Fix some targets fail to pass ticker overflow test

In mbed-os-tests-mbed_hal-common_tickers/Microsecond ticker overflow test, some targets
would fail to catch specified ticker value near overflow in time and so fail. This commit
alleviates the issue by checking ticker value range rather than one exact ticker value near
overflow.

Author: ccli8

TESTS/mbed_hal/common_tickers/main.cpp

@@ -29,8 +29,10 @@
 #define TICKER_INT_VAL 500
 #define TICKER_DELTA 10
 
-#define LP_TICKER_OVERFLOW_DELTA 0 // this will allow to detect that ticker counter rollovers to 0
-#define US_TICKER_OVERFLOW_DELTA 50
+#define LP_TICKER_OVERFLOW_DELTA1   0   // this will allow to detect that ticker counter rollovers to 0
+#define LP_TICKER_OVERFLOW_DELTA2   0
+#define US_TICKER_OVERFLOW_DELTA1   50
+#define US_TICKER_OVERFLOW_DELTA2   60
 
 #define TICKER_100_TICKS 100
 
@@ -48,7 +50,18 @@ using namespace utest::v1;
 volatile int intFlag = 0;
 const ticker_interface_t* intf;
 ticker_irq_handler_type prev_irq_handler;
-unsigned int ticker_overflow_delta;
+/* Some targets might fail overflow test uncertainly due to getting trapped in busy
+ * intf->read() loop. In the loop, some ticker values wouldn't get caught in time
+ * because of:
+ * 1. Lower CPU clock
+ * 2. Compiled code with worse performance
+ * 3. Interrupt at that time
+ * 
+ * We fix it by checking small ticker value range rather than one exact ticker point
+ * in near overflow check.
+ */
+unsigned int ticker_overflow_delta1;
+unsigned int ticker_overflow_delta2;
 
 /* Auxiliary function to count ticker ticks elapsed during execution of N cycles of empty while loop.
  * Parameter <step> is used to disable compiler optimisation. */
@@ -293,12 +306,13 @@ void ticker_overflow_test(void)
     intFlag = 0;
 
     /* Wait for max count. */
-    while (intf->read() != (max_count - ticker_overflow_delta)) {
+    while (intf->read() >= (max_count - ticker_overflow_delta2) &&
+        intf->read() <= (max_count - ticker_overflow_delta1)) {
         /* Just wait. */
     }
 
     /* Now we are near/at the overflow point. Detect rollover. */
-    while (intf->read() > ticker_overflow_delta);
+    while (intf->read() > ticker_overflow_delta1);
 
     const uint32_t after_overflow = intf->read();
 
@@ -310,7 +324,7 @@ void ticker_overflow_test(void)
     const uint32_t next_after_overflow = intf->read();
 
     /* Check that after the overflow ticker continue count. */
-    TEST_ASSERT(after_overflow <= ticker_overflow_delta);
+    TEST_ASSERT(after_overflow <= ticker_overflow_delta1);
     TEST_ASSERT(next_after_overflow >= TICKER_100_TICKS);
     TEST_ASSERT_EQUAL(0, intFlag);
 
@@ -465,7 +479,8 @@ utest::v1::status_t us_ticker_setup(const Case *const source, const size_t index
 
     prev_irq_handler = set_us_ticker_irq_handler(ticker_event_handler_stub);
 
-    ticker_overflow_delta = US_TICKER_OVERFLOW_DELTA;
+    ticker_overflow_delta1 = US_TICKER_OVERFLOW_DELTA1;
+    ticker_overflow_delta2 = US_TICKER_OVERFLOW_DELTA2;
 
     return greentea_case_setup_handler(source, index_of_case);
 }
@@ -493,7 +508,8 @@ utest::v1::status_t lp_ticker_setup(const Case *const source, const size_t index
 
     prev_irq_handler = set_lp_ticker_irq_handler(ticker_event_handler_stub);
 
-    ticker_overflow_delta = LP_TICKER_OVERFLOW_DELTA;
+    ticker_overflow_delta1 = LP_TICKER_OVERFLOW_DELTA1;
+    ticker_overflow_delta2 = LP_TICKER_OVERFLOW_DELTA2;
 
     return greentea_case_setup_handler(source, index_of_case);
 }