diff --git a/radio/src/gui/128x64/radio_version.cpp b/radio/src/gui/128x64/radio_version.cpp
index 7334ed96b..387ccb99f 100644
--- a/radio/src/gui/128x64/radio_version.cpp
+++ b/radio/src/gui/128x64/radio_version.cpp
@@ -32,8 +32,9 @@ void menuRadioVersion(event_t event)
 #endif
   
 #if defined(STM32)
+  char id[27];
   if (event == EVT_ENTRY) {
-    getCPUUniqueID(reusableBuffer.version.id);
+    getCPUUniqueID(id);
   }
 #endif
   
diff --git a/radio/src/gui/212x64/radio_version.cpp b/radio/src/gui/212x64/radio_version.cpp
index c06e52372..7eb6b5ebf 100644
--- a/radio/src/gui/212x64/radio_version.cpp
+++ b/radio/src/gui/212x64/radio_version.cpp
@@ -22,6 +22,7 @@
 
 void menuRadioVersion(event_t event)
 {
+  char id[27];
   if (warningResult) {
     warningResult = 0;
     showMessageBox(STR_STORAGE_FORMAT);
@@ -30,14 +31,14 @@ void menuRadioVersion(event_t event)
   }
 
   if (event == EVT_ENTRY) {
-    getCPUUniqueID(reusableBuffer.version.id);
+    getCPUUniqueID(id);
   }
   
   SIMPLE_MENU(STR_MENUVERSION, menuTabGeneral, MENU_RADIO_VERSION, 1);
 
   lcdDrawTextAlignedLeft(MENU_HEADER_HEIGHT+1, vers_stamp);
   lcdDrawTextAlignedLeft(MENU_HEADER_HEIGHT+4*FH+1, "UID\037\033:");
-  lcdDrawText(5*FW+3, MENU_HEADER_HEIGHT+4*FH+1, reusableBuffer.version.id);
+  lcdDrawText(5*FW+3, MENU_HEADER_HEIGHT+4*FH+1, id);
 
   lcdDrawTextAlignedLeft(MENU_HEADER_HEIGHT+5*FH+1, STR_EEBACKUP);
   lcdDrawTextAlignedLeft(MENU_HEADER_HEIGHT+6*FH+1, STR_FACTORYRESET);
diff --git a/radio/src/gui/480x272/radio_version.cpp b/radio/src/gui/480x272/radio_version.cpp
index 2af42c988..e441a446b 100644
--- a/radio/src/gui/480x272/radio_version.cpp
+++ b/radio/src/gui/480x272/radio_version.cpp
@@ -22,6 +22,7 @@
 
 bool menuRadioVersion(event_t event)
 {
+  char id[27];
 #if 0
   if (warningResult) {
     warningResult = 0;
@@ -32,7 +33,7 @@ bool menuRadioVersion(event_t event)
 #endif
 
   if (event == EVT_ENTRY) {
-    getCPUUniqueID(reusableBuffer.version.id);
+    getCPUUniqueID(id);
   }
 
   SIMPLE_MENU(STR_MENUVERSION, RADIO_ICONS, menuTabGeneral, MENU_RADIO_VERSION, 0);
@@ -42,7 +43,7 @@ bool menuRadioVersion(event_t event)
   lcdDrawText(MENUS_MARGIN_LEFT, MENU_CONTENT_TOP + 3*FH, time_stamp);
   lcdDrawText(MENUS_MARGIN_LEFT, MENU_CONTENT_TOP + 4*FH, eeprom_stamp);
   lcdDrawText(MENUS_MARGIN_LEFT, MENU_CONTENT_TOP + 5*FH, "UID:");
-  lcdDrawText(MENUS_MARGIN_LEFT + 64, MENU_CONTENT_TOP + 5*FH, reusableBuffer.version.id);
+  lcdDrawText(MENUS_MARGIN_LEFT + 64, MENU_CONTENT_TOP + 5*FH, id);
 
 #if 0
   if (event == EVT_KEY_LONG(KEY_ENTER)) {
diff --git a/radio/src/main_arm.cpp b/radio/src/main_arm.cpp
index 49476aa82..bc59d620e 100644
--- a/radio/src/main_arm.cpp
+++ b/radio/src/main_arm.cpp
@@ -58,7 +58,7 @@ void handleUsbConnection()
 #endif
       POPUP_MENU_START(onUSBConnectMenu);
     }
-    if (g_eeGeneral.USBMode != USB_UNSELECTED_MODE) {
+    if (g_eeGeneral.USBMode != USB_UNSELECTED_MODE && g_eeGeneral.USBMode <= USB_MAX_MODE) {
       setSelectedUsbMode(g_eeGeneral.USBMode);
     }
   }
diff --git a/radio/src/mixer.cpp b/radio/src/mixer.cpp
index a6d22568d..5c8695517 100644
--- a/radio/src/mixer.cpp
+++ b/radio/src/mixer.cpp
@@ -1089,7 +1089,6 @@ void evalFlightModeMixes(uint8_t mode, uint8_t tick10ms)
   mixWarning = lv_mixWarning;
 }
 
