delay_until

[sinurb]

Hi,

What does the delay_until do? And why did you use "5" as argument?

Thanks

[trainman419]

unsigned long t = 0;

void delay_until(unsigned long ms) {
  unsigned long end = t + (1000 * ms);
  unsigned long d = end - micros();

  // crazy long delay; probably negative wrap-around
  // just return
  if ( d > 1000000 ) {
    t = micros();
    return;
  }
  
  if (d > 15000) {
    unsigned long d2 = (d-15000)/1000;
    delay(d2);
    d = end - micros();
  }
  delayMicroseconds(d);
  t = end;
}

delay_until() and the associated global t is used to wait the specified amount of time since the previous call to delay_until(). This allows me to run the same sequence of code on a schedule, even if individual function calls take a slightly different amount of time each time.

The argument to delay_until is the number of milliseconds to delay (since the previous call to delay_until)

For example, if I have a function foo() that takes 1-2 milliseconds to execute, if I my loop is:

void loop() {
    foo(); // 1-2 mS
    delay(5); // 5 mS
}

The total loop time will be between 6 and 7 milliseconds, instead of the desired 5 milliseconds. Since I cannot predict exactly how long foo() will take, I cannot just adjust the delay.

With delay_until(), this loop always takes 5 milliseconds:

void loop() {
    foo(); // 1-2 mS
    delay_until(5); // wait until 5mS have passed
}

This is particularly important for LIN because the protocol requires that the first set of messages be sent every 5 milliseconds (5mS * 10 messages = 50 mS), and the entire set of messages repeats every 200mS, so at the end of the loop I delay for the remaining 150mS: https://github.com/trainman419/bekant/blob/f3733f8a28a3442db584cdb14d0de5f904b2de64/bekant.ino#L264-L265

Again, the important thing to note here is that if I used a normal delay() between messages or at the end of the main loop, the amount of time that it takes to handle WiFi clients would increase the loop time, and the other LIN devices would probably time out.

[sinurb]

Thanks. OK I understand. But you talk about the protocol asking for 5 ms. Where in LIN specification you found it? Or it is only for this particular case?

On Jan 23, 2018 8:57 PM, "Austin" [email protected] wrote:

unsigned long t = 0;

void delay_until(unsigned long ms) { unsigned long end = t + (1000 * ms); unsigned long d = end - micros();

// crazy long delay; probably negative wrap-around // just return if ( d > 1000000 ) { t = micros(); return; }

if (d > 15000) { unsigned long d2 = (d-15000)/1000; delay(d2); d = end - micros(); } delayMicroseconds(d); t = end; }

delay_until() and the associated global t is used to wait the specified amount of time since the previous call to delay_until(). This allows me to run the same sequence of code on a schedule, even if individual function calls take a slightly different amount of time each time.

The argument to delay_until is the number of milliseconds to delay (since the previous call to delay_until)

For example, if I have a function foo() that takes 1-2 milliseconds to execute, if I my loop is:

void loop() { foo(); // 1-2 mS delay(5); // 5 mS }

The total loop time will be between 6 and 7 milliseconds, instead of the desired 5 milliseconds. Since I cannot predict exactly how long foo() will take, I cannot just adjust the delay.

With delay_until(), this loop always takes 5 milliseconds:

void loop() { foo(); // 1-2 mS delay_until(5); // wait until 5mS have passed }

This is particularly important for LIN because the protocol requires that the first set of messages be sent every 5 milliseconds (5mS * 10 messages = 50 mS), and the entire set of messages repeats every 200mS, so at the end of the loop I delay for the remaining 150mS: https://github.com/ trainman419/bekant/blob/f3733f8a28a3442db584cdb14d0de5 f904b2de64/bekant.ino#L264-L265

Again, the important thing to note here is that if I used a normal delay() between messages or at the end of the main loop, the amount of time that it takes to handle WiFi clients would increase the loop time, and the other LIN devices would probably time out.

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[trainman419]

The 5mS and 200mS loop rates are for this specific application. I measured these timings with my oscilloscope when I was reverse-engineering the protocol for the desk.