WIZ550SR data buffering at small gap between messages

Question

Hello, I’m using the WIZ550SR Module to exchange data between a PC and multiple microcontrollers (each with it’s own WIZ550SR in server mode). The communication and everything else works fine, however I have an issue with the received data (from PC to microcontroller via the module), if the data is sent with small time gap between. If the gap between the messages is >200ms everything is fine. The module sends the data every 200ms. However the minimal gap between the data from PC to the module ist about 15-20ms. The data contains 3-5 Bytes. The module is not sending the data right away. The data seems to be buffered and is sent out every 200ms. Since the microcontroller has to react according to the data received (at a certain time), there is a chance that the microcontroller hasn’t received the data but has to trigger some outputs according to the data. Is there any setting I can change to prevent the module to buffer the data and transmit it imidiatly? Or at least reduce this buffer time?

Ricky · Answer

Dear, PKalen Both serial to ethernet and ethernet to serial process data by polling. In other words, data is delivered immediately. The cause of delay can occur when searching for AT command trigger code or when packing data. Disable At Command. And please do not use packing condition.

PKalen · Answer

Hello Ricky, thank you for your answer. I checked my settings and tried a few things, however I still have that delay. Here are my settings: Settings848×705 82.9 KB I logged the communication with Hterm. I used the Evaluation Board WIZ550SR EVB to monitor the data sent out via uart. Additionally I watched the transmitted data with a scope. I made a minimal TCP Client Application running on my PC. I’m sending two bytes from “p0” counting up to “p9” and then again from “p0”… Everything above 200ms it send out immidiatly. Below 200ms I have that delay/buffering. Here are some Logs from Hterm: Logs.zip (69,3 KB) The AT commands and packing is disabled. Since I send out 2 Bytes I triedthe same with the Size 2 in Packing Conditions without any changes. Are my settings correct? Is there anything else I could do?

PKalen · Answer

Hello Ricky, again, thank you for your time helping me out. I tried a lot of different settings: limit the size to 2 adding delimiters used a time limit combinations from above with no changes… The description of the packing conditions mentions UART to Ethernet all the time. But is this valid for the data the other direction (Ethernet to UART)? Because I have this issue from Ethernet to UART, if I send data continiously from my PC (Client) to the Module (Server) every <200ms it does that buffering.

PKalen · Answer

Hello Ricky, I got myself a WIZ850io, hooked it up to a STM32 NUCLEO board and built my own TCP(server) to UART application to test the issue. I used the ioLibrary (w550.c/h, socket.c/h and wizchip_conf.c/h). First I had the same behavior. Everything send to the w5500 with less than 200ms wouldn’t be send immidiatly. I then searched anything indicating to that delay. There is a define RTR in the w5500 header. The description says: “And so the default timeout period is 200ms(100us X 2000). During the time configured by @ref RTR, W5500 waits for the peer response to the packet that is transmitted by \ref Sn_CR (CONNECT, DISCON, CLOSE, SEND, SEND_MAC, SEND_KEEP command).” If a socket has been opend, this timeout period will be used all the time. Except if the socket is opened with “SF_TCP_NODELAY” as the socket flag parameter of the socket() function. Checking the source code of the WIZ550SR the socked gets opend whith: socket(sock, Sn_MR_TCP, net->local_port, SF_IO_NONBLOCK); Therefor the timeout period is used. Since I can measure the 200ms timeout I guess the WIZ550SR does not chnage the RTR value?! With my test setup, before opening the socket with SF_NON_BLOCKING flag I set the timeout to 1 (=100µs). The data will be sent out immidiatly (almost, 100µs delay is still there). Changing the open socked parameters to (…, “SF_TCP_NODELAY”) without changeing the RTR value, data will be send immidiatly. However the socket is no more non-blocking. I’m not sure what will be the best setting for me (have to test this). Since the socket open is hard-coded with SF_NON_BLOCKING, there is no option to change it to SF_TCP_NODELAY without changes to the firmware. But is there a way to change the RTR value without changeing the firmware of the WIZ550SR?

PKalen · Answer

Hello Ricky, if you could change the opening socket with SF_TCP_NODELAY so I can test it. This would be very helpful.

PKalen · Answer

Hello Ricky, thank you for the firmware. I don’t know if I have the time to test it this week. However I will notify you with the results.

PKalen · Answer

Hello Ricky, I flashed the module with your firmware. After that the modul isn’t doing anything. No green led blinking, nor any reply from both serial interfaces. Can I simply programm your binary with the ST tool? I did this with several moduls and firmware 1.1.7 and didn’t have any issue.