Re: [lwip-users] TM4C1294 LWIP Usage

[Lee Noack]

Hi Noam,

I would probably call it a data server. Is it not possible to start writing in either direction once the connection is established? Thank you for the code I shall look at it today.  I'm not quite with you. If the data I wish to send is the maximum size of the payload of a packet, there should be nothing to queue so it should just be sent immediately??

Lee.

On Fri, Dec 19, 2014 at 1:37 AM, Noam weissman <address@hidden> wrote:

Hi Lee,

You are talking on a client application. That's a bit different.

Yes you are correct you do not need to use recvd but you must use the
tcp_sent callback to be able to know when to send more.
You can also check the amount of RAM left in the sent queue so you can
send and send until you are on the limit, then wait for
the tcp_sent to fire...

All my code are servers so I do not have something on hand that can
help.

Here is one of my functions that I use. Instead of calling tcp_write
directly I took something from one of the examples I so:

static err_t  my_write(struct tcp_pcb *pcb, const void* ptr, u16_t
*length, u8_t apiflags)
{
   u16_t len;
   err_t err;
   len = *length;

   do
   {
     err = tcp_write(pcb, ptr, len, apiflags);

     if(err == ERR_MEM)
     {
       if((tcp_sndbuf(pcb) == 0) || (pcb->snd_queuelen >=
TCP_SND_QUEUELEN))
       {
         /* no need to try smaller sizes */
         len = 1;
       }
       else
       {
         len /= 2;
       }
     }
    else
    {
       // if we are here it means that we have a timeout or
       // network error and need to abort
    }

   }  while ((err == ERR_MEM) && (len > 1));

   *length = len;

   return err;
}


In the above code you try to send as much as you can and if tcp send
buff is too small you try to send less and less, until you are
successful or not.
If you are not able to send everything you must wait for data buffers to
get freed. This is done by calling the above code inside the tcp_sent
call back

Do not expect high throughput from LwIP. It is small but not very fast.
I have read people are able to run it at about 1Mb, maybe I am wrong.

BR,
Noam.




-----Original Message-----
From: lwip-users-bounces+noam=address@hidden
[mailto:lwip-users-bounces+noam=address@hidden] On Behalf Of Lee
Sent: Thursday, December 18, 2014 11:40 AM
To: address@hidden
Subject: Re: [lwip-users] TM4C1294 LWIP Usage

Hi Noam,

No I am not using an RTOS. I managed to echo characters today so that
was a step forward. I was using a fairly simple and easy to understand
tcp_echo code. tcp_echo_2.c
<http://lwip.100.n7.nabble.com/file/n23627/tcp_echo_2.c>

However my goal is not to receive but only to send. So  i won't need to
use the recvd function and  then tcp_write(),tcp_sent() to loopback.
Once I have a connection I will only need to write. I should be able to
DMA in my data into 2 large buffers (maybe 1400 Bytes each) and then
call a tcp_write with a pointer to this buffer. Then when my other
buffer is full, call a tcp_write with a pointer to this buffer.

I understand what you are saying about the code getting held up with
lack of acks and freeing of buffers but I'm hoping the data will be fed
out the ethernet faster than the data is coming in.

The data will be coming in at 2.4MB/s so I'm not hopeful I can achieve
the throughput with 100Mb/s ethernet.


First problem though is using the tcp_write() outside of the recvd
callback.
Hopefully I can just go something like that which is attached but in a
write function.

tcp_write( pcb, my_buffer, 1400, 0 );
tcp_sent( pcb, NULL );

I'm not sure that I can use the pcb that I accepted with though.






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