【经验】用STK3700评估板采集EFM32GG低功耗32位MCU外部频率信号完整周期的经验

最近在调试EFM32GG系列的MCU，想测试外部频率信号的周期。翻看了Simplicity Studio下面的范例程序和应用笔记，只有应用笔记AN0014的范例程序timer_input_capture_dma.slsproj接近需求。但范例程序测试的是按键按下的时间，也就是对应的是半个周期，不是完整的周期信号。针对范例程序我做了如下修改（修改部分用红色字体标识），实现了对外部频率信号周期时间的计算。

频率捕捉不用中断方式用的DMA多次连续采集，采集的数据放到了DMA的BUFFER里面，用BUFFER后面的数减去前面的数据然后再求平均值，这样省了中断的频繁进入也实现了连续累加计数，提高了精度。

捕捉时钟设置的是3.5M，现在采集的数据差是35，采集结果如下表截图，对应采集的100KHz。

下面是对应的代码：

#define DMA_CHANNEL_TIMER0       0

#define BUFFERSIZE               30

volatile uint16_t bufferA[BUFFERSIZE];

volatile uint16_t bufferB[BUFFERSIZE];

/* DMA callback structure */

DMA_CB_TypeDef cb;

/* TOP reset value is 0xFFFF so it doesn't need

   to be written for this example */

#define TOP 0xFFFF

/* 13761 Hz -> 14Mhz (clock frequency) / 1024 (prescaler) */

#define TIMER_FREQ 3500000//13671

#if defined ( STK3700 )

  #define PB0_PORT gpioPortB

  #define PB0_PIN 11//9

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN11//9

#elif defined ( STK3300 )

  #define PB0_PORT gpioPortD

  #define PB0_PIN 8

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN8

#elif defined ( STKG8XX )

  #define PB0_PORT gpioPortB

  #define PB0_PIN 9

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN9

#elif defined ( STK3600 )

  #define PB0_PORT gpioPortB

  #define PB0_PIN 9

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN9

#elif defined ( STK3200 )

  #define PB0_PORT gpioPortC

  #define PB0_PIN 8

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN8

#elif defined ( STK3400 )

  #define PB0_PORT gpioPortC

  #define PB0_PIN 9

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN9

#elif defined ( STK3401 )

  #define PB0_PORT gpioPortF

  #define PB0_PIN 6

  #define PB0_PRS_SIGSEL_PIN PRS_CH_CTRL_SIGSEL_GPIOPIN6

#else

  #error "undefined KIT"

#endif

/**************************************************************************//**

 * @brief  Call-back called when transfer is complete

 *****************************************************************************/

void transferComplete(unsigned int channel, bool primary, void *user)

{

  (void) user;

  /* Re-activate the DMA */

  DMA_RefreshPingPong(channel,

                      primary,

                      false,

                      NULL,

                      NULL,

                      BUFFERSIZE - 1,

                      false);

}

/**************************************************************************//**

 * @brief Configure DMA for Ping-Pong transfers

 *****************************************************************************/

void setupDma(void)

{

  DMA_Init_TypeDef        dmaInit;

  DMA_CfgChannel_TypeDef  chnlCfg;

  DMA_CfgDescr_TypeDef    descrCfg;

  /* Initializing the DMA */

  dmaInit.hprot        = 0;

  dmaInit.controlBlock = dmaControlBlock;

  DMA_Init(&dmaInit);

  /* Setup call-back function */ 

  cb.cbFunc  = transferComplete;

  cb.userPtr = NULL;

  /* Setting up channel */

  chnlCfg.highPri   = false;

  chnlCfg.enableInt = true;

  chnlCfg.select    = DMAREQ_TIMER0_CC0;

  chnlCfg.cb        = &cb;

  DMA_CfgChannel(DMA_CHANNEL_TIMER0, &chnlCfg);

  /* Setting up channel descriptor */

  descrCfg.dstInc  = dmaDataInc2;

  descrCfg.srcInc  = dmaDataIncNone;

  descrCfg.size    = dmaDataSize2;

  descrCfg.arbRate = dmaArbitrate1;

  descrCfg.hprot   = 0;

  DMA_CfgDescr(DMA_CHANNEL_TIMER0, true, &descrCfg);

  DMA_CfgDescr(DMA_CHANNEL_TIMER0, false, &descrCfg);

  /* Enabling PingPong Transfer*/ 

  DMA_ActivatePingPong(DMA_CHANNEL_TIMER0,

                       false,

                       (void *)&bufferA,

                       (void *)&(TIMER0->CC[0].CCV),

                       BUFFERSIZE - 1,

                       (void *)&bufferB,

                       (void *)&(TIMER0->CC[0].CCV),

                        BUFFERSIZE - 1);

}

/**************************************************************************//**

 * @brief  Main function

 * Main is called from __iar_program_start, see assembly startup file

 *****************************************************************************/

int main(void)

{ 

  /* Initialize chip */

  CHIP_Init();

  /* Enable clock for GPIO module */

  CMU_ClockEnable(cmuClock_GPIO, true);

  /* Enable clock for TIMER0 module */

  CMU_ClockEnable(cmuClock_TIMER0, true);

  /* Enable clock for PRS module */

  CMU_ClockEnable(cmuClock_PRS, true);

  /* Setup DMA */

  setupDma();

  /* Configure PB0_PIN as an input for PB0 button with filter and pull-up (dout = 1)*/

  GPIO_PinModeSet(PB0_PORT, PB0_PIN, gpioModeInputPullFilter, 1);

  /* Select PB0_PIN as external interrupt source*/

  GPIO_IntConfig(PB0_PORT, PB0_PIN, false, false, false);

  /* Enable PRS sense on GPIO and disable interrupt sense */

  GPIO_InputSenseSet(GPIO_INSENSE_PRS, _GPIO_INSENSE_RESETVALUE);

  /* Select GPIO as source and PB0_PRS_SIGSEL_PIN as signal for PRS channel 0 */

  PRS_SourceSignalSet(0, PRS_CH_CTRL_SOURCESEL_GPIOH, PB0_PRS_SIGSEL_PIN, prsEdgeOff);

  /* Select CC channel parameters */

  TIMER_InitCC_TypeDef timerCCInit =

  {

    .eventCtrl  = timerEventEveryEdge,

    .edge       = timerEdgeFalling,//timerEdgeRising,

    .prsSel     = timerPRSSELCh0,

    .cufoa      = timerOutputActionNone,

    .cofoa      = timerOutputActionNone,

    .cmoa       = timerOutputActionNone,

    .mode       = timerCCModeCapture,

    .filter     = true,

    .prsInput   = true,

    .coist      = false,

    .outInvert  = false,

  };

  /* Configure CC channel 0 */

  TIMER_InitCC(TIMER0, 0, &timerCCInit);

  /* Select timer parameters */ 

  TIMER_Init_TypeDef timerInit =

  {

    .enable     = false,

    .debugRun   = true,

    .prescale   = timerPrescale4,//timerPrescale1024,

    .clkSel     = timerClkSelHFPerClk,

.fallAction = timerInputActionStart,

.riseAction =timerInputActionNone, //timerInputActionStop,

    .mode       = timerModeUp,

    .dmaClrAct  = false,

    .quadModeX4 = false,

    .oneShot    = false,

    .sync       = false,

  };

  /* Configure timer */

  TIMER_Init(TIMER0, &timerInit);

  while(1)

  {

    /* Go to EM1 */

EMU_EnterEM1();

  }

}