diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index fc124627..7d9e196a 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -357,7 +357,7 @@ bool cdcd_control_request(uint8_t rhport, tusb_control_request_t const * request
   return true;
 }
 
-tusb_error_t cdcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes)
+bool cdcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes)
 {
   (void) result;
 
@@ -382,13 +382,13 @@ tusb_error_t cdcd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result,
     // invoke receive callback (if there is still data)
     if (tud_cdc_rx_cb && tu_fifo_count(&p_cdc->rx_ff) ) tud_cdc_rx_cb(itf);
 
-    // prepare for next
-    TU_ASSERT( dcd_edpt_xfer(rhport, p_cdc->ep_out, p_cdc->epout_buf, CFG_TUD_CDC_EPSIZE), TUSB_ERROR_DCD_EDPT_XFER );
+    // prepare for incoming data
+    TU_ASSERT( dcd_edpt_xfer(rhport, p_cdc->ep_out, p_cdc->epout_buf, CFG_TUD_CDC_EPSIZE) );
   }
 
   // nothing to do with in and notif endpoint
 
-  return TUSB_ERROR_NONE;
+  return true;
 }
 
 #endif
diff --git a/src/class/cdc/cdc_device.h b/src/class/cdc/cdc_device.h
index 03aa2485..5ee649c4 100644
--- a/src/class/cdc/cdc_device.h
+++ b/src/class/cdc/cdc_device.h
@@ -116,7 +116,7 @@ void cdcd_init               (void);
 bool cdcd_open               (uint8_t rhport, tusb_desc_interface_t const * p_interface_desc, uint16_t *p_length);
 bool cdcd_control_request (uint8_t rhport, tusb_control_request_t const * p_request);
 bool cdcd_control_request_complete (uint8_t rhport, tusb_control_request_t const * p_request);
-tusb_error_t cdcd_xfer_cb            (uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes);
+bool cdcd_xfer_cb            (uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint32_t xferred_bytes);
 void cdcd_reset              (uint8_t rhport);
 
 #endif
diff --git a/src/class/custom/custom_device.c b/src/class/custom/custom_device.c
index bec6f42d..129d405a 100644
--- a/src/class/custom/custom_device.c
+++ b/src/class/custom/custom_device.c
@@ -71,22 +71,22 @@ void cusd_init(void)
   tu_varclr(&_cusd_itf);
 }
 
-tusb_error_t cusd_open(uint8_t rhport, tusb_desc_interface_t const * p_desc_itf, uint16_t *p_len)
+bool cusd_open(uint8_t rhport, tusb_desc_interface_t const * p_desc_itf, uint16_t *p_len)
 {
   cusd_interface_t* p_itf = &_cusd_itf;
 
   // Open endpoint pair with usbd helper
-  tusb_desc_endpoint_t const *p_desc_ep = (tusb_desc_endpoint_t const *) tu_desc_next( (uint8_t const*) p_desc_itf );
-  TU_ASSERT_ERR( usbd_open_edpt_pair(rhport, p_desc_ep, TUSB_XFER_BULK, &p_itf->ep_out, &p_itf->ep_in) );
+  tusb_desc_endpoint_t const *p_desc_ep = (tusb_desc_endpoint_t const *) tu_desc_next(p_desc_itf);
+  TU_ASSERT( usbd_open_edpt_pair(rhport, p_desc_ep, TUSB_XFER_BULK, &p_itf->ep_out, &p_itf->ep_in) );
 
   p_itf->itf_num = p_desc_itf->bInterfaceNumber;
 
   (*p_len) = sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t);
 
   // TODO Prepare for incoming data
-//  TU_ASSERT( dcd_edpt_xfer(rhport, p_itf->ep_out, (uint8_t*) &p_msc->cbw, sizeof(msc_cbw_t)), TUSB_ERROR_DCD_EDPT_XFER );
+//  TU_ASSERT( dcd_edpt_xfer(rhport, p_itf->ep_out, (uint8_t*) &p_msc->cbw, sizeof(msc_cbw_t)) );
 
-  return TUSB_ERROR_NONE;
+  return true;
 }
 
 bool cusd_control_request(uint8_t rhport, tusb_control_request_t const * p_request)
@@ -94,9 +94,9 @@ bool cusd_control_request(uint8_t rhport, tusb_control_request_t const * p_reque
   return false;
 }
 
-tusb_error_t cusd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
+bool cusd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
 {
-  return TUSB_ERROR_NONE;
+  return true;
 }
 
 void cusd_reset(uint8_t rhport)
diff --git a/src/class/custom/custom_device.h b/src/class/custom/custom_device.h
index f223a4d3..aae06d50 100644
--- a/src/class/custom/custom_device.h
+++ b/src/class/custom/custom_device.h
@@ -63,10 +63,10 @@
 #ifdef _TINY_USB_SOURCE_FILE_
 
 void cusd_init(void);
-tusb_error_t cusd_open(uint8_t rhport, tusb_desc_interface_t const * p_interface_desc, uint16_t *p_length);
+bool cusd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length);
 bool cusd_control_request_st(uint8_t rhport, tusb_control_request_t const * p_request);
 bool cusd_control_request_complete (uint8_t rhport, tusb_control_request_t const * p_request);
-tusb_error_t cusd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
+bool cusd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
 void cusd_reset(uint8_t rhport);
 #endif
 
diff --git a/src/class/hid/hid_device.c b/src/class/hid/hid_device.c
index cfb1a698..bd49c157 100644
--- a/src/class/hid/hid_device.c
+++ b/src/class/hid/hid_device.c
@@ -508,10 +508,10 @@ bool hidd_control_request_complete(uint8_t rhport, tusb_control_request_t const
   return true;
 }
 
