Re: [lwip-users] tcp_connection (no SYN packet on server side)

[Inderjit Singh]

delay_ms is used throughout our bare metal implementation I can guarantee it's 
not blocking.
tcp_cb_called is called to the registered callback function yes. And sure, main 
loop as you suggest is functional as well yes. 
However I fail see why LWIP layer marks SYN_SENT state in pcb but I cannot see 
the packet's being transmitted/received on the datalink itself? LWIP doesn't 
signal any failures has been made during the process except the abort at error 
callback when the timeout is reached. 

________________________________________
From: lwip-users address@hidden on behalf of Sergio R. Caprile address@hidden
Sent: 04 June 2018 16:58
To: address@hidden
Subject: Re: [lwip-users] tcp_connection (no SYN packet on server side)

That may or may not work depending on what your _magic function_
"delay_ms" does. If it is blocking, you are busted.

A main loop is a main loop, you need to rx and you need to check
timeouts. Your accept callback will be called after the SYN is SYNACKed
and the SYNACK is ACKed back. For that, you need to have the stack
running, otherwise no one can send anything, and that is done by calling
sys_check_timeouts() as frequently as you can. And you need to rx for
the SYNACK, which is done by calling ethernetif_input() frequently
enough in order not to lose frames. That can't happen if you are blocking.

If you really want to sequentially check for whatever reason, you can do
this:

udp_cb_called = tcp_cb_called = false;

IP4_ADDR(&ip, ETH_CONF_IPADDR0, ETH_CONF_IPADDR1, ETH_CONF_IPADDR2, 155);
err = tcp_connect(pcb_tcp, &ip, ETH_TCP_PORT_REM, tcp_connected_cb);
if (err != ERR_OK) {
        // Oops
}

while(udp_cb_called == false && tcp_cb_called == false) {
        ethernetif_input(&dev_netif);
        sys_check_timeouts();
}

Your second attempt to call connect will fail as your pcb is being used,
so that won't work inside a loop (and a bit involved to explain in one
line). And I guess you'll set tcp_cb_called to "true" somewhere in your
tcp_connected_cb()

However, that is not much different from a real main loop:

while(1) {
        ethernetif_input(&dev_netif);
        if(whatiamexpectinghashappened)
                ; // bingo!
        sys_check_timeouts();
        world_save();
        stuff_do();
        morestuff_moredo();
}


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