I have an 8Mhz ATM32u4 that is able to read external pulse inputs at 125ns ticks using InputCapture3 (PC7) on its 16-bit timer. Is there a magical way (bitbanging?) to get around 10ns tick resolution to read pulses? Edit: like ADC conversions to allow 16-bit systems 24-bit accuracy via creative coding, etc.
If there is no magic, I should use a faster CPU? I am limited in coding pretty much to AVR type CPUs in the Arduino IDE. So wondering what AVR CPU would be fast enough for a 10ns tick that is incorporated already into like a Nano, UNO, etc?
Unless I am able to use Pin Interrupts that are able to read at 10ns intervals, then I could use ARM CPU types with Arduino IDE code which does not require me to dive deep into register level language.
Or, is there a stand-alone analog or digital IC that is able to read at 10ns intervals pulses that an Arduino can process?
Edit: I would need to measure the length of a one-shot pulse only, not a continuous or changing signal. Down to 70us length with an accuracy of at least 18ns tick, but preferably 10ns to account for hardware, etc inaccuracies. This one-shot pulse could repeat not more frequently then 1 second apart, but likely several seconds apart. The signal is two positive square waves forming a pulse measuring not less than 70us from the positive rising edge to rising edge. The system measures the pulse length and sends it the user (serial, BLE, etc).
Edit 2: someone suggested a "one-shot pulse stretcher". Interesting concept... The more I am looking into it, the more I think it's a very viable hardware solution to the AVR's processing speed limitation. One may say that this is hardware "bitbanging" by streching out the short pulse to a proportionally longer one that the MCU capture process can measure reliably/accurately. An example is this old IC from Linear Tech. See Fig 12 and Fig 13. https://www.analog.com/media/en/technical-documentation/data-sheets/6752fc.pdf
The shortest expected pulse would be about 70us which needs to be measured at (around) a resolution of 18ns for the accuracy I need. So I went with 10ns for design to allow for some accuracy "overhead". That is between 4000-7000 counts/ticks (18ns-10ns ticks) for the 70us signal.
If I stretch this same 70us signal to be measured with the pulse-stretcher to 700us and use the currently available 125ns tick interval of the ATM32u4, I should arrive in theory to about the same accuracy as using an 18ns tick for a 70us signal to be measured.
Here is a similar problem that was answered: https://electronics.stackexchange.com/questions/46922/lengthening-a-5-ns-pulse