执行路径如下:
init_sequence_r[]
-> initr_watchdog()
-> wdt_start(): include/wdt.h (default 60 second)
-> INIT_FUNC_WATCHDOG_RESET (common/board_r.c)
-> init_func_watchdog_reset()
-> WATCHDOG_RESET() -> watchdog_reset() : drivers/watchdog/wdt-uclass.c
-> get_timer()
-> wdt_reset()
-> ops->reset()
->
-> WATCHDOG_RESET(): drivers/serial/serial-uclass.c
-> xxxxx_tstc(): (串口驱动里会调用此接口,如使用的pl010串口，那么源码在driver/serial/serial_p101x.c中)