diff --git a/libraries/DataFlash/DataFlash_APM1.cpp b/libraries/DataFlash/DataFlash_APM1.cpp
index 916b4c31b0..1fa271e8e2 100644
--- a/libraries/DataFlash/DataFlash_APM1.cpp
+++ b/libraries/DataFlash/DataFlash_APM1.cpp
@@ -64,6 +64,16 @@ extern const AP_HAL::HAL& hal;
 #define DF_CHIP_ERASE_2   0x80
 #define DF_CHIP_ERASE_3   0x9A
 
+/*
+  try to take a semaphore safely from both in a timer and outside
+ */
+bool DataFlash_APM1::_sem_take(uint8_t timeout)
+{
+    if (hal.scheduler->in_timerprocess()) {
+        return _spi_sem->take_nonblocking();
+    }
+    return _spi_sem->take(timeout);
+}
 
 
 // Public Methods //////////////////////////////////////////////////////////////
@@ -102,7 +112,7 @@ void DataFlash_APM1::Init(void)
 // This function is mainly to test the device
 void DataFlash_APM1::ReadManufacturerID()
 {
-    if (!_spi_sem->take(5))
+    if (!_sem_take(5))
         return;
     // activate dataflash command decoder
     _spi->cs_assert();
@@ -157,7 +167,7 @@ uint8_t DataFlash_APM1::ReadStatus()
 inline
 uint16_t DataFlash_APM1::PageSize()
 {
-    if (!_spi_sem->take(5))
+    if (!_sem_take(5))
         return 0;
     
     uint16_t ret = 528-((ReadStatusReg()&0x01) << 4); // if first bit 1 trhen 512 else 528 bytes
@@ -175,7 +185,7 @@ void DataFlash_APM1::WaitReady()
 
 void DataFlash_APM1::PageToBuffer(uint8_t BufferNum, uint16_t PageAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
 
     // activate dataflash command decoder
@@ -202,7 +212,7 @@ void DataFlash_APM1::PageToBuffer(uint8_t BufferNum, uint16_t PageAdr)
 
 void DataFlash_APM1::BufferToPage (uint8_t BufferNum, uint16_t PageAdr, uint8_t wait)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
 
     // activate dataflash command decoder
@@ -234,7 +244,7 @@ void DataFlash_APM1::BlockWrite (uint8_t BufferNum, uint16_t IntPageAdr,
                                  const void *pHeader, uint8_t hdr_size,
                                  const void *pBuffer, uint16_t size)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     
     // activate dataflash command decoder
@@ -262,7 +272,7 @@ void DataFlash_APM1::BlockWrite (uint8_t BufferNum, uint16_t IntPageAdr,
 
 bool DataFlash_APM1::BlockRead(uint8_t BufferNum, uint16_t IntPageAdr, void *pBuffer, uint16_t size)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return false;
 
     // activate dataflash command decoder
@@ -292,7 +302,7 @@ bool DataFlash_APM1::BlockRead(uint8_t BufferNum, uint16_t IntPageAdr, void *pBu
 
 void DataFlash_APM1::PageErase (uint16_t PageAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
 
     // activate dataflash command decoder
@@ -320,7 +330,7 @@ void DataFlash_APM1::PageErase (uint16_t PageAdr)
 
 void DataFlash_APM1::BlockErase (uint16_t BlockAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
 
     // activate dataflash command decoder
@@ -358,7 +368,7 @@ void DataFlash_APM1::BlockErase (uint16_t BlockAdr)
 
 void DataFlash_APM1::ChipErase()
 {
-    if (!_spi_sem->take(5))
+    if (!_sem_take(5))
         return;
 
     // activate dataflash command decoder
diff --git a/libraries/DataFlash/DataFlash_APM1.h b/libraries/DataFlash/DataFlash_APM1.h
index fbb2d377a0..8057d2fc49 100644
--- a/libraries/DataFlash/DataFlash_APM1.h
+++ b/libraries/DataFlash/DataFlash_APM1.h
@@ -40,6 +40,9 @@ private:
     AP_HAL::SPIDeviceDriver *_spi;
     AP_HAL::Semaphore *_spi_sem;
 
