When writing signal data to a TDMS file I always end up with a different number of (Y) double values compared to the number of (X) DateTime timestamps.
What is strange is that DataCount for the channel yields a correct result. However, when opening the file for reading there is always a mismatch between the number of X and Y values, per channel.
I have previously reported a bug concerning the AutoSave property and corrupt data when using TdmsWaveformLayout.PairedTimeAndSampleChannels and WaveformTiming.CreateWithIrregularInterval(). The workaround was to explicitly call Save() whenever modifying the TDMS file, e.g. creating groups/channels or writing sample data. This seemed to work well enough, and I haven't seen corrupt data since. However, I am now experiencing a data loss instead.
Just to be sure I am logging the value reported by DataCount before and after each write operation. In this example 80 samples are written each time. It looks OK:
2010-08-09 11:07:02.254 [9] DEBUG SE.Epiq.Acqis.Storage.TdmsStorage - P0 [mmHg] # before (double/DateTime): 23920/23920
2010-08-09 11:07:02.262 [9] DEBUG SE.Epiq.Acqis.Storage.TdmsStorage - P0 [mmHg] # after (double/DateTime) : 24000/24000
2010-08-09 11:07:02.269 [9] DEBUG SE.Epiq.Acqis.Storage.TdmsStorage - P5 [mmHg] # before (double/DateTime): 4400/4400
2010-08-09 11:07:02.269 [9] DEBUG SE.Epiq.Acqis.Storage.TdmsStorage - P5 [mmHg] # after (double/DateTime) : 4480/4480
But when I open the file and try to read the data I get an error saying "the number of time stamps on the timing channel associated with ... is not equal to the number of data samples.". DataCount confirms this and there is always a multiple of the number of samples written simultaneously that is missing, e.g. 80/160/240/... samples.
If I use the TDMS Reader demo application and click on a timing channel I sometimes (!) get a different error: "Specified argument was out of range of valid values. Parameter name: wholeSeconds.". I don't know if this error is related. The time stamps I am writing are what DateTime.UtcNow returns. Nothing strange at all.
I create/open the TDMS file like this:
... = new TdmsFile(filename, new TdmsFileOptions(TdmsFileFormat.Version20, TdmsFileAccess.ReadWrite, true, TdmsByteOrder.Native));
When I am done writing data, I call Save(), Close(), Dispose() (in that order).
Sample data are written to the file using AppenAnalogWaveform().
channel.Parent.AppendAnalogWaveform(channel, TdmsUtilities.CreateAnalogWaveform(e.Data, e.Signal));
The CreateAnalogWaveform method returns an AnalogWaveform<double>:
AnalogWaveform<double> result = AnalogWaveform<double>.FromArray1D(data.Samples);
result.Timing = WaveformTiming.CreateWithIrregularInterval(data.Timing);
result.ChannelName = signal.Alias;
result.UnitDescription = signal.UnitOfMeasurement;
The TDMS file is saved after each call to AppenAnalogWaveform.
What is really funny is that the docs for TdmsFile.Dispose() says:
Call Dispose when you are finished using the TdmsFile. The Dispose method closes the TDMS file, and leaves it in an unusable state. This method does not save the file. Call Open to re-open the TDMS file.
If dispose really leaves the file unusable (sic!) it is great that you have documented it. 😉