-int32_t sum_chans512[MAX_OUTPUT_CHANNELS] = {0};
 
 
 #define MAX_ACT 0xffff
@@ -1102,6 +1101,7 @@ uint8_t   flightModeTransitionLast = 255;
 
 void evalMixes(uint8_t tick10ms)
 {
+  int32_t sum_chans512[MAX_OUTPUT_CHANNELS] = {0};
 #if defined(PCBMEGA2560) && defined(DEBUG) && !defined(VOICE)
   PORTH |= 0x40; // PORTH:6 LOW->HIGH signals start of mixer interrupt
 #endif
diff --git a/radio/src/opentx.cpp b/radio/src/opentx.cpp
index 3dd40b2fc..1c3481ef0 100644
--- a/radio/src/opentx.cpp
+++ b/radio/src/opentx.cpp
@@ -49,7 +49,12 @@ uint8_t heartbeat;
 safetych_t safetyCh[MAX_OUTPUT_CHANNELS];
 #endif
 
-union ReusableBuffer reusableBuffer;
+// __DMA for the MSC_BOT_Data member
+union ReusableBuffer reusableBuffer __DMA;
+
+#if defined(STM32)
+uint8_t* MSC_BOT_Data = reusableBuffer.MSC_BOT_Data;
+#endif
 
 const pm_uint8_t bchout_ar[] PROGMEM = {
     0x1B, 0x1E, 0x27, 0x2D, 0x36, 0x39,
diff --git a/radio/src/opentx.h b/radio/src/opentx.h
index 24d02f8b8..5d983a6a3 100644
--- a/radio/src/opentx.h
+++ b/radio/src/opentx.h
@@ -27,6 +27,9 @@
 #include <stdlib.h>
 #include "definitions.h"
 #include "opentx_types.h"
+#if defined(STM32)
+#include "usbd_conf.h"
+#endif
 
 #if defined(SIMU)
   #define SWITCH_SIMU(a, b)  (a)
@@ -1495,16 +1498,15 @@ union ReusableBuffer
   } sdmanager;
 #endif
 
-#if defined(STM32)
-  struct
-  {
-    char id[27];
-  } version;
-#endif
   struct
   {
     uint8_t stickMode;
   } generalSettings;
+
+#if defined(STM32)
+  // Data for the USB mass storage driver. If USB mass storage runs no menu is not allowed to be displayed
+  uint8_t MSC_BOT_Data[MSC_MEDIA_PACKET];
+#endif
 };
 
 extern union ReusableBuffer reusableBuffer;
diff --git a/radio/src/serial.cpp b/radio/src/serial.cpp
index 1fa789765..dc49c2d10 100644
--- a/radio/src/serial.cpp
+++ b/radio/src/serial.cpp
@@ -26,7 +26,7 @@
 #define PRINTF_BUFFER_SIZE    128
 
 void serialPutc(char c) {
-#if !defined(BOOT)
+#if !defined(BOOT) && defined(USB_SERIAL)
   if (getSelectedUsbMode() == USB_SERIAL_MODE)
     usbSerialPutc(c);
 #endif
diff --git a/radio/src/targets/common/arm/stm32/CMakeLists.txt b/radio/src/targets/common/arm/stm32/CMakeLists.txt
index 2db6d0ed4..78917813d 100644
--- a/radio/src/targets/common/arm/stm32/CMakeLists.txt
+++ b/radio/src/targets/common/arm/stm32/CMakeLists.txt
@@ -38,14 +38,18 @@ set(FIRMWARE_TARGET_SRC
   ../common/arm/stm32/usb_driver.cpp
   ../common/arm/stm32/flash_driver.cpp
   )
-set(FIRMWARE_TARGET_SRC
-  ${FIRMWARE_TARGET_SRC}
-  ../common/arm/stm32/usbd_cdc.cpp
+
+if(DEBUG)
+  set(STM32USB_SRC
+    ${STM32USB_SRC}
+    STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c
   )
-set(STM32USB_SRC
-  ${STM32USB_SRC}
-  STM32_USB_Device_Library/Class/cdc/src/usbd_cdc_core.c
+  set(FIRMWARE_TARGET_SRC
+    ${FIRMWARE_TARGET_SRC}
+    ../common/arm/stm32/usbd_cdc.cpp
   )
+  add_definitions(-DUSB_SERIAL)
+endif()
 set(STM32USB_SRC
   ${STM32USB_SRC}
   STM32_USB_Device_Library/Class/msc/src/usbd_msc_data.c
diff --git a/radio/src/targets/common/arm/stm32/bootloader/CMakeLists.txt b/radio/src/targets/common/arm/stm32/bootloader/CMakeLists.txt
index 3e88f4296..48f15d29f 100644
--- a/radio/src/targets/common/arm/stm32/bootloader/CMakeLists.txt
+++ b/radio/src/targets/common/arm/stm32/bootloader/CMakeLists.txt
@@ -109,6 +109,7 @@ endif()
 remove_definitions(-DDISK_CACHE)
 remove_definitions(-DLUA)
 remove_definitions(-DCLI)
+remove_definitions(-DUSB_SERIAL)
 add_definitions(-DBOOT)
 
