Other Parts Discussed in Thread: CC1101, CC1070, CC1310, CC1021
On earlier generations of the CC1xxx radio transceiver parts (i.e. CC1070, CC1101, etc.) we have made use of the ability to output the RF crystal signal (divided down by a pre-scaler) on one of the GPIO pins.
During our manufacturing process we measure this frequency to determine the "zero point" frequency error of the crystal, which we use together with an estimate of the temperature error to calculate the frequency value to program into the part that will produce the desired RF output for a multi-channel FHSS system.
How should I replicate this operation on the CC1310 part? The RF crystal output is not one of the values available (as far as I can tell) for the RFC_GPOx signals.
Since the radio crystal is also shared with the main CPU, I could use the 24 MHz crystal as the system clock and then use a timer module to generate a PWM output on one of the GPIO pins. Is this a reasonable approach?
My goal is to measure the frequency error with a resolution of 0.1 ppm and an accuracy of better than 0.5 ppm. I want to be sure that the PWM output of the timer module does not add any distortion of the crystal timing that would take me past these limits.