How many nodes can I sample continuously without creating overflows?

The number of nodes (or bits) that can be captured continuously with one single capture unit is function of the following parameters:
– The number of transceivers used to extract data : LinkNr – 1 to 4.
– The line rate (or ‘data rate’) : LinkDR – this parameter depends on the transceiver reference clock frequency and is chosen when setting up EXOSTIV IP – up to 12.5 Gbps.
– The frequency of the clock used for sampling the nodes from the FPGA: fSampling
– The fact that we use 98% of the bandwidth of each link for data.
– The grouping of data per link in EXOSTIV IP: G

  • G = 16 bits if transceiver link speed <= 6.6 Gbps
  • G = 32 bits if 6.6 Gbps < tcvr link speed <= 12.5 Gbps
  • G = 64 bits if 12.5 Gbps < tcvr link speed

As a result, the number of bits (NrOfBits) that can be continuously sampled with a capture unit without creating overflows can be computed as follows:

NrOfBits = LinkNr * INT[(LinkDR*0.98) / fSampling / G] * G

– LinkNr = 4;
– LinkDR = 6.6 Gbps (using a reference clock at 132 MHz for the transceivers).
– fSampling = 132 MHz
– G = 16 bits
>>> NrOfBits = 192 bits in this example.

Exostiv Dashboard software and Exostiv Blade client include a tool that automatically verifies if streaming can be used for a specific capture unit. For more details, please check the following article: ‘How do I know if my capture unit is able to stream data?’