>   It looks like the ffs module does not know how to create / on
> the ramdisk (md0a) AND/OR expects a filesystem to be ready when
> it accesses the device.

It's the latter.  A file system image should alread be in place,
and you typically place it there with mdsetimage.  It might prove
useful to see how the various bits are put in place by the setup
down in e.g. distrib/evbarm/.

Regards,

- H=E5vard