1 files changed, 19 insertions, 1 deletions

diff --git a/firmware/usbstack/usb_storage.c b/firmware/usbstack/usb_storage.c
index 3ee7acfab5..f233549a2b 100644
--- a/firmware/usbstack/usb_storage.c
+++ b/firmware/usbstack/usb_storage.c
@@ -34,6 +34,14 @@
 
 #ifdef USB_STORAGE
 
+/* The SD card driver on Sansa c200 and e200 can cause write corruption,
+ * often triggered by simultaneous USB activity. This can be largely avoided
+ * by not overlapping ata_write_sector() with USB transfers. This does reduce
+ * write performance, so we only do it for the affected DAPs
+ */
+#if defined(SANSA_C200) || defined(SANSA_E200)
+#define SERIALIZE_WRITES
+#endif
 /* Enable the following define to export only the SD card slot. This
  * is useful for USBCV MSC tests, as those are destructive.
  * This won't work right if the device doesn't have a card slot.
@@ -408,12 +416,15 @@ void usb_storage_transfer_complete(int ep,bool in,int status,int length)
                              (BUFFER_SIZE/SECTOR_SIZE);
                 unsigned int next_count = cur_cmd.count -
                              MIN(cur_cmd.count,BUFFER_SIZE/SECTOR_SIZE);
+                int next_select = !cur_cmd.data_select;
 
+#ifndef SERIALIZE_WRITES
                 if(next_count!=0) {
                     /* Ask the host to send more, to the other buffer */
-                    receive_block_data(cur_cmd.data[!cur_cmd.data_select],
+                    receive_block_data(cur_cmd.data[next_select],
                                        MIN(BUFFER_SIZE,next_count*SECTOR_SIZE));
                 }
+#endif
 
                 /* Now write the data that just came in, while the host is
                    sending the next bit */
@@ -429,6 +440,13 @@ void usb_storage_transfer_complete(int ep,bool in,int status,int length)
                     cur_sense_data.ascq=0;
                     break;
                 }
+#ifdef SERIALIZE_WRITES
+                if(next_count!=0) {
+                    /* Ask the host to send more, to the other buffer */
+                    receive_block_data(cur_cmd.data[next_select],
+                                       MIN(BUFFER_SIZE,next_count*SECTOR_SIZE));
+                }
+#endif
 
                 if(next_count==0) {
                     send_csw(UMS_STATUS_GOOD);