Streaming

Push samples to a dataset while a test runs, one block at a time.

Pushing a block

push takes an N-by-C matrix, one column per channel, and one timestamp column shared by all of them. Fill a preallocated matrix and push it whole.

s     = ds.stream();
chans = [s.channel("rpm"), s.channel("egt"), s.channel("psi")];

t = zeros(1000, 1, 'int64');
v = zeros(1000, 3);
for i = 1:1000
    t(i)    = nominal.now();
    v(i, :) = readSample();
end
s.push(chans, t, v);
delete(s);                                 % flushes and waits until the data lands

push blocks when points arrive faster than the network can send them. If your acquisition loop can’t stall, produce the data on a separate thread.

Timestamps

Use nominal.now() and int64 nanoseconds for streaming timestamps. datetime doesn’t hold nanoseconds, so a round trip through it loses precision. Timestamps are taken as given: int64(0) is the epoch.

Tags

Tag a channel to stamp every point pushed through it from then on:

chans(1).tag("bank", "1");

Points pushed earlier keep the tags they were sent with. Keep the number of distinct tag values low: a value that changes with every point belongs in its own channel.

Closing the stream

Deleting the stream, or clearing the last variable that holds it, sends what is still buffered and waits until it has landed. Call delete(s) when the data must be in Nominal before you move on. The points can take a moment to appear in Nominal after that.

Shutdown

You don’t need to call nominal.shutdown(). clear mex, clear all and quitting MATLAB all run it for you.

Call it to shut the toolbox down at a known point, such as the end of a long script. Every nominal object you hold stops working. New objects work as normal.