diff --git a/examples/device/nrf52840/segger/nrf52840.emProject b/examples/device/nrf52840/segger/nrf52840.emProject
index 8775d1bc..5851c33d 100644
--- a/examples/device/nrf52840/segger/nrf52840.emProject
+++ b/examples/device/nrf52840/segger/nrf52840.emProject
@@ -32,12 +32,6 @@
       target_reset_script="Reset();"
       target_script_file="$(ProjectDir)/nRF_Target.js"
       target_trace_initialize_script="EnableTrace("$(TraceInterfaceType)")" />
-    <folder Name="RTT Files">
-      <file file_name="SEGGER_RTT.c" />
-      <file file_name="SEGGER_RTT.h" />
-      <file file_name="SEGGER_RTT_Conf.h" />
-      <file file_name="SEGGER_RTT_SES.c" />
-    </folder>
     <folder Name="Script Files">
       <file file_name="nRF_Target.js">
         <configuration Name="Common" file_type="Reset Script" />
@@ -61,6 +55,12 @@
       <file file_name="../src/msc_app.h" />
       <file file_name="../src/msc_flash_ram.c" />
       <file file_name="../src/msc_flash_qspi.c" />
+      <folder Name="segger_rtt">
+        <file file_name="../src/segger_rtt/SEGGER_RTT.c" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT_Conf.h" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT.h" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT_SES.c" />
+      </folder>
     </folder>
     <folder Name="hw">
       <folder Name="bsp">
diff --git a/examples/device/nrf52840/src/main.c b/examples/device/nrf52840/src/main.c
index 58ac1ad2..11b73ebf 100644
--- a/examples/device/nrf52840/src/main.c
+++ b/examples/device/nrf52840/src/main.c
@@ -55,56 +55,51 @@
 //--------------------------------------------------------------------+
 void print_greeting(void);
 void led_blinking_task(void);
-void virtual_com_task(void);
-void usb_hid_task(void);
-
-/*------------- MAIN -------------*/
-int main(void)
-{
-  board_init();
-  print_greeting();
-
-  tusb_init();
-
-  while (1)
-  {
-    tusb_task();
-
-    led_blinking_task();
-    virtual_com_task();
-
-    usb_hid_task();
-  }
-
-  return 0;
-}
 
 //--------------------------------------------------------------------+
 // USB CDC
 //--------------------------------------------------------------------+
+#if CFG_TUD_CDC
 void virtual_com_task(void)
 {
-#if CFG_TUD_CDC
   // connected and there are data available
-  if ( tud_mounted() && tud_cdc_available() )
+  if ( tud_cdc_connected() )
   {
-    uint8_t buf[64];
+    if ( tud_cdc_available() )
+    {
+      uint8_t buf[64];
 
-    // read and echo back
-    uint32_t count = tud_cdc_read(buf, sizeof(buf));
+      // read and echo back
+      uint32_t count = tud_cdc_read(buf, sizeof(buf));
+
+      tud_cdc_write(buf, count);
+    }
 
-    tud_cdc_write(buf, count);
     tud_cdc_write_flush();
   }
-#endif
 }
 
+void tud_cdc_line_state_cb(uint8_t itf, bool dtr, bool rts)
+{
+  (void) itf;
+
+  // connected
+  if ( dtr && rts )
+  {
+    // print greeting
+    tud_cdc_write_str("tinyusb usb cdc\n");
+  }
+}
+#else
+#define virtual_com_task()
+#endif
+
 //--------------------------------------------------------------------+
 // USB HID
 //--------------------------------------------------------------------+
+#if CFG_TUD_HID
 void usb_hid_task(void)
 {
-#if CFG_TUD_HID
   // Poll every 10ms
   static tu_timeout_t tm = { .start = 0, .interval = 10 };
 
@@ -144,10 +139,8 @@ void usb_hid_task(void)
     if ( btn & 0x04 ) tud_hid_mouse_move(  0   , -DELTA); // up
     if ( btn & 0x08 ) tud_hid_mouse_move(  0   ,  DELTA); // down
   }
-#endif
 }
 
