C++ DAC_Init函数代码示例

/**
  * @brief  Configures DAC channel 1 and channel 2
  * @param  None
  * @retval None
  */
void DAC_Config(void)
{
  /* Enable GPIOA Periph clock --------------------------------------*/
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
  /* Configure PA.04 (DAC_OUT1), PA.05 (DAC_OUT2) as analog */
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_4 | GPIO_Pin_5;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* DAC Periph clock enable */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

  /* DAC init struct configuration */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;

  /* DAC channel1 Configuration */
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);

  /* DAC channel2 Configuration */
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);

  /* Enable DAC Channel1: Once the DAC channel1 is enabled, PA.04 is 
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_1, ENABLE);
  
  /* Enable DAC Channel2: Once the DAC channel2 is enabled, PA.05 is 
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_2, ENABLE);

  /* Enable DMA for DAC Channel2 */
  DAC_DMACmd(DAC_Channel_2, ENABLE);
}

void setup_dac(){

#if isUsingDevBoard

	//Setup GPIO
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

	DAC_InitTypeDef DAC_InitStructure;

	/* DAC channel1 Configuration */
	DAC_InitStructure.DAC_Trigger = DAC_Trigger_None;
	DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
	DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bits10_0;
	DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
	DAC_Init(DAC_Channel_1, &DAC_InitStructure);
	DAC_Init(DAC_Channel_2, &DAC_InitStructure);

	/* Enable DAC Channel1 */
	DAC_Cmd(DAC_Channel_1, ENABLE);
	DAC_Cmd(DAC_Channel_2, ENABLE);

	/* Set DAC Channel1 DHR12L register */
	DAC_SetChannel1Data(DAC_Align_8b_R, 0x0000);
	DAC_SetChannel2Data(DAC_Align_8b_R, 0x0000);



#else

#endif

}

/**
  * @brief  DAC Channel2 Triangle and Channel1 Noise Configuration
  * @param  None
  * @retval None
  */
static void DAC_Noise_TriangleConfig(void)
{
  /* DAC channel2 Configuration */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_Triangle;
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_1023;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);
  
  /* Enable DAC Channel2 */
  DAC_Cmd(DAC_Channel_2, ENABLE);
  
  /* Set DAC channel2 DHR12RD register */
  DAC_SetChannel2Data(DAC_Align_12b_R, 0x100);
  
   /* DAC channel1 Configuration */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_Noise;
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bits10_0;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);
  
  /* Enable DAC Channel1 */
  DAC_Cmd(DAC_Channel_1, ENABLE);
  
  /* Set DAC Channel1 DHR12L register */
  DAC_SetChannel1Data(DAC_Align_12b_L, 0x7FF0);
}

/**
  * @brief  Configures the DAC.
  * @param  None
  * @retval None
  */
void DAC_Configuration(void)
{
    DAC_InitPara  DAC_InitStructure;

    RCC_APB1PeriphClock_Enable(RCC_APB1PERIPH_DAC, ENABLE);
    /* DAC channel1 Configuration */
    DAC_InitStructure.DAC_Trigger = DAC_TRIGGER_T2_TRIG;
    DAC_InitStructure.DAC_WaveType = DAC_WAVEGENE_NOISE;
    DAC_InitStructure.DAC_LFSRNoise_AmplitudeTriangle = DAC_LFSR_BITS9_0;
    DAC_InitStructure.DAC_OutputBuffer = DAC_OUTPUTBUFFER_DISABLE;
    DAC_Init(DAC_CHANNEL_1, &DAC_InitStructure);

   /* DAC channel2 Configuration */
    DAC_InitStructure.DAC_Trigger = DAC_TRIGGER_T3_TRIG;
    DAC_InitStructure.DAC_LFSRNoise_AmplitudeTriangle = DAC_LFSR_BITS10_0;
    DAC_Init(DAC_CHANNEL_2, &DAC_InitStructure);
    /* Enable DAC Channel1: Once the DAC channel1 is enabled, PA.04 is 
    automatically connected to the DAC converter. */
    DAC_Enable(DAC_CHANNEL_1, ENABLE);
    /* Enable DAC Channel2: Once the DAC channel2 is enabled, PA.05 is 
    automatically connected to the DAC converter. */
    DAC_Enable(DAC_CHANNEL_2, ENABLE);        
    /* Set DAC dual channel DHR12RD register */
    DAC_SetDualChannelData(DAC_ALIGN_12B_R, 0x7F0, 0x7F0);
}

void DAC_ConfigurationInit()
{
	DAC_InitTypeDef DAC_InitStruct;
	GPIO_InitTypeDef GPIO_InitStruct;

	RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOA, ENABLE );
	RCC_APB1PeriphClockCmd( RCC_APB1Periph_DAC, ENABLE );        

	GPIO_InitStruct.GPIO_Pin = GPIO_Pin_4;
	GPIO_InitStruct.GPIO_Mode = GPIO_Mode_Out_PP;
	GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init( GPIOA, &GPIO_InitStruct );

	GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5;
	GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AIN;
	GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init( GPIOA, &GPIO_InitStruct );

	DAC_InitStruct.DAC_Trigger = DAC_Trigger_Software;
	DAC_InitStruct.DAC_WaveGeneration = DAC_WaveGeneration_None;
	DAC_InitStruct.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bit0;
	DAC_InitStruct.DAC_OutputBuffer = DAC_OutputBuffer_Disable;

	DAC_Init( DAC_Channel_1, &DAC_InitStruct );
	DAC_Init( DAC_Channel_2, &DAC_InitStruct );

	DAC_Cmd( DAC_Channel_1, ENABLE );
	DAC_Cmd( DAC_Channel_2, ENABLE );

	DAC_SetChannel1Data( DAC_Align_12b_R, 0X0fFF);
	DAC_SoftwareTriggerCmd( DAC_Channel_1, ENABLE );

	DAC_SetChannel1Data( DAC_Align_12b_R, 0X03FF);
	DAC_SoftwareTriggerCmd( DAC_Channel_2, ENABLE );
}

void TM_DAC_Init(TM_DAC_Channel_t DACx) {
	DAC_InitTypeDef DAC_InitStruct;
	uint16_t GPIO_Pin;
	
	/* Select proper GPIO pin */
	if (DACx == TM_DAC1) {
		GPIO_Pin = GPIO_PIN_4;
	} else {
		GPIO_Pin = GPIO_PIN_5;
	}
	
	/* Initialize proper GPIO pin */
	TM_GPIO_Init(GPIOA, GPIO_Pin, TM_GPIO_Mode_AN, TM_GPIO_OType_PP, TM_GPIO_PuPd_NOPULL, TM_GPIO_Speed_Fast);

	/* Enable DAC clock */
	RCC->APB1ENR |= RCC_APB1ENR_DACEN;
	
	/* Set DAC options */
	DAC_InitStruct.DAC_Trigger = DAC_Trigger_None;
	DAC_InitStruct.DAC_WaveGeneration = DAC_WaveGeneration_None;
	DAC_InitStruct.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
	
	/* Init and enable proper DAC */
	if (DACx == TM_DAC1) {
		DAC_Init(DAC_Channel_1, &DAC_InitStruct);
		/* Enable DAC channel 1 */
		DAC->CR |= DAC_CR_EN1;
	} else {
		DAC_Init(DAC_Channel_2, &DAC_InitStruct);
		/* Enable DAC channel 2 */
		DAC->CR |= DAC_CR_EN2;
	}
}

void init_DACs(void)
{
    // Now to output to some pin ofcourse, PA4 for example (routed to audio PA)
    //  Enable clock to GPIOA
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    // Init the pins
    GPIO_InitTypeDef GPIOInit = {0, };
    GPIOInit.GPIO_Pin	= GPIO_Pin_4 | GPIO_Pin_5; // PA4
    GPIOInit.GPIO_Mode	= GPIO_Mode_AN; // Analog function
    GPIOInit.GPIO_PuPd	= GPIO_PuPd_NOPULL;
    
    GPIO_Init(GPIOA, &GPIOInit);

    // Enable the clock to the DAC
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
    DAC_InitTypeDef dacInit;
    memset( (void *)&dacInit, 0, sizeof(DAC_InitTypeDef) );
    dacInit.DAC_Trigger = DAC_Trigger_None;
    dacInit.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
    
    DAC_Init(DAC_Channel_1, &dacInit);
    DAC_Cmd(DAC_Channel_1, ENABLE);

    DAC_Init(DAC_Channel_2, &dacInit);
    DAC_Cmd(DAC_Channel_2, ENABLE);
}

/**
  * @brief   Main program.
  * @param  None
  * @retval None
  */
int main(void)
{
  /*!< At this stage the microcontroller clock setting is already configured,
       this is done through SystemInit() function which is called from startup
       file (startup_stm32f10x_xx.s) before to branch to application main.
       To reconfigure the default setting of SystemInit() function, refer to
       system_stm32f10x.c file
     */

