Add Timeout rescheduling test

The `Timeout` drift test uses rescheduling inside a callback, but it is
currently disabled due to lack of stability. Rescheduling using relative
timeouts inside the callback is a bad technique as it leads to drift, so
I understand the test being disabled. It is better to use `Ticker` for a
periodic callback or to use `Timeout::attach_absolute`.

Add a simpler test that just ensures the callback is called repeatedly -
this test would detect issue #12940, and should not have stability
problems.

TESTS/mbed_drivers/lp_timeout/main.cpp

@@ -52,6 +52,9 @@ Case cases[] = {
     Case("Zero delay (attach)", test_no_wait<AttachTester<LowPowerTimeout> >),
     Case("Zero delay (attach_us)", test_no_wait<AttachUSTester<LowPowerTimeout> >),
 
+    Case("Reschedule in callback (attach)",  test_reschedule<AttachTester<LowPowerTimeout> >),
+    Case("Reschedule in callback (attach_us)", test_reschedule<AttachUSTester<LowPowerTimeout> >),
+
     Case("10 ms delay accuracy (attach)", test_delay_accuracy<AttachTester<LowPowerTimeout>, 10000, SHORT_DELTA_US>,
          greentea_failure_handler),
     Case("10 ms delay accuracy (attach_us)", test_delay_accuracy<AttachUSTester<LowPowerTimeout>, 10000, SHORT_DELTA_US>,

TESTS/mbed_drivers/timeout/main.cpp

@@ -48,6 +48,9 @@ Case cases[] = {
     Case("Zero delay (attach)", test_no_wait<AttachTester<Timeout> >),
     Case("Zero delay (attach_us)", test_no_wait<AttachUSTester<Timeout> >),
 
+    Case("Reschedule in callback (attach)",  test_reschedule<AttachTester<Timeout> >),
+    Case("Reschedule in callback (attach_us)", test_reschedule<AttachUSTester<Timeout> >),
+
     Case("10 ms delay accuracy (attach)", test_delay_accuracy<AttachTester<Timeout>, 10000, SHORT_DELTA_US>,
          greentea_failure_handler),
     Case("10 ms delay accuracy (attach_us)", test_delay_accuracy<AttachUSTester<Timeout>, 10000, SHORT_DELTA_US>,

TESTS/mbed_drivers/timeout/timeout_tests.h

@@ -363,6 +363,27 @@ private:
     TimeoutTesterType _timeout;
 };
 
+/** Template for tests: rescheduling
+ *
+ * Given a Timeout object
+ * When a callback is attached with that reattaches itself, with @a attach()
+ * Then the callback is called repeatedly
+ *
+ * Given a Timeout object
+ * When a callback is attached with that reattaches itself, with @a attach_us()
+ * Then the callback is called repeatedly
+ */
+template<typename T>
+void test_reschedule(void)
+{
+    volatile uint32_t callback_count = 0;
+    TimeoutDriftTester<T> timeout;
+
+    timeout.reschedule_callback();
+    ThisThread::sleep_for(TEST_DELAY_MS * 5);
+    TEST_ASSERT(timeout.get_callback_count() >= 3);
+}
+
 /** Template for tests: accuracy of timeout delay scheduled repeatedly
  *
  * Test time drift -- device part