Enlarge wait time for flushing serial buffer in Greentea test code

Original wait time is not enough for UART to flush out before deepsleep/reset on some targets.

TESTS/mbed_hal/reset_reason/main.cpp

@@ -49,6 +49,22 @@
 #define MSG_KEY_RESET_REASON "reason"
 #define MSG_KEY_DEVICE_RESET "reset"
 
+/* Flush serial buffer before deep sleep/reset
+ *
+ * Since deepsleep()/reset would shut down the UART peripheral, we wait for some time
+ * to allow for hardware serial buffers to completely flush.
+ *
+ * Take NUMAKER_PFM_NUC472 as an example:
+ * Its UART peripheral has 16-byte Tx FIFO. With baud rate set to 9600, flush
+ * Tx FIFO would take: 16 * 8 * 1000 / 9600 = 13.3 (ms). So set wait time to
+ * 20ms here for safe.
+ *
+ * This should be replaced with a better function that checks if the
+ * hardware buffers are empty. However, such an API does not exist now,
+ * so we'll use the wait_ms() function for now.
+ */
+#define SERIAL_FLUSH_TIME_MS    20
+
 typedef enum {
     CMD_STATUS_CONTINUE,
     CMD_STATUS_ERROR
@@ -85,7 +101,7 @@ static cmd_status_t handle_command(const char *key, const char *value)
 
     if (strcmp(key, MSG_KEY_DEVICE_RESET) == 0 && strcmp(value, MSG_VALUE_DEVICE_RESET_NVIC) == 0) {
         greentea_send_kv(MSG_KEY_DEVICE_RESET, MSG_VALUE_DEVICE_RESET_ACK);
-        wait_ms(10); // Wait for the serial buffers to flush.
+        wait_ms(SERIAL_FLUSH_TIME_MS); // Wait for the serial buffers to flush.
         NVIC_SystemReset();
         TEST_ASSERT_MESSAGE(0, "NVIC_SystemReset did not reset the device as expected.");
         return CMD_STATUS_ERROR;
@@ -94,7 +110,7 @@ static cmd_status_t handle_command(const char *key, const char *value)
 #if DEVICE_WATCHDOG
     if (strcmp(key, MSG_KEY_DEVICE_RESET) == 0 && strcmp(value, MSG_VALUE_DEVICE_RESET_WATCHDOG) == 0) {
         greentea_send_kv(MSG_KEY_DEVICE_RESET, MSG_VALUE_DEVICE_RESET_ACK);
-        wait_ms(10); // Wait for the serial buffers to flush.
+        wait_ms(SERIAL_FLUSH_TIME_MS); // Wait for the serial buffers to flush.
         watchdog_config_t config = { .timeout_ms = WDG_TIMEOUT_MS };
         if (hal_watchdog_init(&config) != WATCHDOG_STATUS_OK) {
             TEST_ASSERT_MESSAGE(0, "hal_watchdog_init() error.");

TESTS/mbed_hal/watchdog/main.cpp

@@ -41,6 +41,22 @@
 #define MSG_KEY_START_CASE "start_case"
 #define MSG_KEY_DEVICE_RESET "reset_on_case_teardown"
 
+/* Flush serial buffer before deep sleep/reset
+ *
+ * Since deepsleep()/reset would shut down the UART peripheral, we wait for some time
+ * to allow for hardware serial buffers to completely flush.
+ *
+ * Take NUMAKER_PFM_NUC472 as an example:
+ * Its UART peripheral has 16-byte Tx FIFO. With baud rate set to 9600, flush
+ * Tx FIFO would take: 16 * 8 * 1000 / 9600 = 13.3 (ms). So set wait time to
+ * 20ms here for safe.
+ *
+ * This should be replaced with a better function that checks if the
+ * hardware buffers are empty. However, such an API does not exist now,
+ * so we'll use the wait_ms() function for now.
+ */
+#define SERIAL_FLUSH_TIME_MS    20
+
 int CASE_INDEX_START;
 int CASE_INDEX_CURRENT;
 
@@ -128,7 +144,7 @@ utest::v1::status_t case_teardown_sync_on_reset(const Case * const source, const
     }
     greentea_send_kv(MSG_KEY_DEVICE_RESET, CASE_INDEX_START + CASE_INDEX_CURRENT);
     utest_printf("The device will now restart.\n");
-    wait_ms(10); // Wait for the serial buffers to flush.
+    wait_ms(SERIAL_FLUSH_TIME_MS); // Wait for the serial buffers to flush.
     NVIC_SystemReset();
     return status; // Reset is instant so this line won't be reached.
 }

TESTS/mbed_hal/watchdog_reset/main.cpp

@@ -38,6 +38,22 @@
 #define MSG_KEY_START_CASE "start_case"
 #define MSG_KEY_DEVICE_RESET "dev_reset"
 
+/* Flush serial buffer before deep sleep/reset
+ *
+ * Since deepsleep()/reset would shut down the UART peripheral, we wait for some time
+ * to allow for hardware serial buffers to completely flush.
+ *
+ * Take NUMAKER_PFM_NUC472 as an example:
+ * Its UART peripheral has 16-byte Tx FIFO. With baud rate set to 9600, flush
+ * Tx FIFO would take: 16 * 8 * 1000 / 9600 = 13.3 (ms). So set wait time to
+ * 20ms here for safe.
+ *
+ * This should be replaced with a better function that checks if the
+ * hardware buffers are empty. However, such an API does not exist now,
+ * so we'll use the wait_ms() function for now.
+ */
+#define SERIAL_FLUSH_TIME_MS    20
+
 using utest::v1::Case;
 using utest::v1::Specification;
 using utest::v1::Harness;
@@ -149,7 +165,7 @@ void test_deepsleep_reset()
     }
     TEST_ASSERT_EQUAL(WATCHDOG_STATUS_OK, hal_watchdog_init(&config));
     lp_timeout.attach_us(mbed::callback(release_sem, &sem), 1000ULL * (TIMEOUT_MS + TIMEOUT_DELTA_MS));
-    wait_ms(10); // Wait for the serial buffers to flush.
+    wait_ms(SERIAL_FLUSH_TIME_MS); // Wait for the serial buffers to flush.
     if (!sleep_manager_can_deep_sleep()) {
         TEST_ASSERT_MESSAGE(0, "Deepsleep should be allowed.");
     }