[time-nuts] First success with very simple, very low cost GPSDO, under $8
Tom Van Baak
tvb at LeapSecond.com
Thu Apr 10 19:39:17 UTC 2014
Hi Vlad,
Correct, your code example is the traditional way to keep track of elapsed time without long-term rounding error, although it's usually not attributed to Bézier.
Not sure if you've been following the whole thread, though -- the problem with timer interrupt code is that it can, and will on rare occasion, conflict with 1PPS rising edge pin interrupts. On a microcontroller, for best precision, the solution is to get rid of the timer interrupts, or get rid of the 1PPS interrupts, or both. Secondly, you cannot share multi-byte variables between interrupt level and main level without synchronization or arbitration.
Your code snippet is a good example of what is subtle and dangerous, and dare I say, wrong. You are updating long t_besier in an interrupt handler. Any main level code using t_besier faces byte carry corruption in the multi-byte value of t_besier. True, this works fine on a 32- or 64-bit cpu, but not on an 8- or 16-bit cpu.
/tvb
----- Original Message -----
From: "d0ct0r" <time at patoka.org>
To: <time-nuts at febo.com>
Sent: Thursday, April 10, 2014 10:12 AM
Subject: Re: [time-nuts] First success with very simple, very low cost GPSDO, under $8
>
> I am not sure about Arduino, but probably it too has so-called "timer
> overflow interrupt". If so, then its possible to use that other
> interrupt and some "long" (lets say 32-bit) RAM variable to accumulate
> real value of counter.
>
> In one of my project I was using timer overflow and Besier method to
> make good 1 minutes intervals.
>
> volatile signed long t_besier = 12000000L;
>
> interrupt void TPM2OV_ISR(void)
> {
> TPM2SC = TPM2SC;
> if (TPM2SC_TOF)
> TPM2SC_TOF=0;
> t_besier -= 65536L;
> if(t_besier < 0) {
> t_besier += 12000000L;
> t_time++;
> }
> }
>
More information about the Time-nuts_lists.febo.com
mailing list