DAC+DMA+TIMER输出正玄波通道1一直是高电平

问题描述：我用 STM32f207的PA4(DAC通道1)、PA5(DAC通道2)输出正玄波和余弦波，利用了DMA和 tiM2和TIM6分别做触发，TIM2触发DMA1_Stream5，TIM6触发DMA1_Stream6，PA4输出了正弦波，PA5输出了余弦波， TIM2->ARR = 20; TIM6->ARR = 20;输出频率相同，看不出问题，可是问题出在哪里呢？问题在于，当ARR的值小于15的时候，比如 TIM2->ARR = 14;
TIM6->ARR = 14；
问题来了，通道1一直是高电平，通道输出余弦波正常。
于是改变用TIM2触发DMA1_Stream6，TIM6触发DMA1_Stream5，ARR都为14（低于15都一样）; 同样还是通道一有同样的问题，二通道2却正常输出了波形。于是我想跟TIM没有关系，后来也尝试改变波形数据，发现也不是波形数据的问题。不知道是否有大神帮我分析一下这个问题是怎么回事。我用的是keil工具。数据是用EXCEl计算出来的，应该是没有问题的。代码如下：


#include "stm32f2xx_dac.h"
#include "stm32f2xx_dma.h"
#include "stm32f2xx.h"


#define DAC1_DMA_ADDR 0x40007408 // DAC通道1地址
#define DAC2_DMA_ADDR 0x40007414 // DAC通道2地址



uc32 DAC_sinTAB[]={
2000 ,2098 ,2196 ,2293 ,2390 ,2486 ,2581 ,2674 ,
2765 ,2855 ,2943 ,3028 ,3111 ,3191 ,3269 ,3343 ,
3414 ,3482 ,3546 ,3606 ,3663 ,3715 ,3764 ,3808 ,
3848 ,3883 ,3914 ,3940 ,3962 ,3978 ,3990 ,3998 ,
4000 ,3998 ,3990 ,3978 ,3962 ,3940 ,3914 ,3883 ,
3848 ,3808 ,3764 ,3715 ,3663 ,3606 ,3546 ,3482 ,
3414 ,3343 ,3269 ,3191 ,3111 ,3028 ,2943 ,2855 ,
2765 ,2674 ,2581 ,2486 ,2390 ,2293 ,2196 ,2098 ,
2000 ,1902 ,1804 ,1707 ,1610 ,1514 ,1419 ,1326 ,
1235 ,1145 ,1057 ,972 ,889 ,809 ,731 ,657 ,
586 ,518 ,454 ,394 ,337 ,285 ,236 ,192 ,
152 ,117 , 86 , 60 , 38 , 22 , 10 , 2 ,
0 , 2 , 10 , 22 , 38 , 60 , 86 ,117 ,
152 ,192 ,236 ,285 ,337 ,394 ,454 ,518 ,
586 ,657 ,731 ,809 ,889 ,972 ,1057 ,1145 ,
1235 ,1326 ,1419 ,1514 ,1610 ,1707 ,1804 ,1902
};



uc32 DAC_cosTAB[] = {
4000 ,3998 ,3990 ,3978 ,3962 ,3940 ,3914 ,3883 ,
3848 ,3808 ,3764 ,3715 ,3663 ,3606 ,3546 ,3482 ,
3414 ,3343 ,3269 ,3191 ,3111 ,3028 ,2943 ,2855 ,
2765 ,2674 ,2581 ,2486 ,2390 ,2293 ,2196 ,2098 ,
2000 ,1902 ,1804 ,1707 ,1610 ,1514 ,1419 ,1326 ,
1235 ,1145 ,1057 ,972 ,889 , 809 ,731 ,657 ,
586 ,518 ,454 ,394 ,337 ,285 , 236 ,192 ,
152 ,117 , 86 , 60 , 38 , 22 , 10 ,2 ,
0 , 2 , 10 , 22 , 38 , 60 , 86 ,117 ,
152 ,192 ,236 ,285 ,337 ,394 ,454 ,518 ,
586 ,657 ,731 ,809 ,889 ,972 ,1057 ,1145 ,
1235 ,1326 ,1419 ,1514 ,1610 ,1707 ,1804 ,1902 ,
2000 ,2098 ,2196 ,2293 ,2390 ,2486 ,2581 ,2674 ,
2765 ,2855 ,2943 ,3028 ,3111 ,3191 ,3269 ,3343 ,
3414 ,3482 ,3546 ,3606 ,3663 ,3715 ,3764 ,3808 ,
3848 ,3883 ,3914 ,3940 ,3962 ,3978 ,3990 ,3998
};



void TIM_Int_Init(u16 arr,u16 psc)
{
RCC->APB1ENR|=1<<0; //TIM2时钟使能
TIM2->ARR=arr;
TIM2->PSC=psc;
TIM2->CR1|=1<<7;
TIM2->CR2 |=0x2<<4; //TIMER更新作为TRGO源
TIM2->CR1 |=TIM_CR1_CEN;

