Hi Bill,
Just wanted to post a message to close this topic, and maybe help others who may encounter the same problem.
The issue was with the way the Linux kernel works with some older SD cards. Those cards are missing some command and the kernel is unable to read from them. When using a UART serial connection, this problem is reflected as a long series of messages like this on the console:
</s><i>
</i>[ 2.119560] mmcblk0: timed out sending SET_BLOCK_COUNT command, card status 0x400900
[ 2.128134] mmcblk0: command error, retrying timeout
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This kernel bug (actually a misconfiguration) is reported widely on the internet; for example here’s the Ubuntu bug for it: <LINK_TEXT text=“https://bugs.launchpad.net/ubuntu/+sour … ug/1333140”>https://bugs.launchpad.net/ubuntu/+source/udev/+bug/1333140</LINK_TEXT>
The simplest option to avoid this problem is to use a more recent SD Card, one that supports all the eMMC commands. For reference, I got a SanDisk Ultra and that worked perfectly fine.
My Respeaker Core V2.0 board now boots without problem!
Thanks!