Config the mount points

Doesn't this explain it?

/dev/root on / type romfs (ro)

You can't write to a read-only filesystem. :-) romfs's will always be read-only. /var and /tmp are, likely, ramfs and they are labeled as rw in the returned list from your mount command.

If you want a larger filesystem to play with, you might consider using nfs or (if it works) smbfs to your host PC during development. In that way, you can compile and test code by just copying it to a Windows "share" or an NFS export.

Cheers,

- slacker