Reads the specified number of samples from the task buffer of an other reader task.

Namespace:  Quanser.Hardware
Assembly:  Quanser.Hardware.Hil (in Quanser.Hardware.Hil.dll)

Syntax

Visual Basic (Declaration)
Function ReadOther ( _
	numSamples As Integer, _
	otherBuffer As Double() _
) As Integer
C#
int ReadOther(
	int numSamples,
	double[] otherBuffer
)
Visual C++
int ReadOther(
	int numSamples, 
	array<double>^ otherBuffer
)
JavaScript
function readOther(numSamples, otherBuffer);

Parameters

numSamples
Type: System..::.Int32
The number of samples to read from the task buffer. Each "sample" consists of all the other input channels specified when the task was created using TaskCreateOtherReader(Int32, array<Int32>[]()[]). For example, if numSamples is 5 and the task is configured to read three channels, then the output buffer will contain 15 elements.
otherBuffer
Type: array< System..::.Double >[]()[]

An array for receiving the values read from the other inputs. The array must contain numChannels * numSamples elements, where numChannels is the number of channels specified when the task was created. The array is organized as a linear array of samples, with each sample consisting of a group of channels. For example, if other input channels 0, 1 and 3 are being read, than the data appears in the array as follows, where the numbers correspond to channel numbers:

0 1 3 0 1 3 ...

Return Value

The return value is the number of samples read from the task buffer. This value may be less than the requested number of samples (including 0) if the task is stopped or has finished processing the total number of samples indicated in the call to Start(Hil..::.Clock, Double, Int32).

Remarks

The ReadOther method reads the specified number of samples from the task buffer of a task created using the TaskCreateOtherReader(Int32, array<Int32>[]()[]) method. If there's not enough samples in the task buffer, then this method will block until the requested number of samples becomes available or the task stops. Since the task reads the hardware at the sampling rate specified in the call to Start(Hil..::.Clock, Double, Int32), and stores the data in the task buffer, this method will never block for longer than the requested number of samples times the sampling period.

Because this method blocks until enough data is available and the task buffer is filled at a given sampling rate, calling this method synchronizes the caller to that sampling rate (provided the task buffer is not being filled faster than we can read the data). Thus, the ReadOther method may be used to implement control systems, system identification, synchronous data streaming and other operations requiring a fixed sampling rate. For control systems, the numSamples parameter is typically 1, since control calculations need to be performed on each sample. For data streaming, the numSamples parameter is typically half the number of samples in the task buffer to implement double-buffering.

Examples

This example illustrates how to read other inputs using a task. The task reads other channels 0-3 every millisecond using a hardware clock. The data may be processed each sampling instant. It runs for 5 seconds before stopping. Exceptions are ignored for simplicity.
C# Copy Code
int [] channels        = { 0, 1, 2, 3 };
double frequency       = 1000;
int    samples         = 5000;
int    samplesInBuffer = frequency;
int    samplesToRead   = 1;

double [] buffer = new double [samplesToRead * channels.Length];
Hil.Task task;

task = card.TaskCreateOtherReader(samplesInBuffer, channels);
task.Start(Hil.Clock.Hardware0, frequency, samples);
for (int index = 0; index < samples; index += samplesToRead) {
    /* Block (if necessary) waiting for next samplesToRead samples */
    task.ReadOther(samplesToRead, buffer);

    /* ... process sample ... */
}
task.Stop();
Visual Basic Copy Code
Dim channels() As Integer = {0, 1, 2, 3}
Dim frequency as Double = 1000
Dim samples As Integer = 5000
Dim samplesInBuffer As Integer = frequency
Dim samplesToRead As Integer = 1

Dim buffer(samplesToRead * channels.Length - 1) As Double
Dim task As Hil.Task
Dim index As Integer

task = card.TaskCreateOtherReader(samplesInBuffer, channels)
task.Start(Hil.Clock.Hardware0, frequency, samples)
For index = 0 To samples - 1 Step samplesToRead
    ' Block (if necessary) waiting for next samplesToRead samples
    task.ReadOther(samplesToRead, buffer)

    ' ... process sample ...
Next
task.Stop()
Visual C++ Copy Code
array<int>^ channels        = { 0, 1, 2, 3 };
double      frequency       = 1000;
int         samples         = 5000;
int         samplesInBuffer = frequency;
int         samplesToRead   = 1;

array<double>^ buffer = gcnew array<double>(samplesToRead * channels->Length);
Hil::Task^ task;

task = card->TaskCreateOtherReader(samplesInBuffer, channels);
task->Start(Hil::Clock::Hardware0, frequency, samples);
for (int index = 0; index < samples; index += samplesToRead) {
    /* Block (if necessary) waiting for next samplesToRead samples */
    task->ReadOther(samplesToRead, buffer);

    /* ... process sample ... */
}
task->Stop();

Exceptions

ExceptionCondition
Quanser.Hardware..::.HilException If the read cannot be performed then an exception is thrown. This situtation typically arises if the card does not support other channels or the task buffer overflowed (ran out of space) after the last call to this method.

See Also