I have setup a Wiznet 5500 module as a simple TCP client on an STM32G0B1KET6.
Here are the two snippets which make the connection to the server as well as create the socket.

bool connectSocket()
{
    int8_t sockret=socket(1,Sn_MR_TCP,80,0);
    if(sockret==1)
    {
        Send_UART1("SOCKET OKrn");
        return true;
    }
    else
    {
        Send_UART1("SOCKET failedrn");
        return false;
    }
}

bool connectServer()
{
    int8_t ret=connect(1, destination_ip, destination_port);
    if(ret==SOCK_OK)
    {
        Send_UART1("TCP connectedrn");
        return true;
    }
    else
    {
        char err[32];
        memset(err,0,32);
        sprintf(err,"TCP not connected-%irn",ret);
        Send_UART1(err);
        return false;
    }
}

void sendTCP(uint8_t * msg,uint16_t len)
{
    int32_t  x=send(1,msg,len);
    char snt[20];
    memset(snt,0,20);
    sprintf(snt,"SENT:%lirn",x);
    Send_UART1(snt);

}

void readTCP(uint8_t * msg,uint16_t len)
{
    int32_t  x=recv(1,msg,len);
    char snt[20];
    memset(snt,0,20);
    sprintf(snt,"RCV:%lirn",x);
    Send_UART1(snt);
}

I can connect to the Module and make a GET request.
I can make a send() to the Server successfully.
I can make an initial recv() successfully.
I can write a second time to the server.
Up until this point the getSn_SR(1) returns 0x17 (SOCK_ESTABLISHED)
But, on the second recv() the socket getSn_SR(1) returns 0x00 (SOCK_CLOSED)

Any help would be appreciated!

I have literally tried everyhting, to no avail. This is just some notes on my attempts.

• The second write is identical to the first write. So I dont think its a error in the GET request.
• The GET request has a keep-open conn status
• I can do the same GET request using a C# app I wrote and the server answers every time.
• I am convinced I havent got the correct values in the int8_t sockret=socket(1,Sn_MR_TCP,80,0); call. But finding the correct documentation is a quagmire on the wiznet website.