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I currently have an nRF transmitter/receiver pair setup on my desk. The transmitter is sending a single byte (0xAA) every 5ms. The receiver sets an LED high to indicate that it received the byte, which is about 10us (+/-2) after the byte was sent. I want to use this nRF pulse for a precise timing/sync application with +/-0.5us accuracy so I need to filter these receiver pulses such that I can estimate the time the transmitter actually sent the byte and the time the next one should arrive. I created an algorithm that uses past nRF pulse times (measured in clock cycles using Teensy's ARM_DWT_CYCCNT register) to estimate the next pulse and it seems to be working reasonably well - though I can't say yet if I'll get the 0.5us accuracy I want.

Now I want to take that estimate and have my microcontroller set an output pin high as soon as the clock count reaches the estimated clock value. Currently I do this by waiting in a while loop and polling the register, but the loop itself takes up several hundred clock cycles which reduces my accuracy. Is there a way to instead have an interrupt trigger when the clock cycle counter reaches my estimated value? I would somehow need to set this interrupt after computing each estimate.

Thanks!

  • Output Compare sounds like your best bet. Set the Output Compare value to your timeout value, and start the timer running from 0 when you get your pulse. When the timer == the OC value the output turns on. – Majenko Mar 8 '17 at 18:27
  • Where's your code? – Enric Blanco Mar 15 '17 at 9:27
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  1. Use a timer to count the system clock and preload the counter with an offset that overflows in the desired cycles.

  2. Use a timer to count the system clock and set a compare match a desired number of cycles out.

To expand the number of cycles, you can do fancier processing in thee Isr but the basic gist IS the same.

Other approaches also exist but the two outlined here are easier.

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