diff --git a/.gdbinit b/.gdbinit
new file mode 100644
index 00000000..782c767c
--- /dev/null
+++ b/.gdbinit
@@ -0,0 +1 @@
+target extended-remote localhost:3333
diff --git a/inc/cdc_enumerate.h b/inc/cdc_enumerate.h
index f609cc2c..16f15641 100644
--- a/inc/cdc_enumerate.h
+++ b/inc/cdc_enumerate.h
@@ -130,6 +130,7 @@ typedef struct {
 
 uint32_t USB_Read(void *pData, uint32_t length, uint32_t ep);
 uint32_t USB_Write(const void *pData, uint32_t length, uint8_t ep_num);
+uint32_t USB_WriteCore(const void *pData, uint32_t length, uint8_t ep_num, bool handoverMode);
 void USB_ReadBlocking(void *dst, uint32_t length, uint32_t ep, PacketBuffer *cache);
 uint32_t USB_ReadCore(void *pData, uint32_t length, uint32_t ep, PacketBuffer *cache);
 bool USB_Ok(void);
diff --git a/src/cdc_enumerate.c b/src/cdc_enumerate.c
index 788f0de7..c9406972 100644
--- a/src/cdc_enumerate.c
+++ b/src/cdc_enumerate.c
@@ -443,6 +443,10 @@ void USB_ReadBlocking(void *dst, uint32_t length, uint32_t ep, PacketBuffer *cac
 }
 
 uint32_t USB_Write(const void *pData, uint32_t length, uint8_t ep_num) {
+    return USB_WriteCore(pData, length, ep_num, false);
+}
+
+uint32_t USB_WriteCore(const void *pData, uint32_t length, uint8_t ep_num, bool handoverMode) {
     Usb *pUsb = pCdc.pUsb;
     uint32_t data_address;
 
@@ -450,6 +454,7 @@ uint32_t USB_Write(const void *pData, uint32_t length, uint8_t ep_num) {
 
     /* Check for requirement for multi-packet or auto zlp */
     if (length >= (1 << (epdesc->DeviceDescBank[1].PCKSIZE.bit.SIZE + 3))) {
+        assert(!handoverMode);
         /* Update the EP data address */
         data_address = (uint32_t)pData;
         // data must be in RAM!
@@ -457,6 +462,8 @@ uint32_t USB_Write(const void *pData, uint32_t length, uint8_t ep_num) {
 
         // always disable AUTO_ZLP on MSC channel, otherwise enable
         epdesc->DeviceDescBank[1].PCKSIZE.bit.AUTO_ZLP = ep_num == USB_EP_MSC_IN ? false : true;
+    } else if (handoverMode) {
+        data_address = (uint32_t)pData;
     } else {
         /* Copy to local buffer */
         memcpy(endpointCache[ep_num].buf, pData, length);
@@ -478,8 +485,8 @@ uint32_t USB_Write(const void *pData, uint32_t length, uint8_t ep_num) {
 
     /* Wait for transfer to complete */
     while (!(pUsb->DEVICE.DeviceEndpoint[ep_num].EPINTFLAG.reg & USB_DEVICE_EPINTFLAG_TRCPT1)) {
-        if (ep_num && !USB_Ok())
-            return -1;
+        // if (ep_num && !USB_Ok())
+        //    return -1;
     }
 
     return length;
diff --git a/src/msc.c b/src/msc.c
index 0d91626d..1fa0eaa1 100644
--- a/src/msc.c
+++ b/src/msc.c
@@ -695,6 +695,12 @@ static void udi_msc_sbc_trans(bool b_read) {
             USB_Write(block_buffer, UDI_MSC_BLOCK_SIZE, USB_EP_MSC_IN);
         } else {
             USB_ReadBlocking(block_buffer, UDI_MSC_BLOCK_SIZE, USB_EP_MSC_OUT, 0);
+
+#if 0
+            check_uf2_handover(block_buffer, udi_msc_nb_block - i - 1, USB_EP_MSC_IN,
+                               USB_EP_MSC_OUT, udi_msc_cbw.dCBWTag);
+#endif
+
             write_block(udi_msc_addr + i, block_buffer, false);
         }
         udi_msc_csw.dCSWDataResidue -= UDI_MSC_BLOCK_SIZE;
@@ -724,7 +730,7 @@ static void process_handover_initial(UF2_HandoverArgs *handover, PacketBuffer *h
     // read-write remaining blocks
     handover_flash(handover, handoverCache);
     // send USB response, as the user space isn't gonna do it
-    USB_Write((void *)&csw, sizeof(csw), handover->ep_in);
+    USB_WriteCore((void *)&csw, sizeof(csw), handover->ep_in, true);
 }
 
 static void process_handover(UF2_HandoverArgs *handover, PacketBuffer *handoverCache) {
@@ -761,7 +767,7 @@ static void process_handover(UF2_HandoverArgs *handover, PacketBuffer *handoverC
         break;
     }
 
-    USB_Write((void *)&csw, sizeof(csw), handover->ep_in);
+    USB_WriteCore((void *)&csw, sizeof(csw), handover->ep_in, true);
 }
 
 static void handover(UF2_HandoverArgs *args) {
@@ -769,7 +775,10 @@ static void handover(UF2_HandoverArgs *args) {
     // interrupt handlers from user space
     SCB->VTOR = 0;
 
-    PacketBuffer cache;
+	USB->DEVICE.INTENCLR.reg = USB_DEVICE_INTENCLR_MASK;
+	USB->DEVICE.INTFLAG.reg = USB_DEVICE_INTFLAG_MASK;
+
+    PacketBuffer cache = {0};
 
     // They may have 0x80 bit set
     args->ep_in &= 0xf;