Two methods to flash the SD Card:
  * image file
  * restore from FSArchive

# Image file

1. Flash the sd card with `dd` utility, wait until this completes. It can take
   awhile as we must wait to sync all the I/O, must also have root access. Replace
   sd* with yours. The `bs` parameter can be adjusted as needed.

$ tar -xzvf rfsoc4x2_casper.img.tar.gz
$ sudo dd if=rfsoc4x2_casper.img of=/dev/sdd bs=32MB status=progress

2. plug sd card into board

# Restore from FSArchive

0. Install fsarchiver (https://www.fsarchiver.org)
  
1. Create two partitions on target sd card (using a tool like gparted)
   - boot partition is usually fat32, has 'boot' flag, at least 300 MB
   - other partition is usually ext4 or similar
   
2. copy contents of `boot/` to the boot partion of the sdcard (replace sd* with yours)
  $ mount /dev/sdd1 /mnt/sdboot
  $ cp -r ./boot/BOOT.BIN ./boot/image.ub ./boot/boot.scr /mnt/sdboot

3 restore the root filesystem using fsarchiver (replace sd* with yours)

   $ mount /dev/sdd2 /mnt/sdrootfs
   $ cd /mnt/sdrootfs
   $ fsarchiver restdir rfsoc4x2_rootfs.fsa ./ -j4 -v
   $ sync

4. plug the sd card into the board