Enable tickless for nRF52840

Author: nvlsianpu

targets/targets.json

@@ -3190,7 +3190,7 @@
     "MCU_NRF52840": {
         "inherits": ["Target"],
         "core": "Cortex-M4F",
-        "macros": ["TARGET_NRF52840", "BLE_STACK_SUPPORT_REQD", "SOFTDEVICE_PRESENT", "S140", "NRF_SD_BLE_API_VERSION=5", "NRF52840_XXAA", "NRF_DFU_SETTINGS_VERSION=1", "NRF_SD_BLE_API_VERSION=5", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\""],
+        "macros": ["TARGET_NRF52840", "BLE_STACK_SUPPORT_REQD", "SOFTDEVICE_PRESENT", "S140", "NRF_SD_BLE_API_VERSION=5", "NRF52840_XXAA", "NRF_DFU_SETTINGS_VERSION=1", "NRF_SD_BLE_API_VERSION=5", "CMSIS_VECTAB_VIRTUAL", "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"", "MBED_TICKLESS"],
         "device_has": ["STCLK_OFF_DURING_SLEEP"],
         "extra_labels": ["NORDIC", "MCU_NRF52840", "NRF5", "SDK13", "NRF52_COMMON"],
         "OUTPUT_EXT": "hex",