correct descriptions (#5849)

* correct descriptions

correct descriptions in ipc.c and timer.c
Co-authored-by: NStanley <stanleylwinn@gmail.com>

src/ipc.c

@@ -2230,7 +2230,14 @@ RTM_EXPORT(rt_mb_urgent);
  * @param    value is a flag that you will set for this mailbox's flag.
  *           You can set an mailbox flag, or you can set multiple flags through OR logic operations.
  *
- * @param    timeout is a timeout period (unit: an OS tick).
+ * @param    timeout is a timeout period (unit: an OS tick). If the mailbox object is not avaliable in the queue,
+ *           the thread will wait for the object in the queue up to the amount of time specified by this parameter.
+ *
+ *           NOTE:
+ *           If use Macro RT_WAITING_FOREVER to set this parameter, which means that when the
+ *           mailbox object is unavailable in the queue, the thread will be waiting forever.
+ *           If use macro RT_WAITING_NO to set this parameter, which means that this
+ *           function is non-blocking and will return immediately.
  *
  * @return   Return the operation status. When the return value is RT_EOK, the operation is successful.
  *           If the return value is any other values, it means that the mailbox release failed.

src/timer.c

 /*
- * Copyright (c) 2006-2021, RT-Thread Development Team
+ * Copyright (c) 2006-2022, RT-Thread Development Team
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -18,6 +18,7 @@
  *                             timeout function.
  * 2021-08-15     supperthomas add the comment
  * 2022-01-07     Gabriel      Moving __on_rt_xxxxx_hook to timer.c
+ * 2022-04-19     Stanley      Correct descriptions
  */
 
 #include <rtthread.h>
@@ -323,9 +324,18 @@ RTM_EXPORT(rt_timer_detach);
  *
  * @param time is timeout ticks of the timer
  *
- *             NOTE: The max timeout tick should be no more than (RT_TICK_MAX/2 - 1).
+ *        NOTE: The max timeout tick should be no more than (RT_TICK_MAX/2 - 1).
  *
- * @param flag is the flag of timer
+ * @param flag is the flag of timer. Timer will invoke the timeout function according to the selected values of flag, if one or more of the following flags is set.
+ *
+ *          RT_TIMER_FLAG_ONE_SHOT          One shot timing
+ *          RT_TIMER_FLAG_PERIODIC          Periodic timing
+ *
+ *          RT_TIMER_FLAG_HARD_TIMER        Hardware timer
+ *          RT_TIMER_FLAG_SOFT_TIMER        Software timer
+ *
+ *        NOTE:
+ *        You can use multiple values with "|" logical operator.  By default, system will use the RT_TIME_FLAG_HARD_TIMER.
  *
  * @return the created timer object
  */