Simple low pass digital filter implementation for non-uniform sampling?
You say you have no control over the input sampling rate. That is understood but you are not considering the fact that you can resample once inside your digital system AND, I'm presuming you do have control over that else why would you be asking this question. So, resample your digital data like this: -

Now &quot;real sample&quot; 1 took 25 ms and &quot;real sample&quot; 2 took 29 ms but who cares if you internally resample that data? Yes, you have to process at a much higher rate but it's not like you are having to do major recalculations each time because \$A*X_n\$ is static for 25 to 29 samples.