diff --git a/Makefile b/Makefile
index dbf7528..4318bd9 100644
--- a/Makefile
+++ b/Makefile
@@ -17,8 +17,8 @@ ST_LIB = stm32_lib
 ST_USB = usb_lib
 
 # Optimization level [0,1,2,3,s]
-OPT = 0
-DEBUG = -g
+OPT ?= 0
+DEBUG = 
 #DEBUG = dwarf-2
 
 INCDIRS = ./$(ST_LIB) ./$(ST_USB)
diff --git a/dfu.c b/dfu.c
index ab0cac9..a5ec00b 100644
--- a/dfu.c
+++ b/dfu.c
@@ -35,19 +35,19 @@
 #include "usb.h"
 
 /* DFU globals */
-u32 userAppAddr = USER_CODE_RAM; /* default RAM user code location */
-u32 userAppEnd = RAM_END;
-DFUStatus dfuAppStatus;       /* includes state */
-bool userFlash = FALSE;
-bool dfuBusy = FALSE;
+static volatile u32 userAppAddr = USER_CODE_RAM; /* default RAM user code location */
+static volatile u32 userAppEnd = RAM_END;
+static volatile DFUStatus dfuAppStatus;       /* includes state */
+static volatile bool userFlash = FALSE;
+volatile bool dfuBusy = FALSE;
 
-u8 recvBuffer[wTransferSize];
-u32 userFirmwareLen = 0;
-u16 thisBlockLen = 0;
-u16 uploadBlockLen = 0;
+static volatile u8 recvBuffer[wTransferSize] __attribute__((aligned(4)));
+static volatile u32 userFirmwareLen = 0;
+static volatile u16 thisBlockLen = 0;
+static volatile u16 uploadBlockLen = 0;
 
 
-PLOT code_copy_lock;
+volatile PLOT code_copy_lock;
 
 /* todo: force dfu globals to be singleton to avoid re-inits? */
 void dfuInit(void) {
@@ -330,7 +330,7 @@ u8 *dfuCopyStatus(u16 length) {
         pInformation->Ctrl_Info.Usb_wLength = 6;
         return NULL;
     } else {
-        return(&dfuAppStatus);
+        return (u8*)(&dfuAppStatus);
     }
 }
 
@@ -371,7 +371,7 @@ void dfuCopyBufferToExec() {
         flashErasePage((u32)(userSpace));
 
         for (i = 0; i < thisBlockLen; i = i + 4) {
-            flashWriteWord(userSpace++, *(u32 *)(recvBuffer + i));
+            flashWriteWord((u32)(userSpace++), *(u32 *)(recvBuffer +i));
         }
 
     }
diff --git a/dfu.h b/dfu.h
index b9b9c95..4ebd0b3 100644
--- a/dfu.h
+++ b/dfu.h
@@ -93,7 +93,7 @@ typedef enum _PLOT {
 
 
 
-extern bool dfuBusy;
+extern volatile bool dfuBusy;
 
 /* exposed functions */
 void dfuInit(void);  /* singleton dfu initializer */