8位基本定时器（TIM4）

简介：该定时器由一个带可编程预分频器的8位自动重载的向上计数器所组成，它可以用来作为时基发生器，具有溢出中断功能。

主要功能：

（1）8位向上计数的自动重载计数器；

（2）3位可编程的预分配器（可在运行中修改），提供1、2、4、8、16、32、64、128这8种分频比例；

（3）中断产生：更新中断（溢出，计数器初始化）。

代码实现：

 /* Includes ------------------------------------------------------------------*/
 #include "stm8s.h"

 /* Private define ------------------------------------------------------------*/
 #define TIM4_PERIOD       124
 /* Private variables ---------------------------------------------------------*/
 __IO uint32_t TimingDelay = ;
 /* Private function prototypes -----------------------------------------------*/
 void Delay(__IO uint32_t nTime);
 void TimingDelay_Decrement(void);
 static void TIM4_Config(void);

 /**
   * @brief  Main program.
   * @param  None
   * @retval None
   */
 void main(void)
 {
   /* TIM4 configuration -----------------------------------------*/
   TIM4_Config();    

   /* Insert 50 ms delay */
   Delay();
   }
 }

 /**
   * @brief  Configure TIM4 to generate an update interrupt each 1ms
   * @param  None
   * @retval None
   */
 static void TIM4_Config(void)
 {
   /* TIM4 configuration:
    - TIM4CLK is set to 16 MHz, the TIM4 Prescaler is equal to 128 so the TIM1 counter
    clock used is 16 MHz / 128 = 125 000 Hz
   - With 125 000 Hz we can generate time base:
       max time base is 2.048 ms if TIM4_PERIOD = 255 --> (255 + 1) / 125000 = 2.048 ms
       min time base is 0.016 ms if TIM4_PERIOD = 1   --> (  1 + 1) / 125000 = 0.016 ms
   - In this example we need to generate a time base equal to 1 ms
    so TIM4_PERIOD = (0.001 * 125000 - 1) = 124 */

   /* Time base configuration */
   TIM4_TimeBaseInit(TIM4_PRESCALER_128, TIM4_PERIOD);
   /* Clear TIM4 update flag */
   TIM4_ClearFlag(TIM4_FLAG_UPDATE);
   /* Enable update interrupt */
   TIM4_ITConfig(TIM4_IT_UPDATE, ENABLE);

   /* enable interrupts */
   enableInterrupts();

   /* Enable TIM4 */
   TIM4_Cmd(ENABLE);
 }

 /**
   * @brief  Inserts a delay time.
   * @param  nTime: specifies the delay time length, in milliseconds.
   * @retval None
   */
 void Delay(__IO uint32_t nTime)
 {
   TimingDelay = nTime;

   while (TimingDelay != );
 }

 /**
   * @brief  Decrements the TimingDelay variable.
   * @param  None
   * @retval None
   */
 void TimingDelay_Decrement(void)
 {
   if (TimingDelay != 0x00)
   {
     TimingDelay--;
   }
 }

TIM4