Re-TX data on the W5500

Question

All, I have been re-writeing the iolibrary_v100 for the processor I am using. I was going through the TCPReSend function, in particular TCPReSendNB(). After some checks, it issues the SEND command in the sockets CR register. Here is what I am wondering. If the SEND command was already used to on the first transmit, TCPSend. Then would not the TX_RD and TX_WR be the same value? And if so, how does sending the SEND command again work, if the TX_RD and TX_WR are the same value? If one could decrease the TX_RD by the data length, then I could see resending the SEND command work. But the TX_RD is read only, correct? So if it is read only, then how can data be re-transmitted without loading the data back into the socket TX buffer first, and increasing the TX_WR pointer? Thanks, Jim

JimMartz · Answer

I think I figured it out. The only thing in the W5500 datasheet says is “SEND command transmits from the current Sn_TX_RD to the Sn_TX_WR”. Well looking at the datasheet for the W5200(page 50) it looks like there is an exception to that. If the data is longer then what is set in the MSS register, then it only sends that length of data. In that case the Sn_TX_RD would not be increased all the way to Sn_TX_WR and the resend fiction TCPReSend would be the thing to use to transmit the next chunk of data. The whole section 5 of the W5200 data sheet is missing from the W5500 manual, I hope this gets included in the W5500 datasheet for people like me that have not used a previous wiz chip. Thanks, Jim