How to efficiently create an array of libpointers?
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Pico Technology
on 1 Oct 2013
Commented: Pico Technology
on 7 Oct 2013
Hi,
I am working on a piece of code to create a 2D array of libpointers that can be passed to a shared library. This corresponds to dividing up the memory on a device to capture data for each channel on a device:
nCaptures = 2000000;
num_samples = 64;
tic;
for ch = 1:4
for segment = 1:nCaptures
if(channelSettings(ch).enabled)
rapidBlockBuffer(ch, segment) = libpointer('int16Ptr', zeros(num_samples, 1));
[status.setDataBufferBulk(ch, segment)] = calllib('PS6000', 'ps6000SetDataBufferBulk', handle, ch - 1, ...
rapidBlockBuffer(ch, segment), num_samples, segment - 1, downSampleRatioMode);
else
rapidBlockBuffer(ch, segment) = libpointer('int16Ptr', 0);
end
end
end
toc;
On a Windows 8 64-bit PC with MATLAB 2012b, this code was running for well over 1.5 hours and hadn't completed.
Is the else condition a suitable way of maintaining the array dimensions if a channel on the device is not enabled?
Thanks,
H
Accepted Answer
Philip Borghesani
on 2 Oct 2013
Edited: Philip Borghesani
on 2 Oct 2013
The libpointer code itself is fine but if you did not preallocate rapidBlockBuffer then this code is very slow (order n^2 instead of order n). I added
rapidBlockBuffer(4,nCaptures)=libpointer;
before the ch for loop and find the code without the calllib call will complete in a few minutes. If status.setDataBufferBulk is not preallocated then it should also be.
When rapidBlockBuffer is prealloced there is no need for the else block inserting a dummy pointer.
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