有没有人知道，STM32 DAC 在DMA模式下启动的每次时间是否固定？

dtszcr

 我最近用STM32F103VCT6 的DAC产生两路同频正弦波，通过定时器1延时控制两个波形的相位。但是不知道为什么调节的时候，相位间隔并不是以定时器的分辨率步进，要调节好几个值相位才能动一下，而且相位变动值都不固定。
程序是每次步进一下，重新设置DMA 和DAC ，然后先打开第一路DAC的时钟TIMx1，然后打开定时器，定时中断到就打开第二路的时钟TIMx2，不知道是不是我的程序问题，还是STM32本身启动DMA DAC时间就不确定。
可以确定定时器是没问题，我用IO口翻转做个实验，可以实现很精确的步进。
DMA 和DAC 配置程序如下
 NVIC_SETFAULTMASK();  //关闭总中断
  SysTick_ITConfig(DISABLE);
 TIM_Cmd(TIM2, DISABLE);  /* TIM2 enable counter */
  TIM_Cmd(TIM4, DISABLE);  /* TIM4 enable counter */
  
  DMA_Cmd(DMA2_Channel3, DISABLE);  /* Enable DMA1 Channel3 */ 
  DAC_Cmd(DAC_Channel_1, DISABLE);  /* Enable DAC Channel1 */ 
  DAC_DMACmd(DAC_Channel_1,DISABLE);  /* Enable DMA for DAC Channel1 */
  
  DMA_Cmd(DMA2_Channel4, DISABLE);  /* Enable DMA2 Channel3 */ 
  DAC_Cmd(DAC_Channel_2, DISABLE);  /* Enable DAC Channel2 */ 
  DAC_DMACmd(DAC_Channel_2, DISABLE);  /* Enable DMA for DAC Channel2 */
  TIM_DeInit(TIM2);        /* Resets the TIM2 */
  TIM_DeInit(TIM4);  /* Resets the TIM4 */
  
  TIM_PrescalerConfig(TIM2, 0x00, TIM_PSCReloadMode_Update); /* TIM2 Configuration */
  TIM_SetAutoreload(TIM2, T); //设置定时器2自动重装  
  TIM_SelectOutputTrigger(TIM2, TIM_TRGOSource_Update);        /* TIM2 TRGO selection */


  /* DAC channel1 Configuration */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
  DAC_Init(DAC_Channel_1, &DAC_InitStructure); 


  /* DMA2 channel3 configuration */ 
  DMA_DeInit(DMA2_Channel3);
  DMA_InitStructure.DMA_PeripheralBaseAddr = DAC_DHR8R1_Address;
  DMA_InitStructure.DMA_MemoryBaseAddr = (u32)&Escalator8bit1;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
  DMA_InitStructure.DMA_BufferSize = 256;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
  DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
  DMA_InitStructure.DMA_Priority = DMA_Priority_High;
  DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
  DMA_Init(DMA2_Channel3, &DMA_InitStructure);


 
  DMA_Cmd(DMA2_Channel3, ENABLE);  /* Enable DMA1 Channel3 */ 
  DAC_Cmd(DAC_Channel_1, ENABLE);  /* Enable DAC Channel1 */ 
  DAC_DMACmd(DAC_Channel_1, ENABLE);  /* Enable DMA for DAC Channel1 */
  //TIM_Cmd(TIM2, ENABLE);  /* TIM2 enable counter */




  TIM_PrescalerConfig(TIM4, 0x00, TIM_PSCReloadMode_Update); /* TIM4 Configuration */
  TIM_SetAutoreload(TIM4, T); //设置定时器4自动重装  
  TIM_SelectOutputTrigger(TIM4, TIM_TRGOSource_Update);        /* TIM4 TRGO selection */


    /* DAC channel2 Configuration*/ 
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T4_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);


  /* DMA2 channel4 configuration */
  DMA_DeInit(DMA2_Channel4);
  DMA_InitStructure.DMA_PeripheralBaseAddr = DAC_DHR8R2_Address;
  DMA_InitStructure.DMA_MemoryBaseAddr = (u32)&Escalator8bit2;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
  DMA_InitStructure.DMA_BufferSize = 256;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
  DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
  DMA_InitStructure.DMA_Priority = DMA_Priority_High;
  DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
  DMA_Init(DMA2_Channel4, &DMA_InitStructure);         


  DMA_Cmd(DMA2_Channel4, ENABLE);  /* Enable DMA2 Channel3 */ 
  DAC_Cmd(DAC_Channel_2, ENABLE);  /* Enable DAC Channel2 */ 
  DAC_DMACmd(DAC_Channel_2, ENABLE);  /* Enable DMA for DAC Channel2 */


  
  TIM_Cmd(TIM2, ENABLE);  /* TIM2 enable counter */ //  此次打开第一路DAC 
  NVIC_RESETFAULTMASK();//开放总中断
  Time1_Configuration();   //配置定时器1，用来延时产生第二路DAC，在定时器1中断中打开第二路DAC

 
定时器1中断中启动第二路DAC的程序如下
void TIM1_UP_IRQHandler(void)
{
TIM_ClearITPendingBit(TIM1, TIM_IT_Update);
TIM_ITConfig(TIM1, TIM_IT_Update, DISABLE );                                          
TIM_Cmd(TIM1, DISABLE);
 TIM_Cmd(TIM4, ENABLE);  /* TIM4 enable counter */  //此处  打开第二路DAC
SysTick_ITConfig(ENABLE); 
}