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5 years, 4 months ago.
Waiting microsecond in RTOS
Hi!
I am developing a device which has to send a package (using CAN-bUS) every 2.5ms, 7.5ms, and 10ms. If I send the pack in advance or late I lose synchrony and my device blocks. I am using 3 threads (could be 2 ;-)) with osPriorityRealtime and a delay inside a forever-one loop. My problem is that I only can reach delays in milliseconds. I mean, I need a delay of 2.5ms but I only can get 2 or 3ms. I had used wait_us, wait, Thread::wait...but it doesn't work
while(1){
wait_us(2500);
//wait(0.0025);
can.send_1();
}
}
could anybody help me?
1 Answer
5 years, 4 months ago.
Hello Bruno,
Below is a test program to measure delays created using wait_us() but without sending any CAN message. The results on LPC1768 seem OK (see below). Maybe it can help:
#include "mbed.h"
Timer timer1, timer2, timer3;
int delay1[20];
int delay2[10];
int delay3[5];
int i1 = 0;
int i2 = 0;
int i3 = 0;
void task1()
{
timer1.start();
while (1) {
timer1.reset();
wait_us(2500);
if (i1 < 20)
delay1[i1++] = timer1.read_us();
else
break;
}
timer1.stop();
}
void task2()
{
timer2.start();
while (1) {
timer2.reset();
wait_us(7500);
if (i2 < 6)
delay2[i2++] = timer2.read_us();
else
break;
}
timer2.stop();
}
int main()
{
Thread* thread1 = new Thread(osPriorityRealtime, OS_STACK_SIZE);
Thread* thread2 = new Thread(osPriorityRealtime, OS_STACK_SIZE);
printf("Starting..\r\n");
thread1->start(task1);
thread2->start(task2);
timer3.start();
while (1) {
timer3.reset();
wait_us(10000);
if (i3 < 5)
delay3[i3++] = timer3.read_us();
else
break;
}
timer3.stop();
printf("-------------\r\n");
for (int i = 0; i < i1; i++)
printf("delay1[%d]=%d\r\n", i, delay1[i]);
printf("-------------\r\n");
for (int i = 0; i < i2; i++)
printf("delay2[%d]=%d\r\n", i, delay2[i]);
printf("-------------\r\n");
for (int i = 0; i < i3; i++)
printf("delay3[%d]=%d\r\n", i, delay3[i]);
}
Results on LPC1768:
Starting.. ------------- delay1[0]=2511 delay1[1]=2511 delay1[2]=2511 delay1[3]=2509 delay1[4]=2512 delay1[5]=2509 delay1[6]=2508 delay1[7]=2509 delay1[8]=2511 delay1[9]=2508 delay1[10]=2511 delay1[11]=2512 delay1[12]=2512 delay1[13]=2508 delay1[14]=2511 delay1[15]=2512 delay1[16]=2511 delay1[17]=2509 delay1[18]=2511 delay1[19]=2508 ------------- delay2[0]=7509 delay2[1]=7510 delay2[2]=7511 delay2[3]=7510 delay2[4]=7511 delay2[5]=7510 ------------- delay3[0]=10012 delay3[1]=10010 delay3[2]=10009 delay3[3]=10010 delay3[4]=10010