Dingux News - Baffling dual-boot bug

Booboo posts yet another update of his work on linux for the Dingoo A320:

There's one dual-boot bug that keeps me utterly baffled. I'm not sure if this is happening to others beside me because it involves the serial console connection. I'll describe it here with the dual purpose of confirming that it happens to others and requesting suggestions:

1- Install dual boot.
2- Plug the USB cable (either connected to a PC or just to the wall charger).
3- Reset the device while holding SELECT pressed.

The SPL dingux splash screen appears but it does not boot dingux, just hangs there. If you perform the same procedure but without the USB cable connected dual boot works file.

So what's so baffling and why didn't I notice this before?

It boots fine if the serial console cable is connected. And that's the cable one needs to see what's going on during the boot process. So if I connect it the problem dissapears, and if I don't connect it I can't see what's going on.

Question is: does this happen too to those that haven't installed the serial console?.

It may be that the SPL code fails to load u-boot, or that the u-boot code fails to load zImage. One could think that maybe the u-boot code is receiving some stray input from the unconnected serial console and stopping to wait for more input, but then, why does this happen only when the USB power is plugged?.

Looks like the only way to investigate this is to modify the SPL and u-boot sources to output debug stuff to screen.

UPDATE 1: just don't know why I didn't think of it before. I just connected the serial console AFTER the boot hangs and confirmed that u-boot has received some garbage input and is sitting there like a stupid waiting for further instructions. I'm not sure how the USB power applied is causing this garbage in the serial input when it's undriven, but that is definitely what's happening. The fix should be dead easy: modify u-boot to completely ignore any input.

UPDATE 2: fixed, should go in the next dual-boot release. Unless people reports this is causing problems, I'll wait until I make some other pending changes into the dual boot to make the release.

http://www.dingux.com/2009/07/baffli...-boot-bug.html