Thanks are due to Marcus Roeder, who pointed out an error in my DreamPlug kernel compile workflow (http://rglinuxtech.com/?p=1354)..
The make LOADADDR.. command was incorrect, and would result in less system memory being available..
The correct command is:
make LOADADDR=000008000 uImage
– and this will result in all the memory being available:
# free total used free shared buffers cached Mem: 512648 143796 368852 0 18968 74800 .............
I have amended the original article.. Apologies for the confusion..
Robert Gadsdon. March 29, 2015.