User`s guide

System Concepts
1-13
Data Buffers and Transferring Data
At each sample interval of the real-time application, Simulink stores
contiguous data points in memory until a data buffer is filled. Once the data
buffer is filled, Simulink suspends data capture while the data is transferred
back to MATLAB through Simulink external mode. Your real-time application,
however, continues to run. Transfer of data is less critical than maintaining
deterministic real-time updates at the selected sample interval. Therefore,
data transfer runs at a lower priority in the remaining CPU time after model
computations are performed while waiting for another interrupt to trigger the
next model update.
Data captured within one buffer is contiguous. When a buffer of data has been
transferred to Simulink, it is immediately plotted in a Simulink Scope block, or
it can be saved directly to a MAT-file using the data archiving feature of the
Simulink external mode.
With data archiving, each buffer of data can be saved to its own MAT-file. The
MAT-filenames can be automatically incremented, allowing you to capture and
automatically store many data buffers. Although points within a buffer are
contiguous, the time required to transfer data back to Simulink forces an
intermission for data collection until the entire buffer has been transferred and
may result in lost sample points between data buffers.