I found this article:
The equal precision frequency measurement is also known as multi-cycle synchronous frequency measurement method. Its most prominent feature is that the actual gate time is not a fixed value, but a value related with the measured signal, it is exactly an integer multiple of the measured signal period. Within the time allowed counting, we count pulse numbers of the standard signal and the measured signal at the same time, then derive the frequency of the measured signal through mathematical formula.
https://file.scirp.org/pdf/ENG20121000003_88356912.pdf
And this other one:
Time-to-digital converter (TDC) is a device used to measure time interval, which converts the time interval into the digital output. Digital TDCs use internal propagation delays of signals through gates to measure time intervals with very high resolution [19]. A start pulse propagates through the delay line, and its statuses along the delay line will be recorded by flip-flops triggered upon the arrival of a stop pulse. Then, the time interval between the start and stop pulse is obtained by decoding the statuses [20]. In view of this, the proposed method uses FPGA and TDC to accurately measure the time of multiple cycles of the measured signal.
https://www.jstage.jst.go.jp/article/elex/advpub/0/advpub_16.20190310/_pdf/-char/ja
The FPGA seems to be more attractive for this type of service than the microcontroller. I'm going to try this project with Attiny2313, previously mentioned link, then I'll see if I can do it with EPM240, as I already have a board with a dedicated 50MHz oscillator.
Thank you.