-#if CFG_TUD_HID
 uint16_t tud_hid_generic_get_report_cb(uint8_t report_id, hid_report_type_t report_type, uint8_t* buffer, uint16_t reqlen)
 {
   // TODO not Implemented
@@ -158,8 +151,32 @@ void tud_hid_generic_set_report_cb(uint8_t report_id, hid_report_type_t report_t
 {
   // TODO not Implemented
 }
+
+#else
+#define usb_hid_task()
 #endif
 
+
+/*------------- MAIN -------------*/
+int main(void)
+{
+  board_init();
+  print_greeting();
+
+  tusb_init();
+
+  while (1)
+  {
+    tusb_task();
+
+    led_blinking_task();
+    virtual_com_task();
+    usb_hid_task();
+  }
+
+  return 0;
+}
+
 //--------------------------------------------------------------------+
 // tinyusb callbacks
 //--------------------------------------------------------------------+
diff --git a/examples/device/nrf52840/segger/SEGGER_RTT.c b/examples/device/nrf52840/src/segger_rtt/SEGGER_RTT.c
similarity index 100%
rename from examples/device/nrf52840/segger/SEGGER_RTT.c
rename to examples/device/nrf52840/src/segger_rtt/SEGGER_RTT.c
diff --git a/examples/device/nrf52840/segger/SEGGER_RTT.h b/examples/device/nrf52840/src/segger_rtt/SEGGER_RTT.h
similarity index 100%
rename from examples/device/nrf52840/segger/SEGGER_RTT.h
rename to examples/device/nrf52840/src/segger_rtt/SEGGER_RTT.h
diff --git a/examples/device/nrf52840/segger/SEGGER_RTT_Conf.h b/examples/device/nrf52840/src/segger_rtt/SEGGER_RTT_Conf.h
similarity index 100%
rename from examples/device/nrf52840/segger/SEGGER_RTT_Conf.h
rename to examples/device/nrf52840/src/segger_rtt/SEGGER_RTT_Conf.h
diff --git a/examples/device/nrf52840/segger/SEGGER_RTT_SES.c b/examples/device/nrf52840/src/segger_rtt/SEGGER_RTT_SES.c
similarity index 100%
rename from examples/device/nrf52840/segger/SEGGER_RTT_SES.c
rename to examples/device/nrf52840/src/segger_rtt/SEGGER_RTT_SES.c
diff --git a/examples/device/nrf52840_freertos/segger/nrf5x_freertos.emProject b/examples/device/nrf52840_freertos/segger/nrf5x_freertos.emProject
index f01207ba..661dc12a 100644
--- a/examples/device/nrf52840_freertos/segger/nrf5x_freertos.emProject
+++ b/examples/device/nrf52840_freertos/segger/nrf5x_freertos.emProject
@@ -32,12 +32,6 @@
       target_reset_script="Reset();"
       target_script_file="$(ProjectDir)/nRF_Target.js"
       target_trace_initialize_script="EnableTrace(&quot;$(TraceInterfaceType)&quot;)" />
-    <folder Name="RTT Files">
-      <file file_name="SEGGER_RTT.c" />
-      <file file_name="SEGGER_RTT.h" />
-      <file file_name="SEGGER_RTT_Conf.h" />
-      <file file_name="SEGGER_RTT_SES.c" />
-    </folder>
     <folder Name="Script Files">
       <file file_name="nRF_Target.js">
         <configuration Name="Common" file_type="Reset Script" />
@@ -60,6 +54,12 @@
       <file file_name="../src/msc_flash_qspi.c" />
       <file file_name="../src/msc_app.c" />
       <file file_name="../src/msc_app.h" />
+      <folder Name="segger_rtt">
+        <file file_name="../src/segger_rtt/SEGGER_RTT.c" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT_Conf.h" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT.h" />
+        <file file_name="../src/segger_rtt/SEGGER_RTT_SES.c" />
+      </folder>
     </folder>
     <folder Name="hw">
       <folder Name="bsp">
diff --git a/examples/device/nrf52840_freertos/src/main.c b/examples/device/nrf52840_freertos/src/main.c
index 6fb76a84..d5a5d0c2 100644
--- a/examples/device/nrf52840_freertos/src/main.c
+++ b/examples/device/nrf52840_freertos/src/main.c
@@ -101,18 +101,32 @@ void cdc_task(void* params)
   while ( 1 )
   {
     // connected and there are data available
-    if ( tud_mounted() && tud_cdc_available() )
+    if ( tud_cdc_connected() )
     {
-      uint8_t buf[64];
+      if ( tud_cdc_available() )
+      {
+        uint8_t buf[64];
 
