To get 8 digits/s your gated counter needs input frequencies >= 100 MHz. Any prescaler will reduce resolution obviously.
That's what I'd like measure anyway (prescaler is just to get the signal in the range that can be directly measured).
A reciprocal counter will give you 8 digits/s @ >= 1 kHz even if you are using your GHz 1000:1 prescaler.
I'm not planning to build a generic purpose frequency meter (thus not so much interest) but let's check a bit via an example to see if I understand correctly.
So let's drive the counter with a 10MHz signal (for simplicity the round value but it could be n*8MHz if this is what GPS receiver good at). Let be the frequency to be measured not 1KHz (which is so easy), but 1234Hz.
So during a single period of the 1234Hz signal there will be 8103.72771475.. periods of the 10 MHz signal.
Obviously the counter won't count fractions, thus sometimes it will be 8103 but probably more frequently 8104.
That corresponds to 1234.11082315...Hz and 1233.95853899... Hz
So a single measurement won't get us to the desired precision. Multiple measurements are needed. The more digits, the more (or longer) measurements.
Here it matters a lot how you do it. You can't simply rely on the ISR getting to the same point of code within the same time after the ISR triggering signal appears on the particular pin (see my previous post) and phase can shift things to wrong direction.
If you do some noise (jitter like or worse some shifting) is added to your measurement that may or may not precisely average out.
The way of exact measurement however is not told/unknown to me.
You don't have anymore total control over the HW or the SW. There are OSs on these things, libraries for SPI, for I2C for OLED/LCD for you name it with its own advantages and disadvantages.
So it's pretty much clear to me that in case of low frequency signals it's not the number of cycles but the period is measured.
But to measure the period a different setup is required, with its own issues.
Now let's get to the practical part: I don't remember the last time when I needed to measure an 1 KHz signal (or 1234Hz signal) with 8 digit precision.
Even more I don't remember the last time when I needed to measure any signal with 8 digit precision below the quite typical 10 MHz.
So I have hobby projects where I do various things in my spare time (mostly tied to RF). No deadline, no boss but still I'd not like to spend all my spare time on it, especially things that I don't see some need for.
synchronising is done by hardware. Interrupts are NO problem!
I guess you are afraid of interrupts.
I'm not afraid of interrupts (I wrote several ISRs, although last time I've not only got my hands dirty with ky-40 rotary encoder to get it 100% right but also burned them as well as I had declare an ISR scoped static variable as volatile although the ISR had IRAM_ATTR...).
If HW can do the synchronization then probably it's good (although so far no-one told the exact solution, which I'm pretty much missing) but still this is not something I'd change platform if it can't be done on what's I'm using, simply I can live without precision measurement of low frequency signals.
Have I missed something?