STM8中断优先级不够怎么解决?

STM8L 中，中断优先级通过下面函数设置，但此处仅 ITC_PriorityLevel_1，ITC_PriorityLevel_2，ITC_PriorityLevel_3  总共才3个中断优先级可设置，若我超过3个中断，该怎么设置？

/**
  * @brief  Sets the software priority of the specified interrupt source.
  * @note   The modification of the software priority is only possible when
  *         the interrupts are disabled.
  * @note   The normal behavior is to disable the interrupt before calling
  *         this function, and re-enable it after.
  * @note   The priority level 0 cannot be set (see product specification
  *         for more details).
  * @param  IRQn : Specifies the peripheral interrupt source.
  * @param  ITC_PriorityLevel : Specifies the software priority value to set
  *          This parameter can be one of the following values:
  *            @arg ITC_PriorityLevel_0: Software priority level 0 (cannot be written)
  *            @arg ITC_PriorityLevel_1: Software priority level 1
  *            @arg ITC_PriorityLevel_2: Software priority level 2
  *            @arg ITC_PriorityLevel_3: Software priority level 3     
  * @retval None
  */
void ITC_SetSoftwarePriority(IRQn_TypeDef IRQn, ITC_PriorityLevel_TypeDef ITC_PriorityLevel)
{


}