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= WARPLab: Sample Buffer Sizes  =

In WARPLab 7.4 and earlier, all transmit and receive samples were stored in buffers of BRAM directly on the FPGA. As of WARPLab 7.5 these samples are buffered in the BRAM but stored in the DRAM SODIMM attached to the WARP v3 hardware.

|| ||=  '''WARPLab 7.4'''  =||=  '''WARPLab 7.5 (4RF)'''  =||=  '''WARPLab 7.5 (2RF)'''  =||
|| Tx max samples  ||  32 kSamp  ||  56 MSamp  per interface ||  112 MSamp per interface ||
|| Tx max duration at 40MHz sampling  ||  819.2 µsec  ||  1.468 sec  ||  2.9360 sec  ||
|| Rx max samples  ||  32 kSamp  ||  64 MSamp per interface ||  128 MSamp per interface ||
|| Rx max duration at 40MHz sampling  ||  819.2 µsec  ||  1.6777 sec  ||  3.3554 sec  ||

The table above summarizes the maximum buffer sizes for the WARPLab 7.5 design. Since the buffer space is divided among RF interfaces, the 2RF design can store more samples than the 4RF design. WARPLab 7.5 maintains full backward compatibility with WARPLab 7.4, so all existing scripts compatible with WAPRLab 7.4 will "just work" with the new design and will use the existing WARPLab 7.4 limitations on buffer sizes.

== Performance Considerations ==

With all of the extra buffer space that the hardware design is capable of, the chief limitation on usable buffer sizes shifts burden to the user's PC. Each sample is represented as a complex double precision floating point number in a MATLAB, occupying 16 bytes in memory.

The table below shows the storage size of various sample vectors, up to the new maximum vector lengths in WARPLab 7.5. Note these sizes are how much RAM is required to store each vector in the MATLAB workspace. Retrieving the vector and processing the vector requires additional RAM. Depending on the amount of RAM on the host PC and what other programs are currently running, a user should limit the number of samples they are working with to stay under the total available memory. If MATLAB's memory utilization rises too far, it is common that the MATLAB application will stall while the OS swaps memory to disk. On Windows the MATLAB {{{memory}}} command will summarize the available RAM and largest supported array size in your MATLAB instance.

||=  Sample Vector Length =||=  Occupied Memory =||
|| 32 kSamp  || 512 kByte  ||
|| 256 kSamp  || 4 MByte  || 
|| 2 MSamp  || 32 MByte  || 
|| 16 MSamp  || 256 MByte  || 
|| 128 MSamp  || 2 GByte  || 


One thing to note is that these are steady state memory figures for a request of a single interface.  Peak memory usages may be greater than this due to some copying of data between structures during fetches from the transport.  

In WARPLab 7.5.0, due to the way the transport processes samples:
   Steady state memory usage = (Num Interfaces) * (Occupied Memory for the Sample Vector Length)
   Peak memory usage = (Num Interfaces + 1) * (Occupied Memory for the Sample Vector Length)

For example, we we were trying to capture 2^25^ samples (ie 32 MSamples) for 4 interfaces, this would have a steady state memory usage of 2 GBytes (ie 4 Interfaces * 512 MBytes / Interface) and a peak memory usage of 2.5 GBytes (ie 5 Interfaces * 512 MBytes / Interface).