-tusb_error_t hidd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
+bool hidd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
 {
   // nothing to do
-  return TUSB_ERROR_NONE;
+  return true;
 }
 
 
diff --git a/src/class/hid/hid_device.h b/src/class/hid/hid_device.h
index 2f0047d8..885f3344 100644
--- a/src/class/hid/hid_device.h
+++ b/src/class/hid/hid_device.h
@@ -380,7 +380,7 @@ void hidd_init(void);
 bool hidd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length);
 bool hidd_control_request(uint8_t rhport, tusb_control_request_t const * p_request);
 bool hidd_control_request_complete (uint8_t rhport, tusb_control_request_t const * p_request);
-tusb_error_t hidd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
+bool hidd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
 void hidd_reset(uint8_t rhport);
 
 #endif
diff --git a/src/class/msc/msc_device.c b/src/class/msc/msc_device.c
index 14a7e593..d4d115bc 100644
--- a/src/class/msc/msc_device.c
+++ b/src/class/msc/msc_device.c
@@ -329,7 +329,7 @@ int32_t proc_builtin_scsi(msc_cbw_t const * p_cbw, uint8_t* buffer, uint32_t buf
   return ret;
 }
 
-tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
+bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes)
 {
   mscd_interface_t* p_msc = &_mscd_itf;
   msc_cbw_t const * p_cbw = &p_msc->cbw;
@@ -340,10 +340,10 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event,
     case MSC_STAGE_CMD:
       //------------- new CBW received -------------//
       // Complete IN while waiting for CMD is usually Status of previous SCSI op, ignore it
-      if(ep_addr != p_msc->ep_out) return TUSB_ERROR_NONE;
+      if(ep_addr != p_msc->ep_out) return true;
 
       TU_ASSERT( event == XFER_RESULT_SUCCESS &&
-                 xferred_bytes == sizeof(msc_cbw_t) && p_cbw->signature == MSC_CBW_SIGNATURE, TUSB_ERROR_INVALID_PARA );
+                 xferred_bytes == sizeof(msc_cbw_t) && p_cbw->signature == MSC_CBW_SIGNATURE );
 
       p_csw->signature    = MSC_CSW_SIGNATURE;
       p_csw->tag          = p_cbw->tag;
@@ -388,7 +388,7 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event,
         else if ( !BIT_TEST_(p_cbw->dir, 7) )
         {
           // OUT transfer
-          TU_ASSERT( dcd_edpt_xfer(rhport, p_msc->ep_out, _mscd_buf, p_msc->total_len), TUSB_ERROR_DCD_EDPT_XFER );
+          TU_ASSERT( dcd_edpt_xfer(rhport, p_msc->ep_out, _mscd_buf, p_msc->total_len) );
         }
         else
         {
@@ -409,8 +409,8 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event,
             p_msc->total_len = (uint32_t) cb_result;
             p_csw->status = MSC_CSW_STATUS_PASSED;
 
-            TU_ASSERT( p_cbw->total_bytes >= p_msc->total_len, TUSB_ERROR_INVALID_PARA ); // cannot return more than host expect
-            TU_ASSERT( dcd_edpt_xfer(rhport, p_msc->ep_in, _mscd_buf, p_msc->total_len), TUSB_ERROR_DCD_EDPT_XFER );
+            TU_ASSERT( p_cbw->total_bytes >= p_msc->total_len ); // cannot return more than host expect
+            TU_ASSERT( dcd_edpt_xfer(rhport, p_msc->ep_in, _mscd_buf, p_msc->total_len) );
           }else
           {
             p_msc->total_len = 0;
@@ -474,7 +474,7 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event,
               // simulate an transfer complete with adjusted parameters --> this driver callback will fired again
               dcd_event_xfer_complete(rhport, p_msc->ep_out, xferred_bytes-nbytes, XFER_RESULT_SUCCESS, false);
 
-              return TUSB_ERROR_NONE; // skip the rest
+              return true; // skip the rest
             }
             else
             {
@@ -549,7 +549,7 @@ tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event,
     }
   }
 
-  return TUSB_ERROR_NONE;
+  return true;
 }
 
 /*------------------------------------------------------------------*/
diff --git a/src/class/msc/msc_device.h b/src/class/msc/msc_device.h
index 80e47d84..c9e4139e 100644
--- a/src/class/msc/msc_device.h
+++ b/src/class/msc/msc_device.h
@@ -174,7 +174,7 @@ void mscd_init(void);
 bool mscd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint16_t *p_length);
 bool mscd_control_request(uint8_t rhport, tusb_control_request_t const * p_request);
 bool mscd_control_request_complete (uint8_t rhport, tusb_control_request_t const * p_request);
-tusb_error_t mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
+bool mscd_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t event, uint32_t xferred_bytes);
 void mscd_reset(uint8_t rhport);
 
 #endif
diff --git a/src/device/usbd.c b/src/device/usbd.c
index bf7fd950..8c685d5b 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -92,7 +92,7 @@ typedef struct {
   bool (* open           ) (uint8_t rhport, tusb_desc_interface_t const * desc_intf, uint16_t* p_length);
   bool (* control_request ) (uint8_t rhport, tusb_control_request_t const * request);
   bool (* control_request_complete ) (uint8_t rhport, tusb_control_request_t const * request);
-  tusb_error_t (* xfer_cb        ) (uint8_t rhport, uint8_t ep_addr, xfer_result_t, uint32_t);
+  bool (* xfer_cb        ) (uint8_t rhport, uint8_t ep_addr, xfer_result_t, uint32_t);
   void (* sof            ) (uint8_t rhport);
   void (* reset          ) (uint8_t);
 } usbd_class_driver_t;