为什么配置TIM11作为系统时基的时候会出现__NVIC_PRIO_BITS

回想起当初学freertos的时候，某个中断优先级以下的任务是不能被freertos管理的（好像是全是抢占优先级，0子优先级的设置）。当初还不是非常了解。只知道管理不了

HAL_StatusTypeDef HAL_InitTick(uint32_t TickPriority)
{
  RCC_ClkInitTypeDef    clkconfig;
  uint32_t              uwTimclock = 0U;

  uint32_t              uwPrescalerValue = 0U;
  uint32_t              pFLatency;
  HAL_StatusTypeDef     status;

  /* Enable TIM11 clock */
  __HAL_RCC_TIM11_CLK_ENABLE();
  /* Get clock configuration */
  HAL_RCC_GetClockConfig(&clkconfig, &pFLatency);
  /* Compute TIM11 clock */
      uwTimclock = HAL_RCC_GetPCLK2Freq();

  /* Compute the prescaler value to have TIM11 counter clock equal  to 1MHz */
  uwPrescalerValue = (uint32_t) ((uwTimclock / 1000000U) - 1U);

  /* Initialize TIM11 */
  htim11.Instance = TIM11;

  /* Initialize TIMx peripheral as follow:

  + Period = [(TIM11CLK/1000) - 1]. to have a (1/1000) s time base.
  + Prescaler = (uwTimclock/1000000 - 1) to have a 1MHz counter clock.
  + ClockDivision = 0
  + Counter direction = Up
  */
  htim11.Init.Period = (1000000U / 1000U) - 1U;
  htim11.Init.Prescaler = uwPrescalerValue;
  htim11.Init.ClockDivision = 0;
  htim11.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim11.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;

  status = HAL_TIM_Base_Init(&htim11);
  if (status == HAL_OK)
  {
    /* Start the TIM time Base generation in interrupt mode */
    status = HAL_TIM_Base_Start_IT(&htim11);
    if (status == HAL_OK)
    {
    /* Enable the TIM11 global Interrupt */
        HAL_NVIC_EnableIRQ(TIM1_TRG_COM_TIM11_IRQn);//如果启动成功，启用 TIM11 的全局中断
      /* Configure the SysTick IRQ priority */
      if (TickPriority < (1UL << __NVIC_PRIO_BITS))//TI Stellaris Cortex-M3 和 Cortex-M4 微控制器使用优先级配置寄存器的 3 个位，能提供 8 级优先级
      {
        /* Configure the TIM IRQ priority */
        HAL_NVIC_SetPriority(TIM1_TRG_COM_TIM11_IRQn, TickPriority, 0U);
        uwTickPrio = TickPriority;
      }
      else
      {
        status = HAL_ERROR;
      }
    }
  }

 /* Return function status */
  return status;
}

今天在看cubemx生成的代码里看到了这个配置

 if (TickPriority < (1UL << __NVIC_PRIO_BITS))//TI Stellaris Cortex-M3 和 Cortex-M4 微控制器使用优先级配置寄存器的 3 个位，能提供 8 级优先级
      {
        /* Configure the TIM IRQ priority */
        HAL_NVIC_SetPriority(TIM1_TRG_COM_TIM11_IRQn, TickPriority, 0U);
        uwTickPrio = TickPriority;
      }

原因大致就是使用优先级 1<<3 = 0x1000 = 8 配置寄存器的 3 个位提供 8 级优先级

而这些详细的与freertos之间联系可以查阅下文

 FreeRTOS 之七 Cortex-M 中的中断优先级设置_cortex中断优先级分组-优快云博客