Hi
I'm having underflow issues while I was trying to transmit signals with higher sampling rate.
Here's my hardware configuration:
I have four 120 MHz USRP-2943 connecting to four PXIe-8374s, these 8374s are inserted on a PXIe-1082 chassis, and the controller is PXIe-8880.
As for the software, I'm using LabVIEW 2015's template Multi-devices Tx Streaming Time (Host).vi.
My goal is to achieve transmission with 8 Tx antennas in total at 61.44 MHz sampling rate for each Tx antenna, and here's the problem I encountered: I'm able to transmit signals with both Tx antennas on one 2943 (2 Tx antennas in total) at 61.44 MHz sampling rate, or one Tx antenna on two 2943s (2 Tx antennas in total) at 61.44 MHz sampling rate, but I can do with both Tx antennas on two 2943s (4 Tx antennas in total) at 61.44 MHz sampling rate.
Other configurations like 4 Tx antennas in total at 30.72 MHz sampling rate or 8 Tx antennas in total at 15.36 MHz sampling rate works, but it seems like the Tx FIFO Underflow message will appear if the product of "number of total Tx antennas" and "sampling rate" goes beyond 122.88.
I've read about that the PXIe-1082 controller provides up to 2 GB/s (single direction) per PXI Express slot dedicated bandwidth (x4 PCIe), and since sending signals with 2 Tx antennas at 61.44 MHz sampling rate means that the data sent in a second is 61.44M (sample) x 2 (IQ) x 2B (2 Byte for each I and Q) x 2 (antenna) = 491.52 MB/sec, I think the PXIe-1082 is capable of handling these data, but I'm not sure if the PXIe-8880 is capable as well.
So my question is:
1. Does anyone know the limit of PXIe-8880 ? Can it handle signals for 8 Tx antennas at 61.44 MHz (roughly 2 GB/s) ?
2. Any thought on the bottleneck of this issue ? Maybe the hardware is all good, and the bottleneck actually exists in the software (LabVIEW project) ?
3. Can the loop that write Tx data in the Multi-devices Tx Streaming Time (Host).vi template be the bottleneck ?
Thanks in advance.
Ikigai
