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1. 

   samtal
   Member

   Hi,
   I have a digital input channel that change state every few hundreds millis.
   I need to collect the state change times in an array with 1 mSec resolution.
   I can not use millis() because I need to restart at 0 each time.
   I try to use a Timer, but it gives me a random series of times rather than the real times.
   I am probably doing something wrong.

   Here is a test code:(that does not work as I expect)

   HardwareTimer timer(1);
   uint16 time[20];  //Time stamp array
   uint8 state;
   uint16 counts;
   
   void setup()
   {
     timer.setPeriod(1000);
     Serial1.begin(115200);
   }
   
   void loop()
   {
     int index = 0;
     timer.setCount(0);   //Zero and reset the timer.
     timer.resume();
     do
     {
       state = digitalRead(15);
       while (digitalRead(15)== state) {   } //loop wait for state change
       time[index] = timer.getCount();       //Add time stamp to array.
       index++;
     }
     while (digitalRead(16));
     int i;
     for (i=0;i<10;i++)                //Print the array (testing)
       Serial1.println(time[i]);
   }

   Posted 2 years ago #
2. 

   mlundinse
   Member

   Your timer doesnt count milliseconds, it counts to 1000 and then restarts.
   Use mills() and a variable uint32 time0 to record the starttime of the current state:

   
void loop()
{
int index = 0;
uint32 time0;
do
{
state = digitalRead(15);
time0 = millis();
while (digitalRead(15)== state) { } //loop wait for state change
time[index] = (millis()-time0)&0xFFFF; //Use elapsed number of millis to add time stamp to array.
index++;
}
while (digitalRead(16));
int i;
for (i=0;i<10;i++) //Print the array (testing)
Serial1.println(time[i]);
}


   Posted 2 years ago #
3. 

   samtal
   Member

   Thanks mlundinse.

   Your proposed solution is easy, but, as I wrote, the use of millis() will roll-over at some time (after 49 days from start) and will give erroneous time, while my device is planned to run continuously for years.
   I need a timer with 1 mSec resolution that that will count up to 30 seconds, and will restart for each cycle of my device (this will happen every few hours).
   A solution could be my 1000 mSec timer and a 16 bits counter.
   I therefore try to use one of the ST32 built-in timers.
   I have done this in the past by low level programming (timers registers), and I now try to use the high-level IDE Timer().
   I just don't know how to do it right!

   Posted 2 years ago #
4. 

   mlundinse
   Member

   millis rollover is not a problem, shure the starttime is greater than the endtime when the rollover occurs in the intervall, but the difference will become a small positive number, when converted to unit16 it will still give you the correct number of milliseconds.

   Example:
   start time 10 mills before before rollover t0 = 2^32 - 10
   end time 65 millis after rollover t1 = 65
   elapsed time t1 - t0 = 65 - (2^32 - 10 ) = 65 + 10 - 2^32
   The 2^32 is truncated when using 32 bit registers, so the result will be 65 + 10 = 75 as it should

   Posted 2 years ago #
5. 

   gbulmer
   Moderator

   samtal - arithmetic works correctly even when the unsigned number 'rolls-over'

   Try:
   

   uint32 curTime = 1;
   uint32 prevTime = 0xFFFFFFF0;
   uint32 diff = curTime - prevTime;
   
   Serial1.println(diff);

   The number printed is 17 (1+16)

   Posted 2 years ago #
6. 

   samtal
   Member

   Thanks guys.
   I got it!

   Posted 2 years ago #

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