Thanks @all for the helpful input! I actually got the "unlocking" of the DRAM done, so I can read and write to it from USB downloader mode - it's essentially a copy of yifanlu's / Amazon's commands.
Next problem is: when I try to access it from u-boot, the data isn't there anymore.
I'm heavily customizing the u-boot image now to understand what might be happening. I even disabled DRAM initialization in the u-boot code, so that u-boot crashes (hangs) unless the memory had previously been initialized using USB mode. This works "correctly" - in the sense that if (and only if) I initialize the DRAM prior to launching u-boot, the device will actually boot. So since u-boot should not be messing with the DRAM (at least not too much), I don't understand why my data is always getting lost. I tried to put it at the beginning of the DRAM, at the "end", etc - no luck. I'm now even trying to scan the entire address space, because it could just have been "logically" relocated somewhere - no luck either.
Hell, all I want to do is
- Put data at 0x7whatever before launching u-boot
- In uboot, "bootm 0x7whatever"
If it was working, this would be the easiest solution to simply upload a kernel and run it, so that we could focus on the actual kernel/initrd (= "almost userland") functionality instead of all the bootstrapping.
@eureka: I'll look at the newest links you provided, thanks!
@knc1/geekmaster: I looked into the k3launcher thread - actually I read all of it - but I still don't know whether it can also handle K4/K5. In the long run, it would definitely be best to have a single tool which can handle the needs of all devices. For the time being, I'll stick with the imx_usb because I now understand what it is doing and how to use it (this does not go for the Kindle beast though
).
Again, any help is more than welcome.