-      // read and echo back
-      uint32_t count = tud_cdc_read(buf, sizeof(buf));
+        // read and echo back
+        uint32_t count = tud_cdc_read(buf, sizeof(buf));
+
+        tud_cdc_write(buf, count);
+      }
 
-      tud_cdc_write(buf, count);
       tud_cdc_write_flush();
     }
+  }
+}
 
-    taskYIELD();
+void tud_cdc_line_state_cb(uint8_t itf, bool dtr, bool rts)
+{
+  (void) itf;
+
+  // connected
+  if ( dtr && rts )
+  {
+    // print greeting
+    tud_cdc_write_str("tinyusb usb cdc\n");
   }
 }
 #endif
diff --git a/examples/device/nrf52840_freertos/segger/SEGGER_RTT.c b/examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT.c
similarity index 100%
rename from examples/device/nrf52840_freertos/segger/SEGGER_RTT.c
rename to examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT.c
diff --git a/examples/device/nrf52840_freertos/segger/SEGGER_RTT.h b/examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT.h
similarity index 100%
rename from examples/device/nrf52840_freertos/segger/SEGGER_RTT.h
rename to examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT.h
diff --git a/examples/device/nrf52840_freertos/segger/SEGGER_RTT_Conf.h b/examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT_Conf.h
similarity index 100%
rename from examples/device/nrf52840_freertos/segger/SEGGER_RTT_Conf.h
rename to examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT_Conf.h
diff --git a/examples/device/nrf52840_freertos/segger/SEGGER_RTT_SES.c b/examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT_SES.c
similarity index 100%
rename from examples/device/nrf52840_freertos/segger/SEGGER_RTT_SES.c
rename to examples/device/nrf52840_freertos/src/segger_rtt/SEGGER_RTT_SES.c
diff --git a/examples/device/nrf52840_freertos/src/tusb_config.h b/examples/device/nrf52840_freertos/src/tusb_config.h
index 96d851f9..9641f7bd 100644
--- a/examples/device/nrf52840_freertos/src/tusb_config.h
+++ b/examples/device/nrf52840_freertos/src/tusb_config.h
@@ -55,7 +55,7 @@
 
 /*------------- RTOS -------------*/
 #define CFG_TUSB_OS                 OPT_OS_FREERTOS
-#define CFG_TUD_TASK_PRIO           (configMAX_PRIORITIES-3)
+#define CFG_TUD_TASK_PRIO           (configMAX_PRIORITIES-1)
 //#define CFG_TUD_TASK_QUEUE_SZ     16
 //#define CFG_TUD_TASK_STACK_SZ     150
 
diff --git a/hw/bsp/pca10056/board_pca10056.c b/hw/bsp/pca10056/board_pca10056.c
index 928c39ac..54b1488a 100644
--- a/hw/bsp/pca10056/board_pca10056.c
+++ b/hw/bsp/pca10056/board_pca10056.c
@@ -98,6 +98,11 @@ void board_init(void)
   nrf_gpio_cfg_output(BOARD_LED2);
   nrf_gpio_cfg_output(BOARD_LED3);
 
