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Clock Speed

Posted: Wed Jul 13, 2011 12:56 pm
by Mark

The times generated by an interrupt driven clock in Formula Flowcode do not seem to be very accurate. If few questions:

I get the impression that the device is configured to run at 48 MHz, but I see that the Crystal appears to be 4 megahertz, since the configuration parameters are not accessible when using the icon could you let me know what is going on.

My impression is that intensive use of ADC stops the clock working properly. Are the ADC routines interrupt driven?

I am wondering whether I need to be looking into interrupt priorities so as to make sure that the clock operates properly, any comment?

Thanks in advance.

Re: Clock Speed

Posted: Wed Jul 13, 2011 3:01 pm
by Benj

The Formula Flowcode buggy uses a 4MHz ceramic resonator which is then multiplied by the onboard PLL to give a internal clock speed of 48MHz.

The ADC routines are not interrupt driven and should not have any effect on the clock or the timings.

Timer interrupts may not be 100% accurate as we are using a ceramic resonator on this product rather then a crystal. Ceramic resonators should give a fairly accurate clock but can fluctuate slightly with temperature, pressure and humidity.

You may be able to tweak your interrupt timings to give slightly better results for the specific resonator on your buggy or if the board is out of warranty then you could remove the resonator and replace with a 4MHz crystal and 22pf capacitors.