Historical and custom UEFI boot images may be stored in Flash at address `0x0BFC0000'. Older version of UEFI have been known to cause issues when booting newer deliverables. When Juno fails to boot we recommend one of the first things you try is to erase the Flash like so:
Base Area Size Blocks Block Size
---- --------- ------ ----------
0x08000000 65280K 255 256K
0x0BFC0000 256K 4 64K
Flash> eraserange 0x0BFC0000
Alternatively you can erase everything in Flash, which will also force the board to reflash everything from the MMC card on the next power cycle:
There may be occasions when the MMC card becomes corrupted, causing a failure to reflash and/or reboot the Juno. When this occurs it may be necessary to reformat the MMC card.
Connect a USB-B cable between your host PC and the Juno board, then mount the MMC card on your host PC:
Then reformat the MMC card as FAT16.
Alternatively you can remove the MMC card from the Juno and use a card reader to mount it on your host PC, then reformat it.
We've had reports of a number of Juno boards either powering down or hanging indefinitely upon entering U-Boot / EDK2 when using Linaro release 16.03 onwards; in some cases this is due to a miscalibrated thermal sensor triggering the system control processor's thermal protection shutdown mechanism, causing it to remove power from the A-class processors.
To fix this, unplug the Juno board for at least 60 minutes and enter the following command:
Then unplug the Juno board before powering it up again; it should now successfully boot.
Note: Simply power cycling the Juno board after issuing `Cmd> recal' is not sufficient; you must physically unplug the board.