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Analyzing CSS with BERT

How can you go about using BERT with CSS? A test scenario might include a test setup whereby CSS is fed with multiple channels of a PRN23 (or other) pattern and the output of the CSS analyzed for any issues using another BERT instance. Let’s take a look at how these setups might work.

Prerequisites​

We'll be using BERT to analyze a single CSS serial channel. BERT does not use a sync pattern, so you may need to configure your CSS to use Blocked mode.

Configure CSS​

First we need to get CSS set up for its output to be available. Start by checking the box Pull Endpoint, and optionally give it a user-friendly name of your choice.

outputs

Commit the change by clicking Restart and we’ve now made the output accessible to be read.

Configure BERT Analyzer​

After creating or selecting a BERT, enable the Receive channel to read the CSS output.

bert rx

We’ll stick with the default PRN23 pattern, but you should select the pattern type relevant to your case.

Start the BERT instance. Until you start feeding the pattern data to the Sources, you won’t see any values changing.

running bert rx

Latency​

Once the data starts flowing, you’ll start to see CSS report bits flowing. A caveat when starting BERT data on the sources can be that the pattern generators start offset from one another, as might happen in a manually started scenario. You might see something like the following and wonder why only the first Source is meaningfully participating.

uncorrelated

In this case you can see a pretty obvious difference in bit counts, so there’s clearly a fairly large offset in the patterns, even though they may all be perfect. You may need to take steps to ensure the data streams are reasonably aligned as in areal-world scenario. For instance,

  • Ensure the BERT data for each channel starts as close to the same time as possible
  • Lower the bit rate so it's easier to start the data more closely aligned
  • Adjust the CSS configuration to account for the offset in the data (see below for more)

Adjusting the Offest Buffer​

Click Configure… to open the configuration dialog.

You’ll need to adjust the Source Time Offsets and Latency Tolerance value. Adjust this up a ways to try to span the gap between sources.

gap buffer

After adjusting and restarting, assuming the value can buffer and span the offsets, you’ll start to see the CSS working after an initial short period of buffering.

voting

You’ll need to restart the BERT after making changes to the CSS as the BERT will have stopped after the CSS restart. Once started you should start to see results.

good bert rx