  /* System Clocks Configuration */
  RCC_Configuration();

  /* Once the DAC channel is enabled, the corresponding GPIO pin is automatically
     connected to the DAC converter. In order to avoid parasitic consumption,
     the GPIO pin should be configured in analog */
  GPIO_Configuration();

  /* TIM2 Configuration */
  TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
  TIM_TimeBaseStructure.TIM_Period = 0xF;
  TIM_TimeBaseStructure.TIM_Prescaler = 0xF;
  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_Triangle;
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_2047;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);

  /* DAC channel2 Configuration */
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_1023;
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);

  /* Enable DAC Channel1: Once the DAC channel1 is enabled, PA.04 is
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_1, ENABLE);

  /* Enable DAC Channel2: Once the DAC channel2 is enabled, PA.05 is
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_2, ENABLE);

  /* Set DAC dual channel DHR12RD register */
  DAC_SetDualChannelData(DAC_Align_12b_R, 0x100, 0x100);

  /* TIM2 enable counter */
  TIM_Cmd(TIM2, ENABLE);

  while (1)
  {
  }
}

void SOUNDInitDAC(uint32_t sampleRate)
{
	GPIO_InitTypeDef GPIO_InitStructure;
	DAC_InitTypeDef DAC_InitStructure;

//	CS43L22Init();

	RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC | RCC_APB1Periph_TIM6, ENABLE);
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1 | RCC_AHB1Periph_GPIOA | RCC_AHB1Periph_GPIOC, ENABLE);

	// PC5 MAX4410 Audio Amp Shutdown
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
	GPIO_Init(GPIOC, &GPIO_InitStructure);	// 初期化関数を読み出します。

	AUDIO_OUT_SHUTDOWN;

	// PA4 PA5 DAC_OUT1 DAC_OUT2
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5;
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
	GPIO_Init(GPIOA, &GPIO_InitStructure);	// 初期化関数を読み出します。

	DAC_DeInit();
	DAC_InitStructure.DAC_Trigger = DAC_Trigger_T6_TRGO;
	DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
	DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bit0;
	DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
	DAC_Init(DAC_Channel_1, &DAC_InitStructure);
	DAC_Init(DAC_Channel_2, &DAC_InitStructure);

	DAC_DMACmd(DAC_Channel_1, ENABLE);
	DAC_DMACmd(DAC_Channel_2, ENABLE);

	DAC_Cmd(DAC_Channel_1, ENABLE);
	DAC_Cmd(DAC_Channel_2, ENABLE);

	TIM6->ARR = ((SystemCoreClock / 4) * 2) / sampleRate - 1;
	TIM6->PSC = 0;

	TIM6->CR1 |= _BV(7);
	TIM6->CR2 |= TIM_TRGOSource_Update;
	TIM6->DIER |= TIM_DMA_Update | _BV(0); // Interrupt Enable;
	TIM6->CR1 |= _BV(0);
}

/**
  * @brief   Main program.
  * @param  None
  * @retval None
  */
int main(void)
{
  /* System Clocks Configuration */
  RCC_Configuration();   

  /* Once the DAC channel is enabled, the corresponding GPIO pin is automatically 
     connected to the DAC converter. In order to avoid parasitic consumption, 
     the GPIO pin should be configured in analog */
  GPIO_Configuration();

  /* TIM2 Configuration */
  TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
  TIM_TimeBaseStructure.TIM_Period = 0xF;          
  TIM_TimeBaseStructure.TIM_Prescaler = 0xF;       
  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_Triangle;
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_2047;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);

  /* DAC channel2 Configuration */
  DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_1023;
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);

  /* Enable DAC Channel1: Once the DAC channel1 is enabled, PA.04 is 
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_1, ENABLE);

  /* Enable DAC Channel2: Once the DAC channel2 is enabled, PA.05 is 
     automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_2, ENABLE);

  /* Set DAC dual channel DHR12RD register */
  DAC_SetDualChannelData(DAC_Align_12b_R, 0x100, 0x100);

  /* TIM2 enable counter */
  TIM_Cmd(TIM2, ENABLE);

  while (1)
  {
  }
}

void analogout_init(dac_t *obj, PinName pin)
{
    static uint8_t dac_initialized = 0;

