How many elements has @datapoints after the while loop? I don't know if there are more errors, but maybe one problem is in the line:

@datapoint = splice(@values, 0, $x);
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After the while loop @datapoint will only have the last value unpacked, you should use push @datapoint, splice(@values,0,$x) instead

Also, taking into account that unpack called in scalar context returns only the first element unpacked, you can just simply write

push @datapoint, unpack ("V",$buf)
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Update (thanks to moritz):

push @datapoint, scalar unpack ("V",$buf)
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Hope this helps

citromatik