Waveforms

[artkolisnyk]

Hello. Does anyone know the closest analogy in gRPC to BeginReadWaveform() and EndReadWaveform() from .NET Framework?

[zhindes]

BeginReadWaveform in .NET allows you to setup a callback for an Analog Waveform Read that is invoked when data is available. In the callback, you call EndReadWaveform to get the data before doing it all over again for the next chunk of data. So two things:

1. How do you do a streaming read like that? Look into the moniker streaming example in grpc-device here or the Every N example here
2. How do you get an Analog Waveform? That doesn't exist in the gRPC API. You would need to create your own data type and construct it. Thankfully, its rather simple. Read back the SampClk.Rate attribute using GetTimingAttributeDouble here with TIMING_ATTRIBUTE_SAMP_CLK_RATE here

[bkeryan]

BTW, the asynchronous begin/end read methods in the DAQmx .NET API use the thread pool to call the corresponding synchronous read methods. The Python equivalent is to use concurrent.futures.ThreadPoolExecutor to call a synchronous read method such as task.read() or reader.read_many_sample(). The Python interpreter should drop the GIL (Global Interpreter Lock) while the read method is waiting for data, so that other threads can execute.

[artkolisnyk]

Thanks for the info, guys. I'm gonna try to implement it in .NET 8.

[artkolisnyk]

So, I tried implementing this behavior using the moniker way, but when reading from the response stream I get an error

Status(StatusCode="Unimplemented", Detail="")

Is the moniker functionality implemented on the gRPC server?

Here is a snippet of the relevant C# code for clarity:

await daQmxClient.CreateAIVoltageChanAsync(new()
{
	Task = taskResponse.Task,
	PhysicalChannel = "sim-PCI-6110/ai0",
	NameToAssignToChannel = "test_channel",
	TerminalConfig = InputTermCfgWithDefault.PseudoDiff,
	MinVal = -10.0,
	MaxVal = 10.0,
	Units = VoltageUnits2.Volts,
}, cancellationToken: stoppingToken);

int rate = 10;
int totalSamples = rate * 5;

await daQmxClient.CfgSampClkTimingAsync(new CfgSampClkTimingRequest
{
	Task = taskResponse.Task,
	Rate = rate,
	ActiveEdge = Edge1.Rising,
	SampleMode = AcquisitionType.FiniteSamps,
	SampsPerChan = (ulong)totalSamples
}, cancellationToken: stoppingToken);

BeginReadAnalogF64Response? beginReadResponse = await daQmxClient.BeginReadAnalogF64Async(new()
{
	Task = taskResponse.Task,
	NumSampsPerChan = rate,
	Timeout = 5.0,
	FillMode = GroupBy.GroupByChannel,
	ArraySizeInSamps = (uint)rate
}, cancellationToken: stoppingToken);

using AsyncServerStreamingCall<MonikerReadResponse>? monikerReadResponse =
	monikerClient.StreamRead(new() { ReadMonikers = { beginReadResponse.Moniker } });

while (await monikerReadResponse.ResponseStream.MoveNext(stoppingToken)) // getting an error here
{
	MonikerReadResponse current = monikerReadResponse.ResponseStream.Current;
	
	// some logic
}

[zhindes]

It looks like that moniker based streaming requires enabling a feature toggle. See this wiki: Moniker based streaming for NI Drivers

[artkolisnyk]

Yes, it does indeed. Many thanks.