    /* init in-memory structure */
    analogout_preinit(obj, pin);

    if (!dac_initialized) {
        /* Initialize the DAC. Will disable both DAC channels, so should only be done once */
        /* Use default settings */
        CMU_ClockEnable(cmuClock_DAC0, true);

        DAC_Init_TypeDef init = DAC_INIT_DEFAULT;

        /* Calculate the DAC clock prescaler value that will result in a DAC clock
         * close to 500kHz. Second parameter is zero. This uses the current HFPERCLK
         * frequency instead of setting a new one. */
        init.prescale = DAC_PrescaleCalc(500000, REFERENCE_FREQUENCY);

        /* Set reference voltage to VDD */
        init.reference = dacRefVDD;

        DAC_Init(obj->dac, &init);
        dac_initialized = 1;
    }
    /* Use default channel settings */
    DAC_InitChannel_TypeDef initChannel = DAC_INITCHANNEL_DEFAULT;
    DAC_InitChannel(obj->dac, &initChannel, obj->channel);


}

void main(void) //using 0
{			   
	EA = 0;
	
	//CFG845=0x1;//enable xram
	
	PLLCON&=PLLCON_VAL;//настройка частоты процессора
//-------printf--------
//    T3CON = T3CON_VAL;
//
//    T3FD = T3FD_VAL;
//    SCON =0x52; //0x53;
//---------------------
	
	Timer1_Initialize(); //таймер генерации частоты

	Frequency_Init();
	DAC_Init();
	WDT_Init(WDT_2000);//включить сторожевой таймер

	EA=1;

	while(1)
	{	
	  Frequency_Measure_Process();
	  WDT_Clear();
	}
}

/** 
 * Configure DAC output
 */
void dacSetup(){
  DAC_InitTypeDef DAC_InitStructure;

  /* Enable GPIOA clock */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
  
  /* Configure PA.04 (DAC_OUT1) in analog mode */
  configureAnalogOutput(GPIOA, GPIO_Pin_4);
  /* Configure PA.05 (DAC_OUT2) in analog mode */
/*   configureAnalogOutput(GPIOA, GPIO_Pin_5); */

  /* Enable DAC clock */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
  
  /* DAC channel Configuration */
  DAC_StructInit(&DAC_InitStructure);
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_None;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
/*   DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_LFSRUnmask_Bits10_0; */

  DAC_Init(DAC_Channel_1, &DAC_InitStructure);
/*   DAC_Init(DAC_Channel_2, &DAC_InitStructure); */
  
  /* Enable DAC Channels */
  DAC_Cmd(DAC_Channel_1, ENABLE);
/*   DAC_Cmd(DAC_Channel_2, ENABLE); */
}

/**	\fn void piezo_init()
 *  \brief Initialize pin as analog output. Initialize DAC. Count sine discrete aproximation.
 * */
void piezo_init()
{
    uint32_t i;

    DAC_InitTypeDef DAC_InitStruct;

    // initialize PA5 jako analogovy vystup
    GPIO_InitTypeDef GPIO_InitStructure;
    GPIO_InitStructure.GPIO_Pin = 1<<5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_40MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // enable clock for DA converter
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

    // initialize DAC2
    DAC_StructInit(&DAC_InitStruct);
    DAC_Init(DAC_Channel_2,&DAC_InitStruct);

    DAC_Cmd(DAC_Channel_2, ENABLE);

    // count sine samples
    for(i=0; i<SINE_SAMPLES_COUNT; i++)
    {
        sine_samples[i] = ((sin(((2*M_PI*(double)i)/SINE_SAMPLES_COUNT) -M_PI/2)+1)*(double)0xFFF)/2;
    }
}

/**
  * @brief  Configures the DAC channel 1 with output buffer enabled.
  * @param  None
  * @retval None
  */
void DAC_Config(void)
{
  DAC_InitTypeDef    DAC_InitStructure;
  GPIO_InitTypeDef   GPIO_InitStructure;

  /* Enable GPIOA clock */
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
  
  /* Configure PA.04 (DAC_OUT1) in analog mode -------------------------*/
  GPIO_InitStructure.GPIO_Mode  = GPIO_Mode_AN;
  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_NOPULL;
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* Enable DAC clock */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
  
  /* DAC channel1 Configuration */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_None;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable;

  /* DAC Channel1 Init */
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);
  
  /* Enable DAC Channel1 */
  DAC_Cmd(DAC_Channel_1, ENABLE);
}