The performance of simple socket server

I have done the same. Since you probably do not send packets both ways (mostly TO the board), lwip waits for outgoing packets for some time before it ACKs a packet. You need to change the timeout for this counter, and you should also send an immediate reply for each packet.

Do the following in \altera\kits\nios2\components\altera_lwip\UCOSII\src\downloads\lwip-0.6.3\src\api\tcp.h:

# define TCP_FAST_INTERVAL 100

You should try other values as well.

Also, in tcp.c, change tcp_recved() to:

void

tcp_recved(struct tcp_pcb *pcb, u16_t len)

{

int ackNow=0;

if ((u32_t)pcb->rcv_wnd + len > TCP_WND) {

pcb->rcv_wnd = TCP_WND;

} else {

pcb->rcv_wnd += len;

ackNow=1;

}

if (!(pcb->flags & TF_ACK_DELAY) &&

!(pcb->flags & TF_ACK_NOW)) {

/*

* We send an ACK here (if one is not already pending, hence

* the above tests) as tcp_recved() implies that the application

* has processed some data, and so we can open the receiver's

* window to allow more to be transmitted. This could result in

* two ACKs being sent for each received packet in some limited cases

* (where the application is only receiving data, and is slow to

* process it) but it is necessary to guarantee that the sender can

* continue to transmit.

*/

tcp_ack(pcb);

}else if((pcb->flags & TF_ACK_DELAY)&&(ackNow)){

//++cg[11/10/2004]: I think this is what Atte Kojo was talking about

tcp_ack(pcb);

}

}