The eMMC was mounted to a host machine using the “interrupt U_Boot and typing ums 0 mmc 0” method and connected using the USB-A to USB-A cable.
So if I understand that, the Le Potato isn running, just making the eMMC card available to the host.
The issue was trying to write the image, created from the 128GB SD card originally used to get the board up and running to the eMMC, which only has 125GB available. That caused dd to fail & hang things up.
After trying unsuccessfully to shrink the image size below 125GB, I gave up and started fresh after agin mounting the eMMC as above. Worked like a charm.
Takeaway: If you plan on installing an eMMC after using an SD card to fire things up, make sure the SD card is smaller than the available space on the eMMC card you’ll be installing.
Question: What is on the Libre 128GB eMMC card that eats up 3GB? and can that be cleared out so an entire image sourced from an SD card of the same capacity could have been made to work?