diff --git a/libraries/AP_HAL_FLYMAPLE/FlymaplePortingNotes.txt b/libraries/AP_HAL_FLYMAPLE/FlymaplePortingNotes.txt
index dc8ec860c6..1ac110f832 100644
--- a/libraries/AP_HAL_FLYMAPLE/FlymaplePortingNotes.txt
+++ b/libraries/AP_HAL_FLYMAPLE/FlymaplePortingNotes.txt
@@ -110,6 +110,29 @@ LIBMAPLE_PATH = $(HOME)/libmaple
 # Also, the ARM compiler tools MUST be in your current PATH
 #config.mk END
 
+Interrupt disabling on ARM
+
+On AVR, ISRs run by default with the global interrupt enable flag disabled, 
+whereas mainline code runs by default with global interrupt enable flag 
+*enabled*. Which means that cli()/sei() in an ISR will have a different effect 
+to cli()sei() in mainline code. Thats why code that *might* run in an ISR must 
+use the special idiom: so that it restores the flag to the state it was before 
+the critical block
+
+On ARM, the global interrupt disable flag PRIMASK is not altered behind your 
+back by hardware. By default its always clear (ie enabled) even in ISRs. A 
+different mechanism prevents ISRs from being reinterrupted. This means that 
+non-nested noInterrupts()/interrupts() will always leave the PRIMASK as it was 
+(interrupts enabled) when the critical block started, whether in ISRs or 
+mainline code.
+
+Conclusion:
+
+On AVR, cli()/sei() is dangerous both in ISRs *and* when nested.
+
+On ARM, noInterrupts()/interrupts() is only dangerous when nested.
+
+
 Remaining issues:
 
 1. For reasons I do not yet understand, the magnetic heading reported by
diff --git a/libraries/AP_HAL_FLYMAPLE/Scheduler.cpp b/libraries/AP_HAL_FLYMAPLE/Scheduler.cpp
index 056db34c73..d4e4f40c61 100644
--- a/libraries/AP_HAL_FLYMAPLE/Scheduler.cpp
+++ b/libraries/AP_HAL_FLYMAPLE/Scheduler.cpp
@@ -1,30 +1,17 @@
-/*
-   This program is free software: you can redistribute it and/or modify
-   it under the terms of the GNU General Public License as published by
-   the Free Software Foundation, either version 3 of the License, or
-   (at your option) any later version.
-
-   This program is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-   GNU General Public License for more details.
-
-   You should have received a copy of the GNU General Public License
-   along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-/*
-  Flymaple port by Mike McCauley
- */
-#include <AP_HAL.h>
-
-#if CONFIG_HAL_BOARD == HAL_BOARD_FLYMAPLE
-
 // Scheduler.cpp
 //
 // Flymaple Scheduler.
 // We use systick interrupt for the 1kHz ordinary timers.
 // We use a slightly higher priority HardwareTimer 2 for the failsafe callbacks
 // so a hung timer wont prevent the failsafe timer interrupt running
+//
+// Use of noInterrupts()/interrupts() on FLymaple ARM processor.
+// Please see the notes in FlymaplePortingNotes.txt in this directory for 
+// information about disabling interrupts on Flymaple
+
+#include <AP_HAL.h>
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_FLYMAPLE
 
 #include "Scheduler.h"