uSD Disconnects; Reset Fails with "CCCCC"; Re-Insert Boots

My Rev.A6 BBB had been running solidly 24/7 for months, with only explainable software-related crashes. But in the last week it has just hung twice, with no relation to software functions, nothing unusual in the logs, and D2/3/4 on solid.

It is powered by an analog regulator from my solar house battery system with huge and redundant battery banks, so there is really no chance of a power glitch. It runs the RCN distro of Ubuntu 14.04, from a 16 GB SanDisk uSD. When it hangs and I press Reset without cycling power, I get no user LEDs, but I do get a series of “CCCCC” characters on the console port.

My A6 SRM says:

CCCC means the SD card is unreadable as a boot source and it cannot read the eMMC either. It is looking for a boot source.


So you are saying that even though it was previously booted from the uSD, and was not power cycled, it would boot from the eMMC if the uSD was not available? I have a fully bootable image on my eMMC, so if it didn’t take over and boot, that would mean something had blocked access to both uSD and eMMC.

Removing the uSD and pressing Reset did not make the eMMC boot, so if your scenario is true the eMMC block survived Reset.

Re-inserting the uSD with no further Reset lets it boot, so what could have been blocking both storage devices that merely inserting the uSD could fix?

I was under the impression that only a power cycle could switch between uSD and eMMC. But SRM 6.8 does sort-of match your scenario:

SRM aside. Gerald was saying that “CCCC…” indicates that no boot-able media was found. if “we” stop and think about this for a minute multiple situations can cause this issue. Not least of which is physical sdcard bracket is loose, and the media over time got screwed inside of it.

I’ve had this happen to me for inexplicable reasoning. I’ve taken the sdcard out, blown it off, and have had it immediately start working again. Why ? No idea . . .