From 4789bf619582970f35a5f6e90a4369b701776dc2 Mon Sep 17 00:00:00 2001
From: AlexShi <shiweining123@163.com>
Date: Thu, 25 Mar 2021 09:48:53 +0800
Subject: [PATCH] update
 rt-thread-version/rt-thread-standard/programming-manual/timer/timer.md.

---
 .../rt-thread-standard/programming-manual/timer/timer.md  | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/rt-thread-version/rt-thread-standard/programming-manual/timer/timer.md b/rt-thread-version/rt-thread-standard/programming-manual/timer/timer.md
index 4ce502c..f925f03 100644
--- a/rt-thread-version/rt-thread-standard/programming-manual/timer/timer.md
+++ b/rt-thread-version/rt-thread-standard/programming-manual/timer/timer.md
@@ -512,13 +512,15 @@ RT-Thread 定时器的最小精度是由系统时钟节拍所决定的（1 OS Ti
 #include <board.h>
 void rt_hw_us_delay(rt_uint32_t us)
 {
-    rt_uint32_t delta;
+    rt_uint32_t tstart;
     /* 获得延时经过的 tick 数 */
     us = us * (SysTick->LOAD/(1000000/RT_TICK_PER_SECOND));
     /* 获得当前时间 */
-    delta = SysTick->VAL;
+    tstart = SysTick->VAL;
+    /* 判断是否会溢出 */
+    if (tstart < us) tstart += SysTick->LOAD;
     /* 循环获得当前时间，直到达到指定的时间后退出循环 */
-    while (delta - SysTick->VAL< us);
+    while (tstart - SysTick->VAL < us);
 }
 
 ```
-- 
Gitee