CTC Timer Interrupt time millis(), File.write hang on

[minie001]

I have two Compare Interrupts on my Yun.
Everything works fine.
But when i look at the balance that when the interrupts run the code i feel confused.
Maybe somebody can help me.
Timer 3, 16 Bit, Prescaler 64 Interrupt run every 257ms, OCR3A = 64249
When i compare the mills()  the timer is running, most ist 257ms.
but sometimes after 10, 20, 5, 12 ... .. .. cycles sometimes the timer run after 256ms or also 258ms.
is the a feature or something else for making the timer exactly similar like embedded systems?

i write these Data into DB.
I write 4100 Lines in Database and 252 Times the Time is wrong.
Diff -1: 128 Times
Diff +1:122 Times
Diff +2: 2 Times
Timer init is:

 TCCR3A = 0;
 TCCR3B = (1 << WGM32) | (1 << CS31) | (1 << CS30);
 TCCR3C = 0;
 TCNT3 = 0;
 OCR3A = 64249;
 TIMSK3 = (1 << OCIE3A);
Who know how i can resolve this Problem?

[AnalysIR]

The millis() timer on the Arduino isn't 100% accurate. it fluctuates +/- 1 ms (?) at any time, but maintains accuracy over time.
So any millis time measurment could be up to 1 mSec out and rarely spot on to the microsecond.

If you can do your comparisons using elapsed microseconds(), which is 100% accurate all of the time. (subject to the crustal or resonator accuracy)

The millis() accuracy is related to the way it is implemented. A search will provide the details.


This probably expalins what you observed!

[minie001]

Hello, thank you for reply.

I use now micros()/1000 and it works fine, But I have a second Problem.
I use the Bridge to write from the loop every 10 times the interrupt run i set a flag and write into a file from loop (File_Append)
Timer 1 do this every 37ms and Timer 3 every 257ms
It works fine on Linino side I have a cronjob that catch the file every minute and load the data into MySql.
But after a few minutes the Atmega32u4 get busy for 2,3,4...8 minutes and then continue working, also continue work when i reset the atmega32u4. It is like the Bridge hanging on or get busy.
It is necessary if i use File.write or Process.runShellCommand to comunicate with the Linino after many loops the Action corrupt.
I write before open file and after closing file Serial.print(millis()) and it hang before the file is closing.
something wrong or maybe is there a better,faster way to write into linino?

[AnalysIR]

great...

.....unfortunately, I cant be of further help with your other problem(s), but if you figure out a solution do post it.