  We consider the maximal $\cal{N}-$extended supergravity theory in 3
dimensions with fermionic generators transforming under real but non
necessarily irreducible representations of the internal algebra. We obtain the
symmetry algebra at null infinity preserving boundary conditions of
asymptotically flat solutions, i.e. the maximal $\cal{N}-$extended
super-BMS$_3$ algebra, which possesses non-linear correction in the
anti-commutators of supercharges. We present the supersymmetric energy bound
and derive the explicit form of the asymptotic Killing spinors. We also find
the most generic circular symmetric ground state of the theory, which
corresponds to a non-supersymmetric cosmological solutions and derive their
entropy.
