There are now two implementations for LXRT:
- lxrt.c.noktrd, using the bottom half approach to make a task hard real time,
  as described in Documentation/README.LXRT;
- lxrt.c.ktrd using kernel threads support to make a task hard real time, as
  done in NEWLXRT.
The choice between the two is made at menuconfig, the default being lxrt.c.ktrd.
