Re: [lwip-users] RAW - tcpip_callback causes delays

[address@hidden]

From reading the code, the cause of the delay is that you don't call 
tcp_output() after calling tcp_write(). tcp_write() only enqueues 
without sending. The data is then sent later by a TCP timer (which is 
the reason for the relatively exact delay of 200 ms). (BTW: Variant 2 is 
the correct way, you don't need to use tcp_callback).

Simon


ncoage wrote:
> Hi,
>
> I'm having troubles with tcp server based on RAW API. I'm using tcpip_callback 
> function, which causes delays (about 200ms). When I call directly tcp_write 
> function everything is ok (no delays). I wrote simple server to illustrate my 
> problem:
>
> // -----------------------------------------------------------------
> #include "lwip/opt.h"
> #include "lwip/mem.h"
> #include "lwip/tcp.h"
> #include "lwip/tcpip.h"
>
> void tcpSendReply(void *ctx)
> {
>         unsigned char data[10] = "REPLY!!!\r\n";
>         struct tcp_pcb *pcb = ctx;
>         tcp_write(pcb, data, sizeof(data), TCP_WRITE_FLAG_COPY);
> }
>
> err_t callbackServerRecv(void *arg, struct tcp_pcb *pcb, struct pbuf *p, err_t 
> err)
> {
>         if (err == ERR_OK && p != NULL)
>         {
>                 tcp_recved(pcb, p->tot_len);
>
>                 // Variant 1
>                 //tcpip_callback_with_block(tcpSendReply, pcb, 0);
>                 // Variant 2
>                 tcpSendReply(pcb);
>
>                 pbuf_free(p);
>         }
>         else if (err == ERR_OK && p == NULL)
>         {
>                 tcp_close(pcb);
>         }
>         return ERR_OK;
> }
>
> err_t callbackServerAccept(void *arg, struct tcp_pcb *newpcb, err_t err)
> {
>         tcp_recv(newpcb, callbackServerRecv);
>         return ERR_OK;
> }
>
> void callbackServerInit()
> {
>         struct tcp_pcb *pcb;
>         pcb = tcp_new();
>         tcp_bind(pcb, IP_ADDR_ANY, 9923);
>         pcb = tcp_listen(pcb);
>         tcp_accept(pcb, callbackServerAccept);
> }
> // -----------------------------------------------------------------
>
> It will be great if someone could test this server and check results in 
> Wireshark (Variant 1 and 2 - see code). All you need to do is paste above code 
> to your project and call callbackServerInit() function. Then on PC run 'telnet 
> x.x.x.x 9923'. Server replies when you type any character.
>
> I attach Wireshark capture files (Variant 1 i 2).
>
> Best regards
> ------------------------------------------------------------------------
>
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