Something to understand about the throttle block is that it doesn’t guarantee a precise sample rate. Just that the long term average rate is what you expect.
Sent from my iPhone > On Feb 26, 2020, at 12:09 PM, Lukas Haase <lukasha...@gmx.at> wrote: > > Hello, > > I use a square wave to generate control/clocking signal for some control > logic: > > https://snipboard.io/WQ8p6d.jpg > > The work function of the "Controller" block looks like: > > def work(self, input_items, output_items): > d = np.diff(input_items[0]) > inds = np.where(d == 1) > for ind in inds[0]: > nedge = self.nitems_read(0) + ind > delta = nedge - self.nedge_prev > print("EDGE @ " + str(nedge) + ", Delta=" + str(delta)) > self.nedge_prev = nedge > return len(output_items[0]) > > I.e., it detects the rising edge. The code above stores the previous edge and > shows the delta between them. > If the frequency of the square wave exactly divides the sampling rate, I > would expect that this delta is always constant/consistent (and I need this > for my application). > > However, with samp_rate=5M and freq=10: > > EDGE @ 10751169, Delta=500054 > EDGE @ 11251224, Delta=500055 > EDGE @ 11751278, Delta=500054 > EDGE @ 12251332, Delta=500054 > EDGE @ 12751387, Delta=500055 > EDGE @ 13251441, Delta=500054 > EDGE @ 13751496, Delta=500055 > EDGE @ 14251550, Delta=500054 > > One interval is not only not always constant but is 54/55 samples larger than > the expected 500000. > When making the interval small (e.g., samp_rate=5M, freq=1k, it works: > > EDGE @ 65072534, Delta=5000 > EDGE @ 65077534, Delta=5000 > EDGE @ 65082534, Delta=5000 > EDGE @ 65087534, Delta=5000 > EDGE @ 65092534, Delta=5000 > EDGE @ 65097534, Delta=5000 > EDGE @ 65102534, Delta=5000 > > I tried tried offsetting the frequency by a slight but but no change. E.g., > freq = 1.0 / (1.0/10 - 1.0/samp_rate) > > I know I could implement a logic that adds a constant directly in the work > function but to keep things manageable I would really prefer to use clock > signals (there will be a bunch of them floating around in the end). > > > Thanks, > Lukas > > > >