(1) selected.gtkw is modified to ease the browse of waveform.
(2) testbench.v is modified to adopt the debugging of memory_bank.v.
(3) memory_bank.v is modified and verified, the functionality seems to been correct.
(4) free_buffer_tracker.v is reimplemented to make it work correctly. We modified the FIFO implementation.
We add lots of comment in the packet_source.v.