100m write data, 133m receive data, see the fifo used for processing synchronization on the book, that is, the number of writes used is compared with the number of reads after synchronization, if it is equal to 0, an empty signal is generated, indicating the current data in the fifo Read it all. The synchronization is the synchronization of the two registers used. My question is why synchronization can be achieved by doing this, and how is synchronization achieved? I still don't understand clock synchronization, thank you. . .