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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