Comment 16 for bug 708883

I examined the pandaboard schematics and found that the SYS_BOOT[7..0] pins are set to 10000101 by default. These control the actions of the ROM on the OMAP4. b5..b0 select the boot ordering; 000101 means try USB boot first and MMC1 second.

In the case that no external power is connected to the USB OTG, the ROM skips initializing the USB unit and boot proceeds normally via MMC1.

In the case that there is external power coming to the USB OTG connector, the ROM spends a few seconds trying to bring that up and if it isn't satisfied then proceeds to the second boot option via MMC1. It starts the MMC1 card clock and pulls in X-loader and it starts.

However because of some side effect of the ROM having followed a boot path that started the OTG unit, X-loader is unable to operate normally at a couple of points during its initialization.

I have just sent some patches to linaro-dev that fix this for me so I am able to boot into Linux OK just from my laptop plugged into the OTG socket on Panda.