diff --git a/examples/device/nrf52840/src/tusb_config.h b/examples/device/nrf52840/src/tusb_config.h
index 476ff4be..aee6099b 100644
--- a/examples/device/nrf52840/src/tusb_config.h
+++ b/examples/device/nrf52840/src/tusb_config.h
@@ -72,7 +72,9 @@
  *------------------------------------------------------------------*/
 
 // FIFO size of CDC TX and RX
-#define CFG_TUD_CDC_BUFSIZE         64
+#define CFG_TUD_CDC_RX_BUFSIZE    64
+#define CFG_TUD_CDC_TX_BUFSIZE    64
+
 
 // TX is sent automatically every Start of Frame event.
 // If not enabled, application must call tud_cdc_flush() periodically
diff --git a/examples/obsolete/device/src/tusb_config.h b/examples/obsolete/device/src/tusb_config.h
index bdadb211..3904facb 100644
--- a/examples/obsolete/device/src/tusb_config.h
+++ b/examples/obsolete/device/src/tusb_config.h
@@ -77,7 +77,9 @@
  *------------------------------------------------------------------*/
 
 // FIFO size of CDC TX and RX
-#define CFG_TUD_CDC_BUFSIZE       128
+#define CFG_TUD_CDC_RX_BUFSIZE    128
+#define CFG_TUD_CDC_TX_BUFSIZE    128
+
 
 // TX is sent automatically in Start of Frame event.
 // If not enabled, application must call tud_cdc_flush() periodically
diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index ccb15205..583180fc 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -67,17 +67,12 @@ typedef struct {
 
 // TODO multiple rhport
 
-#if CFG_TUSB_MCU == OPT_MCU_NRF5X
-// FIXME nrf52 OUT: Controller ACK data even we didn't prepare transfer
-CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[600];
-#else
-CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[64];
-#endif
 
+CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[64];
 CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_tx_buf[64];
 
-FIFO_DEF(_rx_ff, CFG_TUD_CDC_BUFSIZE, uint8_t, true);
-FIFO_DEF(_tx_ff, CFG_TUD_CDC_BUFSIZE, uint8_t, false);
+FIFO_DEF(_rx_ff, CFG_TUD_CDC_RX_BUFSIZE, uint8_t, true);
+FIFO_DEF(_tx_ff, CFG_TUD_CDC_TX_BUFSIZE, uint8_t, false);
 
 //--------------------------------------------------------------------+
 // INTERNAL OBJECT & FUNCTION DECLARATION
diff --git a/src/common/tusb_fifo.c b/src/common/tusb_fifo.c
index b4bb70b8..d6f34f33 100644
--- a/src/common/tusb_fifo.c
+++ b/src/common/tusb_fifo.c
@@ -37,6 +37,7 @@
 /**************************************************************************/
 
 #include "tusb_fifo.h"
+#include "common/tusb_verify.h" // for ASSERT
 
 /*------------------------------------------------------------------*/
 /*
@@ -207,7 +208,9 @@ bool fifo_peek_at(fifo_t* f, uint16_t position, void * p_buffer)
 bool fifo_write(fifo_t* f, void const * p_data)
 {
   if ( !fifo_initalized(f) ) return false;
-  if ( fifo_full(f) && !f->overwritable ) return false;
+
+//  if ( fifo_full(f) && !f->overwritable ) return false;
+  TU_ASSERT( !(fifo_full(f) && !f->overwritable) );
 
   mutex_lock_if_needed(f);
 
diff --git a/src/device/usbd.c b/src/device/usbd.c
index 0f6cebc6..a5819658 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -46,10 +46,12 @@
 #include "usbd.h"
 #include "device/usbd_pvt.h"
 
-#define USBD_TASK_QUEUE_DEPTH   16
+#ifndef CFG_TUD_TASK_QUEUE_SZ
+#define CFG_TUD_TASK_QUEUE_SZ   16
+#endif
 
-#ifndef CFG_TUD_TASK_STACKSIZE
-#define CFG_TUD_TASK_STACKSIZE 150
+#ifndef CFG_TUD_TASK_STACK_SZ
+#define CFG_TUD_TASK_STACK_SZ 150
 #endif
 
 #ifndef CFG_TUD_TASK_PRIO
@@ -190,10 +192,10 @@ typedef struct ATTR_ALIGNED(4)
 
 VERIFY_STATIC(sizeof(usbd_task_event_t) <= 12, "size is not correct");
 
-OSAL_TASK_DEF(_usbd_task_def, "usbd", usbd_task, CFG_TUD_TASK_PRIO, CFG_TUD_TASK_STACKSIZE);
+OSAL_TASK_DEF(_usbd_task_def, "usbd", usbd_task, CFG_TUD_TASK_PRIO, CFG_TUD_TASK_STACK_SZ);
 
 /*------------- event queue -------------*/
-OSAL_QUEUE_DEF(_usbd_qdef, USBD_TASK_QUEUE_DEPTH, usbd_task_event_t);
+OSAL_QUEUE_DEF(_usbd_qdef, CFG_TUD_TASK_QUEUE_SZ, usbd_task_event_t);
 static osal_queue_t _usbd_q;
 
 /*------------- control transfer semaphore -------------*/
@@ -547,12 +549,14 @@ void dcd_bus_event(uint8_t rhport, usbd_bus_event_type_t bus_event)
 
     case USBD_BUS_EVENT_SOF:
     {
+      #if CFG_TUD_CDC_FLUSH_ON_SOF
       usbd_task_event_t task_event =
       {
           .rhport          = rhport,
           .event_id        = USBD_EVT_SOF,
       };
       osal_queue_send_isr(_usbd_q, &task_event);
+      #endif
     }
     break;