K70 - MQX 4.1: Measure an input frequency

[arnogir]

Hello

I'm working on a Kinetis k70 with MQX 4.1.1

I'm looking for a way to measure a Frequency of a square wave  signal on an Input (General IO or a specific IO if needed)

I see we can do something with LPTMR module, but I don't find the way to use it via MQX or with my own code but without interfering with MQX.

Have you some Idea, or exemple allowing to measure a Frequency on an input?

Thank:smileyhappy:

[danielchen · Accepted solution]

Hi Arno:

I think you can try FTM module,   the dual edge capture mode, please read the following document, section 44.4.24

http://cache.freescale.com/files/microcontrollers/doc/ref_manual/K70P256M150SF3RM.pdf?fasp=1

Have a nice day,
Daniel

[arnogir]

Hello

Then I use FTM2 CH0/CH1

I implement the following code, I'm still to test It. I hope I don't forget anything..

But I have a question, Like CH0 and CH1 are combine, Is these Pin are linked internaly or I have to apply my swquare wave signel on both Pin PTF20 and PTF21 (FTM2_CH0 / FTM2_CH1) ?

 /* Activate FTM2 Clock */
 SIM_SCGC3 |= SIM_SCGC3_FTM2_MASK;  
 
 /* Set up mode register */   
 FTM2_MODE = FTM_MODE_WPDIS_MASK | FTM_MODE_FTMEN_MASK;  
 
 /* Clear status and control register */
 FTM2_SC = (uint32_t)0x01UL;  
 
 /* Clear counter initial register */
 FTM2_CNTIN = (uint32_t)0x00UL;  
 
 /* Reset counter register */
 FTM2_CNT = (uint32_t)0x00UL;  
 
 /* Clear channel status and control register */
 FTM2_C0SC = (uint32_t)0x00UL; 
 FTM2_C1SC = (uint32_t)0x00UL;  
 
 /* FTM1_C1SC: CHF=0,CHIE=0,MSB=1,MSA=0,ELSB=1,ELSA=1,DMA=0 */
 /* Set up channel status and control register */
 /* MSnA = 1: Continus Mode */
 /* ElsnB:ElsnA = 0:1 : Rising Edge */
 FTM2_C0SC = FTM_CnSC_MSA_MASK | FTM_CnSC_ELSA_MASK;
 FTM2_C1SC = FTM_CnSC_MSA_MASK | FTM_CnSC_ELSA_MASK;  
 
 
 /* PTF20 and PTF21 -> FTM_CH0, FTM_CH1 */
 PORTF_PCR20 = PORT_PCR_MUX(3);
 PORTF_PCR21 = PORT_PCR_MUX(3);
 
 /* Combine CH0 and CH1 */
 FTM2_COMBINE = FTM_COMBINE_COMBINE0_MASK | FTM_COMBINE_DECAPEN0_MASK; 
 /* Do separatly, because DACAP bit can be set only when DECAPEN = 1 */
 FTM2_COMBINE |= FTM_COMBINE_DECAP0_MASK;
 
 /* Set up status and control register */
 /* ClkSource = Bus Clock, PREDIV = 32 */
 FTM2_SC = (uint32_t)0x0DUL;  
 

Then I get the frequency like that:

  Cpt0 = FTM2_C0V;
 Cpt1 = FTM2_C1V;
 
 /* Calcul Delta counter value*/
 if (Cpt1 >= Cpt0)
 {
 CptCalcul = (uint32_t)(Cpt1 - Cpt0);
 }
 else
 {
 CptCalcul = (uint32_t)(65536 - Cpt0 - Cpt1); 
 }
 
 CptCalcul =  (CptCalcul * DV_FMETER_PRDIV);
 CptCalcul = DV_FMETER_CpuClockSource / CptCalcul;
 

[danielchen]

Hi,

Please see the below picture, if input is CH0, then n=0 , you can get C(0)V[15:0] and C(1)V[15:0].  you have to apply your square wave signal on pin FTM_CH0. 

[arnogir]

Then I done the following correction:

-Don't use external PIN PTF20

-Initialisze MOD register to 0xFFFF, else counter stay at 0.

Initialisation part:

  /* Find out input frequency*/
 DV_FMETER_CpuClockSource = _cm_get_clock(_cm_get_clock_configuration(), CM_CLOCK_SOURCE_BUS);
 
 /* Activate FTM2 Clock */
 SIM_SCGC3 |= SIM_SCGC3_FTM2_MASK;  
 
 /* Set up mode register */   
 FTM2_MODE = FTM_MODE_WPDIS_MASK | FTM_MODE_FTMEN_MASK;  
 
 /* Clear status and control register */
 FTM2_SC = (uint32_t)0x01UL;  
 
 /* Clear counter initial register */
 FTM2_CNTIN = (uint32_t)0x00UL;  
 
 /* Reset counter register */
 FTM2_CNT = (uint32_t)0x00UL;  
 
 /* Clear channel status and control register */
 FTM2_C0SC = (uint32_t)0x00UL; 
 FTM2_C1SC = (uint32_t)0x00UL;  
 
 /* No need modulo, let counter count in all stage */
 FTM2_MOD = 0xFFFF;  
 
 /* FTM1_C1SC: CHF=0,CHIE=0,MSB=1,MSA=0,ELSB=1,ELSA=1,DMA=0 */
 /* Set up channel status and control register */
 /* MSnA = 1: Continus Mode */
 /* ElsnB:ElsnA = 0:1 : Rising Edge */
 FTM2_C0SC = FTM_CnSC_MSA_MASK | FTM_CnSC_ELSA_MASK;
 FTM2_C1SC = FTM_CnSC_MSA_MASK | FTM_CnSC_ELSA_MASK;  
 
 
 /* PTF20 and PTF21 -> FTM_CH0, FTM_CH1 */
 PORTF_PCR20 = PORT_PCR_MUX(3);
 
 /* Combine CH0 and CH1 */
 FTM2_COMBINE = FTM_COMBINE_COMBINE0_MASK | FTM_COMBINE_DECAPEN0_MASK; 
 /* Do separatly, because DACAP bit can be set only when DECAPEN = 1 */
 FTM2_COMBINE |= FTM_COMBINE_DECAP0_MASK;
 
 /* Set up status and control register */
 /* ClkSource = Bus Clock, PREDIV = 32 */
 FTM2_SC = (uint32_t)0x0DUL;  

Get result part:

uint32_t CptCalcul = 0;;
 uint16_t Cpt0;
 uint16_t Cpt1;  
 if (DV_FMETER_Intialised == TRUE)
 {
 /* Get twice counter value */
 Cpt0 = FTM2_C0V;
 Cpt1 = FTM2_C1V;
 
 /* Calcul Delta counter value*/
 if (Cpt1 >= Cpt0)
 {
 CptCalcul = (uint32_t)(Cpt1 - Cpt0);
 }
 else
 {
 CptCalcul = (uint32_t)(65536 - Cpt0 + Cpt1);
 }
 CptCalcul =  (CptCalcul * DV_FMETER_PRDIV);
 CptCalcul = DV_FMETER_CpuClockSource / CptCalcul;
 }