GPT tick problem in IMX6SX

piljae — Wed, 21 Feb 2024 07:56:21 GMT

hello
I want to make timer using GPT.
Using pthread, we are going to check the event every 50ms and time measurement.
CPU : IMX6XS

OS : QNX

timer_create example code
------------------------------------------------------------------------------------
/*
* * Demonstrate how to set up a timer that, on expiry,
* * sends us a pulse. This example sets the first
* * expiry to 0.05 seconds and the repetition interval
* * to 0.05 seconds.
*/

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
#include <sys/netmgr.h>
#include <sys/neutrino.h>

#define MY_PULSE_CODE _PULSE_CODE_MINAVAIL

typedef union {
struct _pulse pulse;
/* /* your other message structures would go
here too */
} my_message_t;

int main()
{
struct sigevent event;
struct itimerspec itime;
timer_t timer_id;
int chid;
int rcvid;
my_message_t msg;
struct sched_param scheduling_params;
int prio;

chid = ChannelCreate(0);

/* Get our priority. */
if (SchedGet( 0, 0, &scheduling_params) != -1)
{
prio = scheduling_params.sched_priority;
}
else
{
prio = 10;
}

event.sigev_notify = SIGEV_PULSE;
event.sigev_coid = ConnectAttach(ND_LOCAL_NODE, 0,chid,_NTO_SIDE_CHANNEL, 0);
event.sigev_priority = prio;
event.sigev_code = MY_PULSE_CODE;
timer_create(CLOCK_MONOTONIC, &event, &timer_id);

itime.it_value.tv_sec = 0;
/* 50 million nsecs = .05 secs */
itime.it_value.tv_nsec = 50000000;
itime.it_interval.tv_sec = 0;
/* 50 million nsecs = .05 secs */
itime.it_interval.tv_nsec = 50000000;
timer_settime(timer_id, 0, &itime, NULL);

/*
* * As of the timer_settime(), we will receive our pulse
* * in 0.05 seconds (the itime.it_value) and every 0.05
* * seconds thereafter (the itime.it_interval)
*/
calulateTick(START);
for (;;) {
rcvid = MsgReceive(chid, &msg, sizeof(msg), NULL);
if (rcvid == 0) { /* we got a pulse */
if (msg.pulse.code == MY_PULSE_CODE) {
calulateTick(END);
} /* else other pulses ... */
} /* else other messages ... */
}
return(EXIT_SUCCESS);
}

0x02098024 : GPT_CNT register address
clockValue = 24MHz / 2^3 = 3Mhz

calculateTick(int startEnd)
{
if(START == startEnd){
startTime = ReadReg(0x02098024);
}else if(END == startEnd){
endTime = ReadReg(0x02098024);
diffTimeToMs = (endTime - startTime) / (clockValue);
startTime = endTime;
}
--------------------------------------------------------------
in action
The difference between DiffTimeToMs is not exactly 50ms.
The difference between the values is about 49947 to 49968us.

However, using the function of clock_getime shows a difference of exactly 50 ms.
I would like to know why the difference between reading directly from the register and clock_getime, which is the qnxos function.

topic GPT tick problem in IMX6SX in Embedded Software and Tools Clinic

GPT tick problem in IMX6SX