Question
noise in dac using dma
Posted on December 20, 2011 at 10:52
Hello,
I can synthesize a waveform into a buffer, dma transfering it to dac. Result is ok but there's a noise that I can't remove. When the waveform is a 0 signal, the noise is still here. The noise has a frequency (~ dma interrupt freq) it seems to be square like, and seems to be louder when CPU is more used. Am I doing something wrong with dma or dac? The dac pin is directly connected to the amp input, I don't know if I should add some components? Do you know what can cause this noise? I made a simplified source code which can reproduce the error:#include ''stm32f10x.h''
#define DAC_DHR12RD_Address 0x40007420
/* Init Structure definition */
DAC_InitTypeDef DAC_InitStructure;
DMA_InitTypeDef DMA_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
NVIC_InitTypeDef NVIC_InitStructure;
uint16_t outbuf[32] = {
2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048,
2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048,
2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048,
2048, 2048, 2048, 2048, 2048, 2048, 2048, 2048};
char
compute_next_frame;
/* Private function prototypes -----------------------------------------------*/
void
RCC_Configuration(
void
);
void
GPIO_Configuration(
void
);
void
Delay(__IO uint32_t nCount);
int
main(
void
)
{
RCC_Configuration();
GPIO_Configuration();
/* TIM2 Configuration */
/* Time base configuration */
TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
TIM_TimeBaseStructure.TIM_Period = 24;
TIM_TimeBaseStructure.TIM_Prescaler = 30;
TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
/* TIM2 TRGO selection */
TIM_SelectOutputTrigger(TIM2, TIM_TRGOSource_Update);
/* DAC channel1 Configuration */
DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
DAC_Init(DAC_Channel_1, &DAC_InitStructure);
DMA_DeInit(DMA1_Channel3);
DMA_InitStructure.DMA_PeripheralBaseAddr = DAC_DHR12RD_Address;
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)&outbuf;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
DMA_InitStructure.DMA_BufferSize = 32;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel3, &DMA_InitStructure);
DMA_Cmd(DMA1_Channel3, ENABLE);
DMA_ITConfig(DMA1_Channel3, DMA_IT_TC, ENABLE);
NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
//HIGHEST_PRIORITY;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init( &NVIC_InitStructure );
DAC_Cmd(DAC_Channel_1, ENABLE);
DAC_DMACmd(DAC_Channel_1, ENABLE);
/* TIM2 enable counter */
TIM_Cmd(TIM2, ENABLE);
compute_next_frame = 0;
while
(1)
{
while
(!compute_next_frame);
// compute the next frame
// simulate cpu load
// when this block is off there's some noise but less
int
i, j;
for
(i=1;i<2000;i++)
j = 4984131/i;
compute_next_frame=0;
}
}
void
RCC_Configuration(
void
)
{
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
}
void
GPIO_Configuration(
void
)
{
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
GPIO_Init(GPIOA, &GPIO_InitStructure);
}
// function called in stm32f10x_it.c by DMA1_Channel3_IRQHandler
void
dma_it(){
if
(DMA_GetITStatus(DMA1_IT_TC3)) {
int
i;
// simulating square signal (1048 / 3048) or 0 signal (2048 / 2048)
if
(outbuf[0]==3048)
for
(i=0; i<32; i++)
outbuf[i] = 2048;
//1048;
else
for
(i=0; i<32; i++)
outbuf[i] = 2048;
//3048;
compute_next_frame = 1;
DMA_ClearITPendingBit(DMA1_IT_GL3);
}
}