diff --git a/classes/zephyr-flash-dfu.bbclass b/classes/zephyr-flash-dfu.bbclass
index 2d82281..b072d3b 100644
--- a/classes/zephyr-flash-dfu.bbclass
+++ b/classes/zephyr-flash-dfu.bbclass
@@ -6,8 +6,7 @@ python do_flash_usb() {
         bb.error("ERROR: dfu_util binary not in PATH")
         sys.exit(1)
 
-    board = d.getVar('BOARD',True)
-    bb.warn("Attempting to flash board: %s" % board)
+    board = d.getVar('BOARD', True)
 
     if board == 'arduino_101_sss':
         iface = 'sensor_core'
@@ -19,14 +18,39 @@ python do_flash_usb() {
         bb.error(" Unsupported board %s" % board)
         sys.exit(2)
 
+    # We need to serialize flashing of separate images (when using multiconfig)
+    lock = bb.utils.lockfile(os.path.join(d.getVar('TOPDIR', True),"flash-dfu.lock"), False, True)
     image = "%s/%s.elf" % (d.getVar('DEPLOY_DIR_IMAGE', True), d.getVar('PN', True))
     statement = 'dfu-util -v -a ' + iface + ' -d 8087:0aba -D ' + image.replace('elf','bin')
+
     bb.note("command: %s" % statement)
-    return_code = subprocess.call(statement, shell=True)
+    bb.plain("Attempting to flash board: %s" % board)
+
+    # Arduino-101 needs to be reset in order to enter "flash mode".
+    # The flash window is about 5 seconds.
+    # However, if the device is flashed, it remains in the "flash mode"
+    # until it is reset again, so it needs to enter the flash mode via reset
+    # only once even if we flash images for multiple cores. So we only prompt
+    # for reset once.
+
+    timeout = 5
+    promptneeded = True
+    while (timeout > 0):
+        time.sleep(0.5)
+        timeout = timeout - 0.5
+        return_code = subprocess.call(statement, shell=True)
+        if return_code == 0:
+            break
+        if promptneeded:
+            bb.warn("\n\n   *** Failed to flash %s. *** \n   Press reset, will retry for five seconds...\n" % board)
+            promptneeded = False
+
     if return_code != 0:
-        bb.error("Error flashig the device [%d], reset needed?" % return_code)
+        bb.error("Error flashing %s [%d]" % (board,return_code))
     else:
-        bb.warn("Success (return code %d)" % return_code)
+        bb.plain("Success (return code %d)" % return_code)
+
+    bb.utils.unlockfile(lock)
 }
 
 addtask do_flash_usb