+    // take a semaphore safely
+    bool		            _sem_take(uint8_t timeout);
+
 public:
     void        Init();
     void        ReadManufacturerID();
diff --git a/libraries/DataFlash/DataFlash_APM2.cpp b/libraries/DataFlash/DataFlash_APM2.cpp
index ea3aaebf2b..dfa2daf8ee 100644
--- a/libraries/DataFlash/DataFlash_APM2.cpp
+++ b/libraries/DataFlash/DataFlash_APM2.cpp
@@ -64,6 +64,17 @@ extern const AP_HAL::HAL& hal;
 #define DF_CHIP_ERASE_3   0x9A
 
 
+/*
+  try to take a semaphore safely from both in a timer and outside
+ */
+bool DataFlash_APM2::_sem_take(uint8_t timeout)
+{
+    if (hal.scheduler->in_timerprocess()) {
+        return _spi_sem->take_nonblocking();
+    }
+    return _spi_sem->take(timeout);
+}
+
 
 // Public Methods //////////////////////////////////////////////////////////////
 void DataFlash_APM2::Init(void)
@@ -92,7 +103,7 @@ void DataFlash_APM2::Init(void)
         return; /* never reached */
     }
 
-    if (!_spi_sem->take(5))
+    if (!_sem_take(5))
         return;
     // get page size: 512 or 528  (by default: 528)
     df_PageSize=PageSize();
@@ -182,7 +193,7 @@ void DataFlash_APM2::WaitReady()
 
 void DataFlash_APM2::PageToBuffer(uint8_t BufferNum, uint16_t PageAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
 
     // activate dataflash command decoder
@@ -213,7 +224,7 @@ void DataFlash_APM2::PageToBuffer(uint8_t BufferNum, uint16_t PageAdr)
 
 void DataFlash_APM2::BufferToPage (uint8_t BufferNum, uint16_t PageAdr, uint8_t wait)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     // activate dataflash command decoder
     _spi->cs_assert();
@@ -245,7 +256,7 @@ void DataFlash_APM2::BlockWrite (uint8_t BufferNum, uint16_t IntPageAdr,
                                  const void *pHeader, uint8_t hdr_size,
                                  const void *pBuffer, uint16_t size)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     // activate dataflash command decoder
     _spi->cs_assert();
@@ -273,7 +284,7 @@ void DataFlash_APM2::BlockWrite (uint8_t BufferNum, uint16_t IntPageAdr,
 
 bool DataFlash_APM2::BlockRead(uint8_t BufferNum, uint16_t IntPageAdr, void *pBuffer, uint16_t size)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return false;
 
     // activate dataflash command decoder
@@ -315,7 +326,7 @@ uint8_t DataFlash_APM2::BufferRead (uint8_t BufferNum, uint16_t IntPageAdr)
 
 void DataFlash_APM2::PageErase (uint16_t PageAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     // activate dataflash command decoder
     _spi->cs_assert();
@@ -344,7 +355,7 @@ void DataFlash_APM2::PageErase (uint16_t PageAdr)
 // erase a block of 8 pages.
 void DataFlash_APM2::BlockErase(uint16_t BlockAdr)
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     // activate dataflash command decoder
     _spi->cs_assert();
@@ -373,7 +384,7 @@ void DataFlash_APM2::BlockErase(uint16_t BlockAdr)
 
 void DataFlash_APM2::ChipErase()
 {
-    if (!_spi_sem->take(1))
+    if (!_sem_take(1))
         return;
     //serialDebug("Chip Erase\n");
 
diff --git a/libraries/DataFlash/DataFlash_APM2.h b/libraries/DataFlash/DataFlash_APM2.h
index 6cce57cedb..e6fa6c6daf 100644
--- a/libraries/DataFlash/DataFlash_APM2.h
+++ b/libraries/DataFlash/DataFlash_APM2.h
@@ -38,6 +38,9 @@ private:
     void                    BlockErase (uint16_t BlockAdr);
     void                    ChipErase();
 
+    // take a semaphore safely
+    bool		            _sem_take(uint8_t timeout);
+
     AP_HAL::SPIDeviceDriver* _spi;
     AP_HAL::Semaphore* _spi_sem;