improve msc

src/class/msc/msc_device.c

@@ -161,22 +161,22 @@ uint16_t mscd_open(uint8_t rhport, tusb_desc_interface_t const * itf_desc, uint1
             MSC_SUBCLASS_SCSI == itf_desc->bInterfaceSubClass &&
             MSC_PROTOCOL_BOT  == itf_desc->bInterfaceProtocol, 0);
 
+  // msc driver length is fixed
+  enum { _MSC_DRIVER_LEN = sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t) };
+
   // Max length mus be at least 1 interface + 2 endpoints
-  TU_VERIFY(max_len >= sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t), 0);
+  TU_VERIFY(max_len >= _MSC_DRIVER_LEN, 0);
 
-  uint16_t len = 0;
   mscd_interface_t * p_msc = &_mscd_itf;
+  p_msc->itf_num = itf_desc->bInterfaceNumber;
 
   // Open endpoint pair
   TU_ASSERT( usbd_open_edpt_pair(rhport, tu_desc_next(itf_desc), 2, TUSB_XFER_BULK, &p_msc->ep_out, &p_msc->ep_in), 0 );
 
-  p_msc->itf_num = itf_desc->bInterfaceNumber;
-  len = sizeof(tusb_desc_interface_t) + 2*sizeof(tusb_desc_endpoint_t);
-
   // Prepare for Command Block Wrapper
   TU_ASSERT( usbd_edpt_xfer(rhport, p_msc->ep_out, (uint8_t*) &p_msc->cbw, sizeof(msc_cbw_t)), 0 );
 
-  return len;
+  return _MSC_DRIVER_LEN;
 }
 
 // Handle class control request