I am trying to write a double buffered data acquisition program using MFC and a callback function.

i am trying to do a double buffer data acquisition using MFC application framework in Visual Studio.i want to use a callback function to notify when the buffer is half full.do you have some sample reference program that can help me?

What DAQ board are you using? When you installed NI-DAQ you should have selected to install the support files for VC++. Then there will be several examples on how to do double buffered data acquisition.
If you have already installed NI-DAQ 6.8 or higher and did not select to include the support files, you can run the NI-DAQ setup program and just add them. If you are using an older version, you will have to uninstall and reinstall.
Once you have the support files, follow this path to the examples.
>>Program Files>>National Instruments>>NI-DAQ>>Examaples>>Visual C>>
If you are doing digital acquistion, goto the di folder, if you are doing analog acquisition goto the ai folder.
As for the callback function, you can use the NI-DAQ function Config_DAQ_
Event_Message with DAQEvent Type = 1, where N would equal half your buffer.
Brian

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Can PCI 6031E handle multi-buffered data acquisition

If so can anyone send me some instructions or LabView code. Thank you in advance.

Greetings,
The PCI-6031E can handle single or double buffered acquisitions. The two best sources for examples and instructions are LabVIEW itself and our web site. Go to the "Help -> Find Examples" pull-down menu in LabVIEW to search for shipping examples. Look in the folder "Hardware Input and Output -> DAQ -> Analog Input -> General." Here you will find many analog input examples. Specifically, you should pay attention to the ones with "buffered" in the title.
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[email protected]

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Once again: I wish I could claim credit for these classes, but they were in fact posted a year or so ago by someone lese. If I had the name I would give credit.
I've used these for two heavy-duty applications with never a problem.
<code>
package pipes;
import java.io.IOException;
import java.io.InputStream;
* This class is equivalent to <code>java.io.PipedInputStream</code>. In the
* interface it only adds a constructor which allows for specifying the buffer
* size. Its implementation, however, is much simpler and a lot more efficient
* than its equivalent. It doesn't rely on polling. Instead it uses proper
* synchronization with its counterpart PipedOutputStream.
* Multiple readers can read from this stream concurrently. The block asked for
* by a reader is delivered completely, or until the end of the stream if less
* is available. Other readers can't come in between.
public class PipedInputStream extends InputStream {
byte[] buffer;
boolean closed = false;
int readLaps = 0;
int readPosition = 0;
PipedOutputStream source;
int writeLaps = 0;
int writePosition = 0;
* Creates an unconnected PipedInputStream with a default buffer size.
* @exception IOException
public PipedInputStream() throws IOException {
this(null);
* Creates a PipedInputStream with a default buffer size and connects it to
* source.
* @exception IOException It was already connected.
public PipedInputStream(PipedOutputStream source) throws IOException {
this(source, 0x10000);
* Creates a PipedInputStream with buffer size <code>bufferSize</code> and
* connects it to <code>source</code>.
* @exception IOException It was already connected.
public PipedInputStream(PipedOutputStream source, int bufferSize) throws IOException {
if (source != null) {
connect(source);
buffer = new byte[bufferSize];
* Return the number of bytes of data available from this stream without blocking.
public int available() throws IOException {
// The circular buffer is inspected to see where the reader and the writer
// are located.
return writePosition > readPosition ? // The writer is in the same lap.
writePosition - readPosition : (writePosition < readPosition ? // The writer is in the next lap.
buffer.length - readPosition + 1 + writePosition :
// The writer is at the same position or a complete lap ahead.
(writeLaps > readLaps ? buffer.length : 0)
* Closes the pipe.
* @exception IOException The pipe is not connected.
public void close() throws IOException {
if (source == null) {
throw new IOException("Unconnected pipe");
synchronized (buffer) {
closed = true;
// Release any pending writers.
buffer.notifyAll();
* Connects this input stream to an output stream.
* @exception IOException The pipe is already connected.
public void connect(PipedOutputStream source) throws IOException {
if (this.source != null) {
throw new IOException("Pipe already connected");
this.source = source;
source.sink = this;
* Closes the input stream if it is open.
protected void finalize() throws Throwable {
close();
* Unsupported - does nothing.
public void mark(int readLimit) {
return;
* returns whether or not mark is supported.
public boolean markSupported() {
return false;
* reads a byte of data from the input stream.
* @return the byte read, or -1 if end-of-stream was reached.
public int read() throws IOException {
byte[] b = new byte[0];
int result = read(b);
return result == -1 ? -1 : b[0];
* Reads data from the input stream into a buffer.
* @exception IOException
public int read(byte[] b) throws IOException {
return read(b, 0, b.length);
* Reads data from the input stream into a buffer, starting at the specified offset,
* and for the length requested.
* @exception IOException The pipe is not connected.
public int read(byte[] b, int off, int len) throws IOException {
if (source == null) {
throw new IOException("Unconnected pipe");
synchronized (buffer) {
if (writePosition == readPosition && writeLaps == readLaps) {
if (closed) {
return -1;
// Wait for any writer to put something in the circular buffer.
try {
buffer.wait();
catch (InterruptedException e) {
throw new IOException(e.getMessage());
// Try again.
return read(b, off, len);
// Don't read more than the capacity indicated by len or what's available
// in the circular buffer.
int amount = Math.min(len,
(writePosition > readPosition ? writePosition : buffer.length) - readPosition);
System.arraycopy(buffer, readPosition, b, off, amount);
readPosition += amount;
if (readPosition == buffer.length) {
// A lap was completed, so go back.
readPosition = 0;
++readLaps;
// The buffer is only released when the complete desired block was
// obtained.
if (amount < len) {
int second = read(b, off + amount, len - amount);
return second == -1 ? amount : amount + second;
} else {
buffer.notifyAll();
return amount;
package pipes;
import java.io.IOException;
import java.io.OutputStream;
* This class is equivalent to java.io.PipedOutputStream. In the
* interface it only adds a constructor which allows for specifying the buffer
* size. Its implementation, however, is much simpler and a lot more efficient
* than its equivalent. It doesn't rely on polling. Instead it uses proper
* synchronization with its counterpart PipedInputStream.
* Multiple writers can write in this stream concurrently. The block written
* by a writer is put in completely. Other writers can't come in between.
public class PipedOutputStream extends OutputStream {
PipedInputStream sink;
* Creates an unconnected PipedOutputStream.
* @exception IOException
public PipedOutputStream() throws IOException {
this(null);
* Creates a PipedOutputStream with a default buffer size and connects it to
* <code>sink</code>.
* @exception IOException It was already connected.
public PipedOutputStream(PipedInputStream sink) throws IOException {
this(sink, 0x10000);
* Creates a PipedOutputStream with buffer size <code>bufferSize</code> and
* connects it to <code>sink</code>.
* @exception IOException It was already connected.
public PipedOutputStream(PipedInputStream sink, int bufferSize) throws IOException {
if (sink != null) {
connect(sink);
sink.buffer = new byte[bufferSize];
* Closes the input stream.
* @exception IOException The pipe is not connected.
public void close() throws IOException {
if (sink == null) {
throw new IOException("Unconnected pipe");
synchronized (sink.buffer) {
sink.closed = true;
flush();
* Connects the output stream to an input stream.
* @exception IOException The pipe is already connected.
public void connect(PipedInputStream sink) throws IOException {
if (this.sink != null) {
throw new IOException("Pipe already connected");
this.sink = sink;
sink.source = this;
* Closes the output stream if it is open.
protected void finalize() throws Throwable {
close();
* forces any buffered data to be written.
* @exception IOException
public void flush() throws IOException {
synchronized (sink.buffer) {
// Release all readers.
sink.buffer.notifyAll();
* writes a byte of data to the output stream.
* @exception IOException
public void write(int b) throws IOException {
write(new byte[] {(byte) b});
* Writes a buffer of data to the output stream.
* @exception IOException
public void write(byte[] b) throws IOException {
write(b, 0, b.length);
* writes data to the output stream from a buffer, starting at the named offset,
* and for the named length.
* @exception IOException The pipe is not connected or a reader has closed
* it.
public void write(byte[] b, int off, int len) throws IOException {
if (sink == null) {
throw new IOException("Unconnected pipe");
if (sink.closed) {
throw new IOException("Broken pipe");
synchronized (sink.buffer) {
     if (sink.writePosition == sink.readPosition &&
     sink.writeLaps > sink.readLaps) {
     // The circular buffer is full, so wait for some reader to consume
     // something.
     try {
     sink.buffer.wait();
     catch (InterruptedException e) {
     throw new IOException(e.getMessage());
     // Try again.
     write(b, off, len);
     return;
     // Don't write more than the capacity indicated by len or the space
     // available in the circular buffer.
     int amount = Math.min(len,
     (sink.writePosition < sink.readPosition ?
     sink.readPosition : sink.buffer.length)
- sink.writePosition);
     System.arraycopy(b, off, sink.buffer, sink.writePosition, amount);
     sink.writePosition += amount;
     if (sink.writePosition == sink.buffer.length) {
     sink.writePosition = 0;
     ++sink.writeLaps;
     // The buffer is only released when the complete desired block was
     // written.
     if (amount < len) {
     write(b, off + amount, len - amount);
     } else {
     sink.buffer.notifyAll();
</code>

