Volk memory alignement for signal vectors was using a hardcoded 16 bytes
value. This parameter is machine-dependant and thus, in modern machines
caused memory exceptions if the parameter not match.
All posix_memalign functions are now replaced by the GNU Radio
volk_malloc(vector_size (bytes), volk_get_alignement());
volk_get_alignement() returns the number of bytes to align the memory
blocks in the current processor.
The memory bug showed up when the receiver is configured with higher
sample rates (>4 Msps!)
