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How do I know if my capture unit is able to stream data?

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How do I know if my capture unit is able to stream data?

‘Streaming data’ is the ability to send data to the Exostiv Probe that exceed the storage reserved in the capture unit FPGA memory.
This mode of transfer is selected in the Exostiv Dashboard Analyzer (or the Exostiv Blade client) – the alternative mode being ‘burst to probe’.
Stream to probe mode selection in the analyzer

In a first approach, the capture unit is able to stream data out if the bandwidth required to sample data (sampling frequency x number of bits) is lower or equal to the bandwidth available at the transceivers (SERDES).

However, there are additional parameters that condition this ability, like the internal granularity of the IP, the bandwidth efficiency of the DDR accesses in the Exostiv Probe (or Exostiv Blade), and so on. The following article provides a formal computation: ‘How many nodes can I sample continuously without creating overflows?’.

Exostiv Dashboard and Exostiv Blade client provide this information in their graphical interface – check the ‘Capture Unit Status’ section’ in the core inserter. This section is available for all capture units (see picture below).

Capture unit status allows checking if streaming mode is possible

For the ‘Capture Unit Status’ to provide a correct information, the following data is required:

  1. The width of the capture unit in bits. In ‘Netlist insertion mode’, this value is automatically computed after the nodes to be observed from the target design are selected. In ‘RTL insertion mode’, this value is an input field that needs to be speficied when setting up core generation.
  2. The frequency of the sampling clock. Worth noting, this value is not automatically detected and must be provided. In Exostiv Dashboard, this value is optional; in Exostiv Blade client, this value must be entered. The value must be entered as MHz.

The ‘Capture Unit Status’ returns the following information:
‘Sampling clock’ subsection.

  1. Whether ‘streaming’ is possible or not at the specified sampling frequency. It also provides the maximum number of bit (max width) of the capture unit to be able to stream at the specified sampling frequency.
  2. For the specified capture unit width, it provides the maximum sampling frequency at which streaming remains possible.

  3. It reminds the user that the ‘burst to probe’ mode remains a valid option, as it uses a flow control mechanism with back pressure to prepare and send bursts of data from a buffer implemented in the target FPGA memory.

‘Data groups efficiency’ subsection
In this section, the tool checks whether all data groups are populated with the specified number of bits. Capture units are generated using the largest of the multipexed data groups connected to it. If a data group is composed of a smaller number of bit, some reserved resources and bandwidth are basically wasted.

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