eTimer MPC5744p

cancel
Showing results for 
Search instead for 
Did you mean: 

eTimer MPC5744p

410 Views
金翅大鹏鸟
Contributor II

Dear ALL,

I used  eTimer0_ch0 of MPC5744P to measure the frequency of a sensor which produces a PWM wave ,frequency(10KHz),Duty(53%). But I get the wrong frequency.Can anyone help me? Thank you ! My code is below:

void eTimer_Init(void)
{
MC_ME.PCTL247.B.RUN_CFG = 0x00; // enable group RUN_PC0 for enable clock
MC_ME.PCTL247.B.LP_CFG = 0x00; // enable group LP_PC0 for enable clock

SIUL2.MSCR[PortA0].B.IBE = 1; // PA0: Enable pad for input - eTimer0 ch0
SIUL2.IMCR[59].B.SSS = 2; // eTimer0 ch0: connected to pad PA0

ETIMER_0.ENBL.R = 0x0; // disable Timer0 channels

ETIMER_0.CH[0].CTRL1.R = 0x3F00; // Counts only rising edge of the MC_CLK (10MHz in RUN0), divide by 128, count up, count repeatedly, rollover
ETIMER_0.CH[0].COMP1.R = 0xFFFF;
ETIMER_0.CH[0].CCCTRL.R = 0x0264; // compare on COMP1 when counting up, COMP2 when counting down
// CAPT2 on falling edge, CAPT1 on rising edge, 2 entries
// free-running mode
ETIMER_0.CH[0].CTRL3.R = 1;

ETIMER_0.ENBL.R = 0x0001; // Enable Timer0 channel 2

ETIMER_0.CH[0].CCCTRL.B.ARM = 1; // starts the input capture process

}

uint16_t capture_ch0[4] = {0};
uint16_t edge1 = 0;
uint16_t edge2 = 0;
uint16_t edge3 = 0;
uint16_t edge4 = 0;
uint16_t counts1 = 0;
uint16_t counts2 = 0;
float pulseH = 0;
float pulseL = 0;
float period = 0;
float freq = 0;
float duty = 0;
void eTimer0_ch0_pro(void)
{
if(ETIMER_0.CH[0].STS.R & 0x0080)
{
capture_ch0[0] = ETIMER_0.CH[0].CAPT1.R;
capture_ch0[1] = ETIMER_0.CH[0].CAPT2.R;
capture_ch0[2] = ETIMER_0.CH[0].CAPT1.R;
capture_ch0[3] = ETIMER_0.CH[0].CAPT2.R;

edge1 = capture_ch0[0];// save 1st rising edge
edge2 = capture_ch0[1];// save 1st falling edge
edge3 = capture_ch0[2]; // save 2nd rising edge
edge4 = capture_ch0[3];// save 2nd falling edge

// calculate period, pulseH, pulseL, freq and duty
if(edge3>edge1)
{
counts1 = edge3 - edge1;
}
else
{
counts1 = (0xFFFF - edge1 +1) + edge3;
}

freq = (float)78125.0/counts1;   //10M/128 = 78125

ETIMER_0.CH[0].STS.R = 0x00C0;
}
}

I run eTimer0_ch0_pro() in the while(1) of main(),

Why do I get the right frequcy?

Labels (1)
0 Kudos
3 Replies

292 Views
PetrS
NXP TechSupport
NXP TechSupport

Hi,

what is the result you got? What is the counts1 value?

You are measuring 10kHz input  using 78.125 KHz reference, this way you lost a resolution a lot.

You should increase reference clock and deal with counter overflows. The overflow can be solved using cascaded channels as it is shown in https://community.nxp.com/docs/DOC-104285 

BR, Petr

0 Kudos

292 Views
金翅大鹏鸟
Contributor II

When MC_CLK  = 10MHz,   I get freq = 831.117004, period = 0.009399999,duty = 15.957448,counts1 = 94, counts2 = 15;

When MC_CLK  = 120MHz,I get freq = 840.053772, period = 0.00930000003,duty = 15.0537624,counts1 = 93, counts2 = 14;

the data I get amost the same.

0 Kudos

292 Views
PetrS
NXP TechSupport
NXP TechSupport

Hi,

if changing MC_CLK you should get different counts1 value. Try to just change the channel prescaler.

Are the capture_ch0 values changing when eTimer0_ch0_pro() is called? Try to disarm capture logic before CAPT are read (ARM=0) and finally start it back.

BR, Petr

0 Kudos