diff --git a/test/security_manager_sc/Makefile b/test/security_manager_sc/Makefile
index a03a748c6..ac264d3c9 100644
--- a/test/security_manager_sc/Makefile
+++ b/test/security_manager_sc/Makefile
@@ -79,7 +79,7 @@ VPATH += ${BTSTACK_ROOT}/chipset/zephyr
 CFLAGS  += $(shell pkg-config libusb-1.0 --cflags)
 LDFLAGS += $(shell pkg-config libusb-1.0 --libs)
 
-CFLAGS += -fprofile-arcs -ftest-coverage -fsanitize=address,undefined
+CFLAGS += -fprofile-arcs -ftest-coverage -fsanitize=address,undefined -DCOVERAGE
 
 CORE_OBJ    = $(CORE:.c=.o)
 COMMON_OBJ  = $(COMMON:.c=.o) 
diff --git a/test/security_manager_sc/sm_test.c b/test/security_manager_sc/sm_test.c
index f451c9484..f2d0e5388 100644
--- a/test/security_manager_sc/sm_test.c
+++ b/test/security_manager_sc/sm_test.c
@@ -62,7 +62,12 @@
 #include "hci_dump.h"
 #include "l2cap.h"
 #include "btstack_stdin.h"
- 
+
+#ifdef COVERAGE
+// guesswork:
+void __gcov_flush(void);
+#endif
+
 #define HEARTBEAT_PERIOD_MS 1000
 
 const uint8_t adv_data[] = {
@@ -343,6 +348,7 @@ static void app_packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *
 }
 
 static void stdin_process(char c){
+	log_info("stdin: %c (%02x)", c, c);
     // passkey input
     if (ui_digits_for_passkey && c >= '0' && c <= '9'){
         printf("%c", c);
@@ -422,7 +428,11 @@ static void stdin_process(char c){
             sm_request_pairing(connection_handle);
             break;
         case 'x':
-            printf("Exit\n");
+#ifdef COVERAGE
+			log_info("Flush gcov");
+			__gcov_flush();
+#endif
+			printf("EXIT\n");
             exit(0);
             break;
         default:
diff --git a/test/security_manager_sc/sm_test.py b/test/security_manager_sc/sm_test.py
index 285099b3e..fadb6ea42 100755
--- a/test/security_manager_sc/sm_test.py
+++ b/test/security_manager_sc/sm_test.py
@@ -49,7 +49,7 @@ failures = [
 debug      = False
 regenerate = False
 # usb_paths = ['4', '6']
-usb_paths = ['3', '5']
+usb_paths = ['1', '2']
 
 class Node:
 
@@ -117,7 +117,7 @@ class Node:
         args.append('-o')
         args.append(self.oob_data)
         print('%s - "%s"' % (self.name, ' '.join(args)))
-        self.p = subprocess.Popen(args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+        self.p = subprocess.Popen(args, bufsize=0, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
         (self.stdin, self.stdout) = (self.p.stdin, self.p.stdout)
         self.linebuffer = ''
 
@@ -137,10 +137,13 @@ class Node:
         self.peer_addr = addr
 
     def write(self, string):
-        self.stdin.write(string)
+        self.stdin.write(string.encode('utf-8'))
 
     def terminate(self):
         self.write('x')
+        # wait for 'EXIT' message indicating coverage data was written
+        while not self.got_line():
+            self.read_stdout()
         self.p.terminate()
 
 def run(test_descriptor, nodes):