+  board_led_control(BOARD_LED0, false);
+  board_led_control(BOARD_LED1, false);
+  board_led_control(BOARD_LED2, false);
+  board_led_control(BOARD_LED3, false);
+
   // Button
   for(uint8_t i=0; i<BOARD_BUTTON_COUNT; i++) nrf_gpio_cfg_input(_button_pins[i], NRF_GPIO_PIN_PULLUP);
 
diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index a6f1f1fb..392ad349 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -71,8 +71,10 @@ typedef struct
   uint8_t rx_ff_buf[CFG_TUD_CDC_RX_BUFSIZE];
   uint8_t tx_ff_buf[CFG_TUD_CDC_TX_BUFSIZE];
 
+#if CFG_FIFO_MUTEX
   osal_mutex_def_t rx_ff_mutex;
   osal_mutex_def_t tx_ff_mutex;
+#endif
 
   // Endpoint Transfer buffer
   CFG_TUSB_MEM_ALIGN uint8_t epout_buf[CFG_TUD_CDC_EPSIZE];
@@ -151,6 +153,11 @@ uint32_t tud_cdc_n_write_char(uint8_t itf, char ch)
   return tud_cdc_n_write(itf, &ch, 1);
 }
 
+uint32_t tud_cdc_n_write_str (uint8_t itf, char const* str)
+{
+  return tud_cdc_n_write(itf, str, strlen(str));
+}
+
 uint32_t tud_cdc_n_write(uint8_t itf, void const* buffer, uint32_t bufsize)
 {
   uint16_t ret = tu_fifo_write_n(&_cdcd_itf[itf].tx_ff, buffer, bufsize);
@@ -203,10 +210,12 @@ void cdcd_init(void)
 
     // config fifo
     tu_fifo_config(&ser->rx_ff, ser->rx_ff_buf, CFG_TUD_CDC_RX_BUFSIZE, 1, true);
-    tu_fifo_config_mutex(&ser->rx_ff, osal_mutex_create(&ser->rx_ff_mutex));
-
     tu_fifo_config(&ser->tx_ff, ser->tx_ff_buf, CFG_TUD_CDC_TX_BUFSIZE, 1, false);
+
+#if CFG_FIFO_MUTEX
+    tu_fifo_config_mutex(&ser->rx_ff, osal_mutex_create(&ser->rx_ff_mutex));
     tu_fifo_config_mutex(&ser->tx_ff, osal_mutex_create(&ser->tx_ff_mutex));
+#endif
   }
 }
 
diff --git a/src/class/cdc/cdc_device.h b/src/class/cdc/cdc_device.h
index 2e03793a..f1bd3395 100644
--- a/src/class/cdc/cdc_device.h
+++ b/src/class/cdc/cdc_device.h
@@ -77,6 +77,7 @@ char     tud_cdc_n_peek            (uint8_t itf, int pos);
 
 uint32_t tud_cdc_n_write_char      (uint8_t itf, char ch);
 uint32_t tud_cdc_n_write           (uint8_t itf, void const* buffer, uint32_t bufsize);
+uint32_t tud_cdc_n_write_str       (uint8_t itf, char const* str);
 bool     tud_cdc_n_write_flush     (uint8_t itf);
 
 //--------------------------------------------------------------------+
@@ -95,6 +96,7 @@ static inline char     tud_cdc_peek            (int pos)
 
 static inline uint32_t tud_cdc_write_char      (char ch)                              { return tud_cdc_n_write_char(0, ch);         }
 static inline uint32_t tud_cdc_write           (void const* buffer, uint32_t bufsize) { return tud_cdc_n_write(0, buffer, bufsize); }
+static inline uint32_t tud_cdc_write_str       (char const* str)                      { return tud_cdc_n_write_str(0, str);         }
 static inline bool     tud_cdc_write_flush     (void)                                 { return tud_cdc_n_write_flush(0);            }
 
 //--------------------------------------------------------------------+
diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index e0b3d0aa..2acd4b69 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -42,25 +42,16 @@
 #include "tusb_fifo.h"
 
 // implement mutex lock and unlock
-// For OSAL_NONE: if mutex is locked by other, function return immediately (since there is no task context)
-// For Real RTOS: fifo lock is a blocking API
 #if CFG_FIFO_MUTEX
 
