SDRAM (as featured in that blog series) and to glue the framebuffer 
> initialisation code from U-Boot (originally from Ingenic) to a stage 2 payload 
> in order to show a nice pattern on the screen. Figuring out what the USB boot 
> mechanism actually does, and what the limitations really are, is pretty 
> awkward as the blog author found out.
> 
> I'm now intending to extend this work to cover the jz4730 and the Letux 400. 
> It rather looks like the LCD support is mostly the same, and hopefully with 
> some appropriate settings and some SoC-specific adjustments, I can repeat the 
> achievement on the Letux. However, I'm using the USB boot mechanism on the 
> Ben:
> 
> 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.

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 :(

BR,
Nikolaus