diff --git a/lib_xua/api/xua_endpoint0.h b/lib_xua/api/xua_endpoint0.h
index bbce8166..05d56d6d 100644
--- a/lib_xua/api/xua_endpoint0.h
+++ b/lib_xua/api/xua_endpoint0.h
@@ -15,7 +15,10 @@
  *  \param c_ep0_out Chanend connected to the XUD_Manager() out endpoint array
  *  \param c_ep0_in Chanend connected to the XUD_Manager() in endpoint array
  *  \param c_audioCtrl Chanend connected to the decouple thread for control
- *                     audio (sample rate changes etc.)
+ *                     audio (sample rate changes etc.). Note when nulled, the
+ *                    audio device only supports single sample rate/format and
+ *                    DFU is not supported either since this channel is used
+ *                    to carry messages about format, rate and DFU state
  *  \param c_mix_ctl Optional chanend to be connected to the mixer thread if
  *                   present
  *  \param c_clk_ctl Optional chanend to be connected to the clockgen thread if