diff --git a/drivers/wireless/ieee802154/Kconfig b/drivers/wireless/ieee802154/Kconfig
index 4a799e4999..df4a1796a0 100644
--- a/drivers/wireless/ieee802154/Kconfig
+++ b/drivers/wireless/ieee802154/Kconfig
@@ -16,6 +16,7 @@ source drivers/wireless/ieee802154/mrf24j40/Kconfig
 config IEEE802154_AT86RF233
 	bool "ATMEL RF233 IEEE 802.15.4 transceiver"
 	default n
+	depends on EXPERIMENTAL
 	---help---
 		This selection enables support for the Atmel RF233 device.
 
diff --git a/include/nuttx/net/sixlowpan.h b/include/nuttx/net/sixlowpan.h
index 457044bca1..de272839e8 100644
--- a/include/nuttx/net/sixlowpan.h
+++ b/include/nuttx/net/sixlowpan.h
@@ -262,7 +262,9 @@
 
 #define SIXLOWPAN_MAC_STDFRAME 127
 
-/* Space for a two byte FCS must be reserved at the end of the frame */
+/* Space for a two byte FCS must be reserved at the end of the frame.
+ * REVISIT:  True for IEEE 802.15.4, but not for some other packet radios.
+ */
 
 #define SIXLOWPAN_MAC_FCSSIZE  2
 
diff --git a/sched/sched/sched_verifytcb.c b/sched/sched/sched_verifytcb.c
index 5958b28e0c..6dd93b6a29 100644
--- a/sched/sched/sched_verifytcb.c
+++ b/sched/sched/sched_verifytcb.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  * sched/ched_verifytcb.c
  *
- *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2009, 2017 Gregory Nutt. All rights reserved.
  *   Author: Gregory Nutt <gnutt@nuttx.org>
  *
  * Redistribution and use in source and binary forms, with or without
@@ -59,8 +59,29 @@
 
 bool sched_verifytcb(FAR struct tcb_s *tcb)
 {
-  /* Return true if the PID hashes to this TCB. */
+  /* Return true if the PID hashes to this TCB.  This will catch the case
+   * where the task associated with the TCB has terminated (note that
+   * sched_releasedtcb() will nullify the TCB field in that case).  The
+   * following logic will also detect the case where the task assocated
+   * with the TCB has terminated and another task has been started with a
+   * different TCB but with a PID hashing to the same entry.
+   *
+   * NOTE: In the event that the TCB has terminated, the 'tcb' parameter
+   * will point at either a stale or a re-allocated memory allocation.  The
+   * PID fetched by the use of the bad pointer(tcb->pid) should not cause
+   * any memory faults (at least in the FLAT or PROTECTED builds) because
+   * we do at least know that the pointer refers to valid memory and the
+   * hash macro, PIDHASH(), will return a valid, in-range index into the
+   * g_pidhash[] table.
+   *
+   * REVISIT:  This logic will not, however, catch the case where the task
+   * originally associated with the TCB has terminated, but a new task was
+   * started reusing the same memory allocation for its TDB that was freed
+   * by the terminated task.  In this case, a false positive value will be
+   * returned:  The TCB is valid but does not refer to the same task as
+   * before.  This case is not detectable with the limited amount of
+   * information available.
+   */
 
   return tcb == g_pidhash[PIDHASH(tcb->pid)].tcb;
 }
-