Flow control mechanism of WIZnet serial to ethernet module

jameskim · 2013-10-21T14:13:42+09:00

Recently, I got a question from one of customers. That is what they found out WIZ107SR’s flow control has something wrong while evaluating it. As a result, I can say that WIZ107SR’s flow control works well but they had a different expectation. Below is their network configuration for test. Working scenario is like below. When one activates RTS signal of Computer A, it informs that Computer A has no buffer for data from WIZ107SR A. Then, WIZ107SR A doesn’t send any data received from its peer, WIZ107SR B, to Compter A via Serial I/F. (Decreasing windows size of WIZ107SR A shows that RTS/CTS flow control of WIZ107SR works well) But, WIZ107SR A has 2KB Rx data buffer inside its TCP/IP core logic so it accepts data from WIZ107SR B and stores it into its internal buffer. It means that Computer B can send data to WIZ107SR A via WIZ107SR B, even though Computer A activated RTS signal to inform that it has no room to store data. However, data which Computer B sent isn’t lost because WIZ107SR A stores it in its internal buffer. If one deactivates RTS signal of Computer A then all data which stored in Rx buffer of WIZ107SR A will be transferred to Computer A. And to conclude, WIZ107SR’s RTS/CTS Flow control works well under the condition which we designed. With above network configuration, if ones want for Computer B not to send any data while Computer A activates RTS signal, then that is not WIZnet’s design goal. If someone wants that Computer B knows it instantly when Computer A activates RTS signal, then it’s an customization issue. Thank you. James.

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