TIM6->ARR=arr; //TIM6的时钟在前面系统初始化的时候已经开启了，这里不在重复开启，不影响问题的本质
TIM6->PSC=psc;
TIM6->CR1|=1<<7;
TIM6->CR2 |=0x2<<4;
TIM6->CR1 |=TIM_CR1_CEN;

}


void DAC_DMA_init(void)
{
DMA_InitTypeDef DMA_InitStructure;

DMA_DeInit(DMA1_Stream5);
DMA_InitStructure.DMA_Channel = DMA_Channel_7;
DMA_InitStructure.DMA_PeripheralBaseAddr = DAC1_DMA_ADDR;
DMA_InitStructure.DMA_Memory0BaseAddr = (u32)DAC_cosTAB;//

DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;
DMA_InitStructure.DMA_BufferSize =128;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;//
DMA_InitStructure.DMA_MemoryDataSize = DMA_PeripheralDataSize_Word;//
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;// ;
DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;

DMA_InitStructure.DMA_FIFOMode=DMA_FIFOMode_Disable;
DMA_InitStructure.DMA_FIFOThreshold=DMA_FIFOThreshold_1QuarterFull;
DMA_InitStructure.DMA_MemoryBurst=DMA_MemoryBurst_Single;
DMA_InitStructure.DMA_PeripheralBurst=DMA_PeripheralBurst_Single;

DMA_Init(DMA1_Stream5, &DMA_InitStructure);
DMA_Cmd(DMA1_Stream5, ENABLE);

///////////////////////////////////////////////////////////////////////////////////////////////////////

DMA_DeInit(DMA1_Stream6);
DMA_InitStructure.DMA_Channel = DMA_Channel_7;
DMA_InitStructure.DMA_PeripheralBaseAddr = DAC2_DMA_ADDR;
DMA_InitStructure.DMA_Memory0BaseAddr = (u32)DAC_sinTAB;//

DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;
DMA_InitStructure.DMA_BufferSize =128;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word;//
DMA_InitStructure.DMA_MemoryDataSize = DMA_PeripheralDataSize_Word;//
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;// ;
DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;

DMA_InitStructure.DMA_FIFOMode=DMA_FIFOMode_Disable;
DMA_InitStructure.DMA_FIFOThreshold=DMA_FIFOThreshold_1QuarterFull;
DMA_InitStructure.DMA_MemoryBurst=DMA_MemoryBurst_Single;
DMA_InitStructure.DMA_PeripheralBurst=DMA_PeripheralBurst_Single;

DMA_Init(DMA1_Stream6, &DMA_InitStructure);
DMA_Cmd(DMA1_Stream6, ENABLE);



}


void Dac1_Init(void)
{
DAC_InitTypeDef DAC_InitStructure;
RCC->APB1ENR|=1<<29; // DAC时钟开启
DAC_DeInit();

DAC_StructInit(&DAC_InitStructure);
DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;//
DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable; //
DAC_InitStructure.DAC_Trigger = DAC_Trigger_T6_TRGO;//

DAC_Init(DAC_Channel_1, &DAC_InitStructure); //
DAC_Cmd(DAC_Channel_1, ENABLE); //
DAC_DMACmd(DAC_Channel_1, ENABLE); //

DAC_StructInit(&DAC_InitStructure);
DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;//
DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable; //
DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;//DAC

DAC_Init(DAC_Channel_2, &DAC_InitStructure); //
DAC_Cmd(DAC_Channel_2, ENABLE); //
DAC_DMACmd(DAC_Channel_2, ENABLE); //

DAC_DMA_init();

TIM_Int_Init(100,0);


}

void DDS_Output_Wave( u16 frq )
{
TIM2->ARR = frq;
TIM6->ARR = frq;
}




说明：在初始化的时候，只要调用Dac1_Init（）就OK了，想要改变波形频率，只要调用 DDS_Output_Wave( u16 frq )函数，改变frq的值就OK 了。


问题再重申一下，就是当frq的值低于15的时候，就出问题了，通道一只有高电平，没有波形输出，但是通道2正常。请大神指点帮助。谢谢