Dear lord. The calculator on my iPhone only goes to 1e8 in portrait mode. I had not noticed, so I slipped a decimal place. Doh!!
Sent from my iPhone > On Dec 30, 2020, at 11:48 AM, EJ Kreinar <ejkrei...@gmail.com> wrote: > > > Simple math is not working out for me today-- Maybe it's the holidays?? > > I think a 9000 *byte* packet would be 9000*8/1e9 = 72 microseconds > > ... However the FFT input needs 8192 *samples* which is 8192*4*8/1e9 = 262 > microseconds! > > Seems like your latency is driven by sending data over the network here > > EJ > >> On Wed, Dec 30, 2020, 11:37 AM Marcus D Leech <patchvonbr...@gmail.com> >> wrote: >> Simple math. >> >> A 9000 *byte* packet is 72000 *bits* >> >> At 1.0e9 *bits/sec* that’s a latency of 720usec >> >> >> >> Sent from my iPhone >> >> > On Dec 30, 2020, at 8:55 AM, Jorge Arroyo Giganto via USRP-users >> > <usrp-users@lists.ettus.com> wrote: >> > >> > >> > Hi EJ, >> > >> > Yes, I tried replacing the DMA FIFO with a normal FIFO and the latency got >> > a bit worse and more irregular (I'm guessing that's due to not smoothing >> > that burstiness in the Ethernet interface with the DMA FIFO you mentioned). >> > >> > I have just tried your graph suggestion (Host -> FFT -> FIFO -> Host) and >> > the latency looks about the same but in the FFT block instead. Also I had >> > to use packets with spp=256 in the tx streamer in order to match the spp >> > that the FFT block accepts or I would get an error when building the >> > streamer. Maybe making the FFT block somehow be able to accept bigger >> > packets would decrease the latency? >> > >> > About the theoretical latency for a packet of 8192 bytes you mention, >> > shouldn't it be 8192*4 bytes assuming that each sample is a sc16 (2 bytes >> > for the real part and 2 bytes for the imaginary part of each sample)? Then >> > this latency I am experiencing would make more sense? >> > >> > Thank you so much for your feedback, I will also keep in mind your comment >> > about the way I am using RFNoC. >> > >> > Best regards, >> > >> > Jorge >> > >> > _______________________________________________ >> > USRP-users mailing list >> > USRP-users@lists.ettus.com >> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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