follow up to pr #301

rename OPT_MCU_NUC505_USB_DMA to simply USE_DMA

src/portable/nuvoton/nuc505/dcd_nuc505.c

@@ -33,12 +33,6 @@
   nomenclature of EPA through EPL.
 */
 
-/*
-  Note on OPT_MCU_NUC505_USB_DMA: the author suggests against using this option.
-  The DMA functionality of the USBD peripheral does not appear to succeed with
-  transfer lengths that are longer (> 64 bytes) and are not a multiple of 4.
-*/
-
 #include "tusb_option.h"
 
 #if TUSB_OPT_DEVICE_ENABLED && (CFG_TUSB_MCU == OPT_MCU_NUC505)
@@ -46,6 +40,14 @@
 #include "device/dcd.h"
 #include "NUC505Series.h"
 
+/*
+  The DMA functionality of the USBD peripheral does not appear to succeed with
+  transfer lengths that are longer (> 64 bytes) and are not a multiple of 4.
+  Disable for now, we could implement a walk-around if non-DMA slow the MCU down
+  too much.
+*/
+#define USE_DMA     0
+
 /* rather important info unfortunately not provided by device include files */
 #define USBD_BUF_SIZE          2048 /* how much USB buffer space there is */
 #define USBD_MAX_DMA_LEN     0x1000 /* max bytes that can be DMAed at one time */
@@ -217,7 +219,7 @@ static void bus_reset(void)
   current_dma_xfer = NULL;
 }
 
-#ifdef OPT_MCU_NUC505_USB_DMA
+#if USE_DMA
 /* this must only be called by the ISR; it does its best to share the single DMA engine across all user EPs (IN and OUT) */
 static void service_dma(void)
 {
@@ -473,7 +475,7 @@ void USBD_IRQHandler(void)
 
     if (bus_state & USBD_BUSINTSTS_DMADONEIF_Msk)
     {
-#ifdef OPT_MCU_NUC505_USB_DMA
+#if USE_DMA
       if (current_dma_xfer)
       {
         current_dma_xfer->dma_requested = false;
@@ -607,7 +609,7 @@ void USBD_IRQHandler(void)
 
         if (out_ep)
         {
-#ifdef OPT_MCU_NUC505_USB_DMA
+#if USE_DMA
           xfer->dma_requested = true;
           service_dma();
 #else