bsp/stm32f10x/touch: return early when lost the position

Check whether finger is still on the screen. If not, we couldn't determine where the user has touched. It's better to return early rather than give garbage values.

A more sensitive solution might be caculate the position once the interrupt occured. But it's not anti-shake friendly.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1789 bbd45198-f89e-11dd-88c7-29a3b14d5316

bsp/stm32f10x/touch.c

@@ -196,6 +196,10 @@ void touch_timeout(void* parameter)
         rt_uint32_t y;
     } touch_previous;
 
+    /* touch time is too short and we lost the position already. */
+    if ((!touch_down) && GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_0) != 0)
+        return;
+
     if (GPIO_ReadInputDataBit(GPIOB,GPIO_Pin_1) != 0)
     {
         int tmer = RT_TICK_PER_SECOND/8 ;