PeriodicStreamOut [LJM User's Guide]

Requires LJM 1.2100 or later.

Initializes device registers and sends waveform data to a device stream buffer to output a periodic waveform. Calling this function will enable an out-stream that will loop over data values written to it when LJM_eStreamStart is called, then stop streaming values when LJM_eStreamStop is called.

Syntax

LJM_ERROR_RETURN LJM_PeriodicStreamOut(
int Handle,
int StreamOutIndex,
int TargetAddr,
double ScanRate,
int NumValues,
const double * aWriteData)

Parameters

Handle [in]

A device handle. The handle is a connection ID for an active device. Generate a handle with LJM_Open or LJM_OpenS.

StreamOutIndex [in]

The number assigned to this stream-out. See the Stream Out section of the T-series datasheet for more information.

TargetAddr [in]

The target register to send stream-out data to. See the Stream Out section of the T-series datasheet for a list of potential targets.

ScanRate [in]

The desired number of scans per second. Should be the same value as set in LJM_eStreamStart. Keep in mind that data rate limits are specified in Samples/Second which is equal to NumAddresses * Scans/Second or NumAddresses * ScanRate.

NumValues[in]

The number of values to write to the stream-out buffer. This is also the number of values that will be looped over.

aWriteData[in]

The data array to be written to the stream-out buffer.

Returns

LJM errorcodes or 0 for no error.

Setting Up Periodic Stream-Out

For each waveform being streamed out:

1. Choose which target channel will output the waveform

2. Call LJM_PeriodicStreamOut

3. Start stream with STREAM_OUT#(0:3) in the scan list

4. Stop stream

Target Selection

The periodic stream-out functions use the same targets as listed on the stream-out page.

• DAC0

• DAC1

• FIO_STATE

• FIO_DIRECTION

• EIO_STATE

• EIO_DIRECTION

• CIO_STATE

• CIO_DIRECTION

• MIO_STATE

• MIO_DIRECTION

Call LJM_PeriodicStreamOut

Call LJM_PeriodicStreamOut with the selected target.

Start Stream

Next, start stream with STREAM_OUT#(0:3) in the scan list. The stream-out index must match the index value passed to LJM_PeriodicStreamOut.

The order of STREAM_OUT#(0:3) in the scan list determines when the target is updated. For example, if STREAM_OUT3 is before STREAM_OUT0 in the scan list, STREAM_OUT3_TARGET will be updated before STREAM_OUT0_TARGET.

Stop Stream

To stop stream, use LJM_eStreamStop.

Remarks

LJM_PeriodicStreamOut sets the device stream out buffer (STREAM_OUT#(0:3)_BUFFER_ALLOCATE_NUM_BYTES) to 16384.

Configuration

This function writes to the following registers. When using LJM_PeriodicStreamOut for a given stream index, they should not be set manually:

• STREAM_OUT#(0:3)_TARGET

• STREAM_OUT#(0:3)_BUFFER_ALLOCATE_NUM_BYTES

• STREAM_OUT#(0:3)_LOOP_NUM_VALUES

• STREAM_OUT#(0:3)_ENABLE

• STREAM_OUT#(0:3)_BUFFER_U16

• STREAM_OUT#(0:3)_SET_LOOP

Example

PeriodicStreamOut Example

int handle;
int err = 0;
double scanRate = 1000;
int runTimeMS = 5000;
enum { NUM_SCAN_ADDRESSES = 1 };
const char * scanList[NUM_SCAN_ADDRESSES] = {"STREAM_OUT0"};
int targetAddr = 1000; // DAC0
int streamOutIndex = 0;
int samplesToWrite = 512;

// Make an arbitrary waveform that increases voltage linearly from 0-2.5V
double * values = new double[samplesToWrite];
double increment = double(1) / samplesToWrite;
for (int i = 0; i < samplesToWrite; i++) {
    double sample = 2.5*increment*i;
    values[i] = sample;
}

// Open first available LabJack device
err = LJM_Open(LJM_dtANY, LJM_ctANY, "LJM_idANY", &handle);
ErrorCheck(err, "LJM_Open");
PrintDeviceInfoFromHandle(handle);
ErrorCheck(err, "PrintDeviceInfoFromHandle");

err = LJM_PeriodicStreamOut(
    handle,
    streamOutIndex,
    targetAddr,  
    scanRate,
    samplesToWrite,
    values
);
ErrorCheck(err, "LJM_PeriodicStreamOut");

int scansPerRead = scanRate/ 2;
int aScanList[NUM_SCAN_ADDRESSES];
int aTypes[NUM_SCAN_ADDRESSES];
int deviceScanBacklog;
int ljmScanBacklog;
err = LJM_NamesToAddresses(
    NUM_SCAN_ADDRESSES,
    scanList,
    aScanList,
    aTypes
);
ErrorCheck(err, "LJM_NamesToAddresses scan list");
err = LJM_eStreamStart(
    handle,
    scansPerRead,
    NUM_SCAN_ADDRESSES,
    aScanList,
    &scanRate
);
ErrorCheck(err, "LJM_eStreamStart");

// Run for some time then stop the stream
MillisecondSleep(runTimeMS);
printf("Stopping stream...\n");
err = LJM_eStreamStop(handle);
ErrorCheck(err, "Problem closing stream");
err = LJM_Close(handle);
ErrorCheck(err, "Problem closing device");
delete[] values;