When NanoVNA-Saver reads a segment, it reads frequencies, S11, S21. For those running a newer edy555 firmware (0.2.0+) supporting the "scan" function, the command sequence is as follows:
scan 50000 900000000 101
frequencies
data 0
data 1
(Example there for 50 kHz - 900 MHz)
The timing here is as follows, examples from my own NanoVNA:
0.412s: Sending scan command
0.551s: Asked for frequencies
1.320s: Finished receiving frequencies <-- This is where the application primarily waits for the device
1.422s: Asked for S11
1.510s: Done reading S11
1.613s: Asked for S21
1.708s: Done reading S21
Total time spent 1.296 seconds plus the processing done in NanoVNA-Saver. Looks like the time between the app saving data is 1.303, so the application uses 7 milliseconds for its internal processing between segments.
I have tried moving the frequencies to be read later, but the pattern is clear that the first data requested after the "scan" command is slowed down by about 6-800ms.
After each command, the application waits 50ms before it starts emptying the buffer. I doubt that this moves the timings significantly, as emptying the buffers takes more than 50ms in all cases, and the PC speed is not the limit.
I don't know how this looks for different firmwares - I only have the one NanoVNA, and I'm not going to flash all kinds of different firmware on it, as I need it for app development
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However: For devices that do *not* support the scan command, the application sleeps for a full second after setting the sweep span, to allow the NanoVNA to sweep the frequencies requested. Prior to doing this (when the timing was 300ms), I would sometimes see values from the previous frequency span repeated. It was faster, but less reliable - and I made the decision that reliable is more important than fast. The code is there for anyone who wants to change it for their own priorities
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