 set(CMAKE_EXE_LINKER_FLAGS "-mcpu=${MCU} -mthumb -nostartfiles -lm -T${RADIO_SRC_DIRECTORY}/targets/${TARGET_DIR}/stm32_ramboot.ld -Wl,-Map=bootloader.map,--cref,--no-warn-mismatch,--gc-sections")
diff --git a/radio/src/targets/common/arm/stm32/usb_driver.cpp b/radio/src/targets/common/arm/stm32/usb_driver.cpp
index 946da0414..7e31ce5d0 100644
--- a/radio/src/targets/common/arm/stm32/usb_driver.cpp
+++ b/radio/src/targets/common/arm/stm32/usb_driver.cpp
@@ -91,6 +91,8 @@ void usbStart()
       // initialize USB as HID device
       USBD_Init(&USB_OTG_dev, USB_OTG_FS_CORE_ID, &USR_desc, &USBD_HID_cb, &USR_cb);
       break;
+#endif
+#if defined(USB_SERIAL)
     case USB_SERIAL_MODE:
       // initialize USB as CDC device (virtual serial port)
       USBD_Init(&USB_OTG_dev, USB_OTG_FS_CORE_ID, &USR_desc, &USBD_CDC_cb, &USR_cb);
diff --git a/radio/src/targets/common/arm/stm32/usb_driver.h b/radio/src/targets/common/arm/stm32/usb_driver.h
index 2d26fa930..90e1ccd84 100644
--- a/radio/src/targets/common/arm/stm32/usb_driver.h
+++ b/radio/src/targets/common/arm/stm32/usb_driver.h
@@ -27,7 +27,7 @@ enum usbMode {
   USB_JOYSTICK_MODE,
   USB_MASS_STORAGE_MODE,
   USB_SERIAL_MODE,
-#if defined(DEBUG)
+#if defined(USB_SERIAL)
   USB_MAX_MODE=USB_SERIAL_MODE
 #else
   USB_MAX_MODE=USB_MASS_STORAGE_MODE
diff --git a/radio/src/targets/common/arm/stm32/usbd_conf.h b/radio/src/targets/common/arm/stm32/usbd_conf.h
index 7feff433f..594d061f1 100644
--- a/radio/src/targets/common/arm/stm32/usbd_conf.h
+++ b/radio/src/targets/common/arm/stm32/usbd_conf.h
@@ -23,7 +23,7 @@
 #define _USBD_CONF_H_
 
 /* Includes ------------------------------------------------------------------*/
-#include "usb_conf.h"
+#include <inttypes.h>
 
 #define USBD_CFG_MAX_NUM           1
 #define USBD_ITF_MAX_NUM           1
@@ -37,7 +37,12 @@
 #define MSC_OUT_EP                   0x01
 #define MSC_MAX_PACKET               64
 
+// Save some RAM on smaller STM32 processors. Slightly lowers USB mass storage speed
+#if defined(STM32F2) && !defined(BOOT)
+#define MSC_MEDIA_PACKET             512
+#else
 #define MSC_MEDIA_PACKET             4096
+#endif
 
 #define HID_IN_EP                    0x81
 #define HID_OUT_EP                   0x01
diff --git a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/inc/usbd_msc_bot.h b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/inc/usbd_msc_bot.h
index cf960ad4f..e8e8c99ab 100644
--- a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/inc/usbd_msc_bot.h
+++ b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/inc/usbd_msc_bot.h
@@ -27,6 +27,7 @@
 
 /* Define to prevent recursive inclusion -------------------------------------*/
 
+#include "usb_conf.h"
 #include "usbd_core.h"
 
 /* Define to prevent recursive inclusion -------------------------------------*/
@@ -111,7 +112,11 @@ MSC_BOT_CSW_TypeDef;
   * @{
   */
 
+#if defined(BOOT)
 extern uint8_t              MSC_BOT_Data[];
+#else
+extern uint8_t*              MSC_BOT_Data;
+#endif
 extern uint16_t             MSC_BOT_DataLen;
 extern uint8_t              MSC_BOT_State;
 extern uint8_t              MSC_BOT_BurstMode;
diff --git a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/src/usbd_msc_bot.c b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/src/usbd_msc_bot.c
index 5aff1a9c4..e1e9a2536 100644
--- a/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/src/usbd_msc_bot.c
+++ b/radio/src/thirdparty/STM32_USB-Host-Device_Lib_V2.2.0/Libraries/STM32_USB_Device_Library/Class/msc/src/usbd_msc_bot.c
@@ -80,7 +80,9 @@ uint8_t              MSC_BOT_Status;
 #endif /* USB_OTG_HS_INTERNAL_DMA_ENABLED */
 
 #include "definitions.h"
-uint8_t              MSC_BOT_Data[MSC_MEDIA_PACKET] __DMA;	// modified by OpenTX
+#if defined(BOOT)
+uint8_t  MSC_BOT_Data[MSC_MEDIA_PACKET] __DMA;	// modified by OpenTX
+#endif
 
 #ifdef USB_OTG_HS_INTERNAL_DMA_ENABLED
   #if defined ( __ICCARM__ ) /*!< IAR Compiler */