diff --git a/firmware/common/file.c b/firmware/common/file.c
index 3477c10..89fbe4c 100644
--- a/firmware/common/file.c
+++ b/firmware/common/file.c
@@ -28,6 +28,8 @@
 #include "dircache.h"
 #include "filefuncs.h"
 #include "system.h"
+#define LOGF_ENABLE
+#include "logf.h"
 
 /*
   These functions provide a roughly POSIX-compatible file IO API.
@@ -60,6 +62,20 @@ int file_creat(const char *pathname)
     return open(pathname, O_WRONLY|O_CREAT|O_TRUNC, 0666);
 }
 
+void dbg_print_open_files(void)
+{
+    char path[MAX_PATH];
+    logf("open files: (*dirty)");
+    for(int  i = 0; i < MAX_OPEN_FILES; i++)
+    {
+        if(!openfiles[i].busy)
+            continue;
+        if(!fat_get_file_name(&openfiles[i].fatfile, path, MAX_PATH))
+            strcpy(path, "<error>");
+        logf("  %s%s", openfiles[i].dirty ? "*" : "", path);
+    }
+}
+
 static int open_internal(const char* pathname, int flags, bool use_cache)
 {
     DIR_UNCACHED* dir;
diff --git a/firmware/drivers/fat.c b/firmware/drivers/fat.c
index f055f4b..568692d 100644
--- a/firmware/drivers/fat.c
+++ b/firmware/drivers/fat.c
@@ -2556,3 +2556,25 @@ bool fat_ismounted(int volume)
     return (volume<NUM_VOLUMES && fat_bpbs[volume].mounted);
 }
 #endif
+
+bool fat_get_file_name(struct fat_file *file, char *path, long len)
+{
+    static struct fat_dir dir;
+    struct fat_direntry direntry;
+
+    memset(&dir, 0, sizeof(dir));
+    memset(&direntry, 0, sizeof(direntry));
+
+    int rc = fat_opendir(IF_MV2(file->volume,) &dir, file->dircluster, NULL);
+    if(rc < 0)
+        return false;
+    while(fat_getnext(&dir, &direntry) >= 0)
+    {
+        if(direntry.firstcluster == file->firstcluster || direntry.name[0] == 0)
+            break;
+    }
+    if(direntry.name[0] == 0)
+        return false;
+    strlcpy(path, direntry.name, len);
+    return true;
+}
diff --git a/firmware/export/fat.h b/firmware/export/fat.h
index 36beda7..9550045 100644
--- a/firmware/export/fat.h
+++ b/firmware/export/fat.h
@@ -134,4 +134,6 @@ extern int fat_getnext(struct fat_dir *ent, struct fat_direntry *entry);
 extern unsigned int fat_get_cluster_size(IF_MV_NONVOID(int volume)); /* public for debug info screen */
 extern bool fat_ismounted(int volume);
 
+extern bool fat_get_file_name(struct fat_file *file, char *path, long len);
+
 #endif
diff --git a/firmware/usb.c b/firmware/usb.c
index ebbf080..25cbe24 100644
--- a/firmware/usb.c
+++ b/firmware/usb.c
@@ -217,6 +217,9 @@ static inline void usb_slave_mode(bool on)
     int rc;
 
     if(on)
+        dbg_print_open_files();
+
+    if(on)
     {
         trigger_cpu_boost();
 #ifdef HAVE_PRIORITY_SCHEDULING