RTOS causes pausing of RTCC

[dave10]

PIC:- 18F87K22
CCS :- 4.137

Hi Guys

I was hoping to use the RTOS to run several simple tasks which are triggered at times taken from comparing time from RTCC.
With set values in program. The rate these tasks are running is around 1 second.

But when I add this line of code to use the RTOS, RTCC clock start stuttering ?

[temtronic]

I don't use the RTOS but the RTCC module might be the problem.

What are the specs for it? How good it the xtal you're using? If using say an internal RC network, odds are it's not going to be very accurate over time( no pun intended).
I know that trying to use an internal clock source(RC) is not great for high speed serial communications and i suspect the same may be true for the RTCC.

I use a DS1307 for RTC use,maybe 'old fashsion' but I prefer a discrete external device.

I'm sure others will reply..

hth
jay

[Ttelmah]

Also, key thing to remember is that anything reading values updated somewhere 'else', should really take a copy of the values, and display them from this. Remember that a simple print, of a number, takes a relatively long time (divisions, repeated for each digit). What happens if the code reads the minutes as (say) 59, and then by the time it gets to the seconds, the time has updated to 00:00. The display will suddenly jump 'backwards', showing 59:00....
The sequence should always be:
Either disable interrupts for a moment, copy the remote variable to a local copy, and then enable interrupts and display from the copy, or
copy remote variable to local. Verify copy==remote. If not, loop back and copy again. Only once they match (so no update during the copy), then display from the copy.

Best Wishes

[dave10]

Hi

Thank you for the reply. I'm using a external 16Mhz xtal as the main system clock and a tuning fork, 'fox' crystal for the RTCC.
Have I set the fuses correctly. I find it difficult to understand the correct fuses for the device from device file and manual.

I should have set system crystal to external 16 Mhz's and using internal multiplier to 64Mhz with,

[temtronic]

My vote is for the DS1307. It's a tried and true device,zillions in operation worldwide.I think the RTCC is a peripheral that mchp came up with to try to compete with external RTC chips.Have a good look at the timing specs and what's required to keep it ticking(battery backup).I don't know if there's a separate pin for RTCC power.If not, you need a BIG battery to power the PIC and whole PCB just to keep time alive.The benefits of the DS1307 ... easy to use,easy battery backup,accurate timekeeping,SRAM for storage,interrupt to PIC.Sure it makes the PCB bigger but overall the cost is less.
Also consider your R&D time spent on the RTCC vs. the 1307.Since you've already made space for the DS1307, use it.Nothing is worse than finding out 3 months from now that 'I should have don't it' happens!

hth
jay

+++++++++++++++++
temtronic
Topic is internal RTC & how to use.
Do not hijack thread for Maxim sales pitch.
- Forum Moderator
+++++++++++++++++

[andrewg]

[temtronic]

Sorry...
Having see a few threads about problems with the RTCC and since the OP had alrady designed his PCB to accept the other device,my advice was to go with what works and not waste valuable time on what doesn't.
Since no one has posted a driver for the RTCC, I've concluded it's more trouble than it's worth.

jay

[andrewg]

There's no need for anyone to post a driver for the RTCC, it's built into CCS. See setup_rtc() and the various rtc_XXX() functions.
_________________
Andrew

[temtronic]

hmm...according to the help info....

Configures the Real Time Clock and Calendar module. The module requires an external 32.768 kHz Clock Crystal for operation

...so you MUST have an external 'clock crystal', can't run off the internal 31KHz clock.

[dave10]

Hi Guys

Thankyou for your help. RTCC been running for a week and is still pretty accurate. I'll have a play with the external RTC when everything else is finished !

Thanks Dave