Re: [lwip-users] TCP behaviour with Zero Copy API using Raw API interface

[Peter Jolasson]

Hi,

My problem was the lwip_standard_chksum() routine in the inet.c module.
I wasn't aware that it might need to be rewritten/ported. (I don't
remember seeing it in any documentation.)

I just included a compile directive when MEM_ALIGNMENT >= 2.
Maybe this could/should be put into the code repository?

//Peter



static u16_t
lwip_standard_chksum(void *dataptr, int len)
{
  u32_t acc;

  LWIP_DEBUGF(INET_DEBUG, ("lwip_chksum(%p, %d)\n", (void *)dataptr, len));
  for(acc = 0; len > 1; len -= 2) {
      /*    acc = acc + *((u16_t *)dataptr)++;*/
#if MEM_ALIGNMENT >= 2
    acc += htons( ((u16_t)(((u8_t *)dataptr)[0])<<8) | ((u8_t *)dataptr)[1] );
    dataptr += 2;
#else
    acc += *(u16_t *)dataptr;
    dataptr = (void *)((u16_t *)dataptr + 1);
#endif
  }

  /* add up any odd byte */
  if (len == 1) {
    acc += htons((u16_t)((*(u8_t *)dataptr) & 0xff) << 8);
    LWIP_DEBUGF(INET_DEBUG, ("inet: chksum: odd byte %d\n", (unsigned
int)(*(u8_t *)dataptr)));
  } else {
    LWIP_DEBUGF(INET_DEBUG, ("inet: chksum: no odd byte\n"));
  }
  acc = (acc >> 16) + (acc & 0xffffUL);

  if ((acc & 0xffff0000) != 0) {
    acc = (acc >> 16) + (acc & 0xffffUL);
  }

  return (u16_t)acc;
}





On 6/8/05, Bill Knight <address@hidden> wrote:
> This is possibly a problem with the ip checksum routine running
> on a 16 or 32 bit cpu.
> 
> Regards
> -Bill Knight
> R O SOftWare &
> http://www.theARMPatch.com
> 
> 
> 
> On Wed, 8 Jun 2005 10:46:29 +0200, Peter Jolasson wrote:
> 
> >Hi again,
> 
> >To correct myself.
> >It's not when there is an odd number of bytes to transfer that it fails.
> >It fails when the data is located at an odd address.
> 
> >But as said before my workaround is to set "copy" to 1 and then it works OK.
> 
> >My target cpu is ARM and I've set MEM_ALIGNMENT to 4.
> >//Peter
> 
> >On 6/8/05, Peter Jolasson <address@hidden> wrote:
> >> Hi,
> >>
> >> I dont have a solution to your problem but I can describe a 'funny' 
> >> behavior
> >> that I've noticed with tcp_write().
> >> When I send an even number of bytes I can set "copy" to 0.
> >> But when sending an odd number of bytes I must set "copy" to 1 otherwise
> >> it will fail.
> >>
> >> I'm using lwIP 1.1.0
> >> //Peter
> >>
> >> On 6/7/05, Sathya Thammanur <address@hidden> wrote:
> >> > Hi all,
> >> > I have a client program that connects to a server on PC. The client is
> >> > a simple program that sends data to PC. What I notice is that when I
> >> > call  tcp_write() with "copy" argument 1, then my program works
> >> > without any issues. However, if I change "copy" to 0 then I notice
> >> > that the TCP connection is not established completely. The following
> >> > happens :
> >> >
> >> > Client                            Server
> >> > SYN ---------->
> >> >       <---------             SYN, ACK
> >> >
> >> > Junk packet sent from client. The Server resends the SYN, ACK and then
> >> > closes the connection. TCP client sends a lost ACK with incorrect
> >> > sequence number after couple of junk packets.
> >> >
> >> > I do notice that my application call back that is registered with
> >> > tcp_connected() is called. Here is where I start to send data. I am
> >> > using lwip version 0.7.2.  Am I using the tcp_write() in the right way
> >> > as intended ? Any correct usage of this function will be very useful.
> >> >
> >> > Any help would be greatly appreciated.
> >> >
> >> > Thanks,
> >> > Sathya
> >> >
> >> >
> >> > _______________________________________________
> >> > lwip-users mailing list
> >> > address@hidden
> >> > http://lists.nongnu.org/mailman/listinfo/lwip-users
> >> >
> >>
> 
> 
> >_______________________________________________
> >lwip-users mailing list
> >address@hidden
> >http://lists.nongnu.org/mailman/listinfo/lwip-users
> 
> 
> 
> 
> 
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