How do you import LABVIEW time stamps into MATLAB
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Benjamin Dolgin
il 27 Gen 2016
Commentato: Walter Roberson
il 14 Dic 2016
Bug in h5info.
Command
gr_inf=h5info(f_name, '/wfm_group0/axes/axis0' );
Produces an error:
Warning: There is no MATLAB integer type that corresponds to an HDF5 integer type with 16 bytes. The
data will be treated as an uninterpreted uint8 array.
> In h5info (line 74)
In read_scope_hws (line 17)
The file that is being read was created by the NI oscilloscope program.
Not surprisingly, a later statement
ref_time1=gr_inf.Attributes(9).Value;
produces an array of 16 two-byte int8 numbers instead of a 64 byte integer.
The problem is not due to not understanding which group or which attribute to read; the information in Attributes(9).Value is a time stamp. It is just that MATLAB and LABVIEW creators are not talking to each other. The file in question contains four time stamps; each produces a warning.
Does anybody know how to either:
1. Fix the bug in h5info.m
2. How to covert the received 64 bytes in a time stamp by hand
4 Commenti
dpb
il 27 Gen 2016
Modificato: dpb
il 27 Gen 2016
http://www.ni.com/tutorial/7900/en/ says "The LabVIEW timestamp is a 128-bit data type...". That's 16-bytes which is what the hfinfo call thought was there. I don't see that the NI doc actually states about endianess, that would be an issue.
There's also the issue of whether it's Gregorian or Julian calendar as I note one respondent had issues with the Gregorian as claimed in the above link.
I was asking if you can't provide the actual 16 bytes returned and do you know what the answer is supposed to be?
I always loved NI hardware but detested their software libraries...I've not used any of their gear nor LABVIEW in over 20 years now...and can't says as how's I've missed it! :)
dpb
il 27 Gen 2016
Modificato: dpb
il 27 Gen 2016
OK, messing around w/ the example on the NI page, if I take their third example of fractional seconds of a string of '0xCCCCCCCCCCCCCCCD'
>> c='CCCCCCCCCCCCCCCD'; % ML character representation
>> atto=sscanf(c,'%lx') % the atto-seconds field
atto =
14757395258967641293
>> magn=uint64(2^64); % max 64-bit integer
>> f=double(atto)/double(magn) % convert to decimal (approx)
f =
0.8000
>>
That is what they say the value is after the 54 seconds in 12/31/1903 23:59:54.800.
If you've got the 16 bytes you're almost there it would seem.
Risposta accettata
Benjamin Dolgin
il 29 Gen 2016
Modificato: dpb
il 12 Feb 2016
5 Commenti
Guru Subramani
il 14 Dic 2016
"Time stamp actually consists of two int64; the first one is signed the second is unsigned " - Benjamin Dolgin, I think this describes what is going on clearly. Thanks!
Walter Roberson
il 14 Dic 2016
"MATLAB h5info has a bug: it does not recognize int128 variables"
That is not a bug. MATLAB does not have any int128 data type. It is a limitation. To handle int128 or uint128, Mathworks would have to create a complete extended-precision software mathematics facility: all other calculations in basic MATLAB are done with hardware instructions, but the x64 instruction set does not offer 128 bit integer operations.
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