Assuming sender block uses clk1, while receiving block uses clk2. Sender block and receiving block use 4-phase REQ-ACK protocol for clock domain crossing.

Also assume the sender block interacts with its upstream logic using valid-ready protocol, and the receiving block interacts with its downstream logic using valid-ready protocol.

Obviously, 4-phase REQ-ACK protocol is slower than 2-phase REQ-ACK protocol, since each transfer involves 4 signal transitions compared to 2 signal transitions.

However, 4-phase REQ-ACK protocol is more robust than 2-phase REQ-ACK protocol. We will explain the reason in next post.


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