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How can I do a buffered digital acquisition on a single line?

I am using a NI PCI 6110 DAQ and I need to do a continuous buffered data acquisition (sample rate near or above 5 kS/s). The thing is, the acquisition must be done on a single digital line. Some other lines of the digital port are used for something else (some in write mode, others in read), so they have to remain unaffected by the process.
It would certainly be better if it could acquire data at the same speed as an analog input (which will be executing at the same time). In fact, it would have been much easier to only add a channel to the AI and I would have got exactly the results I want, but all the AI (4) of the board have already been used .
The picture I uploaded shows what I'm tryi
ng to do: I acquire analog data and I want to automatically show the moment a deconnection occured. The purple/pink line, which I added manually, is the one causing me trouble. It shows the voltage (0-5V) of the relay doing the deconnection (that's why it have to be done at the same time than an AI data acquisition).
Thanks for reading this to the end
Attachments:
Graph.jpg ‏55 KB

Well, you can't get hardware-timed DIO with the 6110, but you can probably use its counters to capture the timestamp you need.
One method would be to set up a buffered edge-counting task. The analog input's sample clock would be specified as the source signal. This will cause the counter's value to increment at the beginning of each sampling cycle, acting as a measure of time from the start of analog input.
The falling edge of the relay signal would be the counter's gating signal. For each instance that the relay disconnects, the count value ("time") at that instant will be stored in the counter's buffer for subsequent retrieval.
Note one small timing subtlety: while the very first sample clock edge puts analog data into the 0th array inde
x, it will also be incrementing the counter time to 1. This off-by-one deviation will persist.
There are other variations on this theme, depending on whether you also need to capture re-connection times, or whether there is always one and only one disconnect of interest, etc. You can likely get just the behavior you need using one or both of the on-board counters.
-Kevin P.

I am trying to write a double buffered data acquisition program using MFC and a callback function.

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