my %other_hash=(
                param1 => val1,
                param2 => val2
                );
my %hash=(
          key1 => value,
          key2 => \%other_hash
          );

##</code><code>##

my %hash=(
          key1 => value,
          key2 => (
                   param1 => val1,
                   param2 => val2
                  )
          );