The “HS1” and “HS2” are the clock output and input pins respectively. This isn’t well documented will fix ASAP, as it’s documented on the old CW-Capture page!
So if you feed a 3.3V clock into the HS2 pin (either via the 20-pin header, or the 10-pin single-line header which has HS2 marked on the silkscreen) it should work. You can use the ‘frequency counter’ feature to confirm this.
It actually looks like HS1 is the clock input. Other than that, the frequency counter is showing the correct value now. The current problem I am facing is, that the DCM is losing lock on EXTCLK. I guess this could be because my DUT is running too slowly (~4MHz)? When the ADC source is set to CLKGEN running on 3.3MHz, it seems to work fine though.
EDIT: It also seems that just connecting the clock induces a huge amount of noise into the measurement, is that normal or just my somewhat flaky setup?
Ah damn… not having HW in front of me made it harder to double-check if HS1 or HS2 was correct, apologies!
The DCM has more trouble locking to an external signal if it’s somewhat haphazardly fed in, so it might be a frequency thing. However it could be the signal isn’t very clean due to missing ground or termination issue… can you try adding a series resistor (somewhere in 22 - 100 ohm range) on the clock pin?
The noise might be related to the above, it shouldn’t change things too much. If the clock isn’t reliable it can cause apparent noise due to issues with the ADC/timing margins.
Do you have more details of your setup? Where’s the clock coming from etc.
The extra noise will make things somewhat more difficult (due to worse SNR)… are you routing both a CLK and GND pin? i.e. if you only route the clock as a single wire it will have issues due to lack of return path… even better is a coaxial cable, but just two wires side-by-side (i.e. piece of a ribbon cable, or twisted-pair cable stolen from ethernet cable) will be better!
Connect both the clock and ground on both sides of the system (MCU and CW-Lite board, there is GND pins beside the HS1), I’d still use the series resistor too.