From b3cea3f5a8b7e9de50c5a6f79933077b11448f33 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=9D=A8=E8=BF=9E=E9=92=8A?= <ylz0923@foxmail.com>
Date: Mon, 25 Mar 2019 10:35:32 +0800
Subject: [PATCH] Update drv_common.c

---
 bsp/stm32/libraries/HAL_Drivers/drv_common.c | 34 +++++---------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/bsp/stm32/libraries/HAL_Drivers/drv_common.c b/bsp/stm32/libraries/HAL_Drivers/drv_common.c
index 350c3fab4..9bffc026e 100644
--- a/bsp/stm32/libraries/HAL_Drivers/drv_common.c
+++ b/bsp/stm32/libraries/HAL_Drivers/drv_common.c
@@ -93,32 +93,14 @@ void _Error_Handler(char *s, int num)
  */
 void rt_hw_us_delay(rt_uint32_t us)
 {
-    rt_uint32_t ticks;
-    rt_uint32_t told, tnow, tcnt = 0;
-    rt_uint32_t reload = SysTick->LOAD;
-
-    ticks = us * reload / (1000000 / RT_TICK_PER_SECOND);
-    told = SysTick->VAL;
-    while (1)
-    {
-        tnow = SysTick->VAL;
-        if (tnow != told)
-        {
-            if (tnow < told)
-            {
-                tcnt += told - tnow;
-            }
-            else
-            {
-                tcnt += reload - tnow + told;
-            }
-            told = tnow;
-            if (tcnt >= ticks)
-            {
-                break;
-            }
-        }
-    }
+    rt_uint32_t start, now, delta, reload, us_tick;
+    start = SysTick->VAL;
+    reload = SysTick->LOAD;
+    us_tick = SystemCoreClock / 1000000UL;
+    do {
+        now = SysTick->VAL;
+        delta = start > now ? start - now : reload + start - now;
+    } while(delta < us_tick * us);
 }
 
 /**
-- 
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