-static bool tu_fifo_lock(tu_fifo_t *f)
+static void tu_fifo_lock(tu_fifo_t *f)
 {
   if (f->mutex)
   {
-#if CFG_TUSB_OS == OPT_OS_NONE
-    // There is no subtask context for blocking mutex, we will check and return if cannot lock the mutex
-    if ( !osal_mutex_lock_notask(f->mutex) ) return false;
-#else
     uint32_t err;
     (void) err;
     osal_mutex_lock(f->mutex, OSAL_TIMEOUT_WAIT_FOREVER, &err);
-#endif
   }
-
-  return true;
 }
 
 static void tu_fifo_unlock(tu_fifo_t *f)
@@ -73,14 +64,14 @@ static void tu_fifo_unlock(tu_fifo_t *f)
 
 #else
 
-#define tu_fifo_lock(_ff)       true
+#define tu_fifo_lock(_ff)
 #define tu_fifo_unlock(_ff)
 
 #endif
 
 bool tu_fifo_config(tu_fifo_t *f, void* buffer, uint16_t depth, uint16_t item_size, bool overwritable)
 {
-  if ( !tu_fifo_lock(f) ) return false;
+  tu_fifo_lock(f);
 
   f->buffer = (uint8_t*) buffer;
   f->depth  = depth;
@@ -115,7 +106,7 @@ bool tu_fifo_read(tu_fifo_t* f, void * p_buffer)
 {
   if( tu_fifo_empty(f) ) return false;
 
-  if ( !tu_fifo_lock(f) ) return false;
+  tu_fifo_lock(f);
 
   memcpy(p_buffer,
          f->buffer + (f->rd_idx * f->item_size),
@@ -216,7 +207,7 @@ bool tu_fifo_write (tu_fifo_t* f, const void * p_data)
 {
   if ( tu_fifo_full(f) && !f->overwritable ) return false;
 
-  if ( !tu_fifo_lock(f) ) return false;
+  tu_fifo_lock(f);
 
   memcpy( f->buffer + (f->wr_idx * f->item_size),
           p_data,
@@ -279,7 +270,7 @@ uint16_t tu_fifo_write_n (tu_fifo_t* f, const void * p_data, uint16_t count)
 /******************************************************************************/
 bool tu_fifo_clear(tu_fifo_t *f)
 {
-  if ( !tu_fifo_lock(f) ) return false;
+  tu_fifo_lock(f);
 
   f->rd_idx = f->wr_idx = f->count = 0;
 
diff --git a/src/common/tusb_fifo.h b/src/common/tusb_fifo.h
index 70dc087c..61d92b60 100644
--- a/src/common/tusb_fifo.h
+++ b/src/common/tusb_fifo.h
@@ -43,7 +43,9 @@
 #ifndef _TUSB_FIFO_H_
 #define _TUSB_FIFO_H_
 
-#define CFG_FIFO_MUTEX      1
+// mutex is only needed for RTOS
+// for OS None, we don't get preempted
+#define CFG_FIFO_MUTEX      (CFG_TUSB_OS != OPT_OS_NONE)
 
 #include <stdint.h>
 #include <stdbool.h>
diff --git a/src/osal/osal_none.h b/src/osal/osal_none.h
index 796ddc15..f70c99c7 100644
--- a/src/osal/osal_none.h
+++ b/src/osal/osal_none.h
@@ -178,19 +178,6 @@ static inline osal_mutex_t osal_mutex_create(osal_mutex_def_t* mdef)
 #define osal_mutex_unlock(_mutex_hdl)   osal_semaphore_post(_mutex_hdl, false)
 #define osal_mutex_lock                 osal_semaphore_wait
 
-// check if mutex is available for non-thread/substask usage in some cases
-static inline bool osal_mutex_lock_notask(osal_mutex_t mutex_hdl)
-{
-  if (mutex_hdl->count)
-  {
-    mutex_hdl->count--;
-    return true;
-  }else
-  {
-    return false;
-  }
-}
-
 //--------------------------------------------------------------------+
 // QUEUE API
 //--------------------------------------------------------------------+