mprio = TCP_PRIO_MAX;
  
  /* We kill the oldest active connection that has lower priority than
     prio. */
  inactivity = 0;
  inactive = NULL;
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    if (pcb->prio <= prio &&
       pcb->prio <= mprio &&
       (u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
      inactivity = tcp_ticks - pcb->tmr;
      inactive = pcb;
      mprio = pcb->prio;
    }
  }
  if (inactive != NULL) {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_prio: killing oldest PCB %p (%ld)\n",
           (void *)inactive, inactivity));
    tcp_abort(inactive);
  }      
}


static void
tcp_kill_timewait(void)
{
  struct tcp_pcb *pcb, *inactive;
  u32_t inactivity;

  inactivity = 0;
  inactive = NULL;
  for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
    if ((u32_t)(tcp_ticks - pcb->tmr) >= inactivity) {
      inactivity = tcp_ticks - pcb->tmr;
      inactive = pcb;
    }
  }
  if (inactive != NULL) {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_kill_timewait: killing oldest TIME-WAIT PCB %p (%ld)\n",
           (void *)inactive, inactivity));
    tcp_abort(inactive);
  }      
}



struct tcp_pcb *
tcp_alloc(u8_t prio)
{
  struct tcp_pcb *pcb;
  u32_t iss;
  
  pcb = memp_malloc(MEMP_TCP_PCB);
  if (pcb == NULL) {
    /* Try killing oldest connection in TIME-WAIT. */
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_alloc: killing off oldest TIME-WAIT connection\n"));
    tcp_kill_timewait();
    pcb = memp_malloc(MEMP_TCP_PCB);
    if (pcb == NULL) {
      tcp_kill_prio(prio);    
      pcb = memp_malloc(MEMP_TCP_PCB);
    }
  }
  if (pcb != NULL) {
    memset(pcb, 0, sizeof(struct tcp_pcb));
    pcb->prio = TCP_PRIO_NORMAL;
    pcb->snd_buf = TCP_SND_BUF;
    pcb->snd_queuelen = 0;
    pcb->rcv_wnd = TCP_WND;
    pcb->tos = 0;
    pcb->ttl = TCP_TTL;
    pcb->mss = TCP_MSS;
    pcb->rto = 3000 / TCP_SLOW_INTERVAL;
    pcb->sa = 0;
    pcb->sv = 3000 / TCP_SLOW_INTERVAL;
    pcb->rtime = 0;
    pcb->cwnd = 1;
    iss = tcp_next_iss();
    pcb->snd_wl2 = iss;
    pcb->snd_nxt = iss;
    pcb->snd_max = iss;
    pcb->lastack = iss;
    pcb->snd_lbb = iss;   
    pcb->tmr = tcp_ticks;

    pcb->polltmr = 0;

#if LWIP_CALLBACK_API
    pcb->recv = tcp_recv_null;
#endif /* LWIP_CALLBACK_API */  
    
    /* Init KEEPALIVE timer */
    pcb->keepalive = TCP_KEEPDEFAULT;
    pcb->keep_cnt = 0;
  }
  return pcb;
}

/**
 * Creates a new TCP protocol control block but doesn't place it on
 * any of the TCP PCB lists.
 *
 * @internal: Maybe there should be a idle TCP PCB list where these
 * PCBs are put on. We can then implement port reservation using
 * tcp_bind(). Currently, we lack this (BSD socket type of) feature.
 */

struct tcp_pcb *
tcp_new(void)
{
  return tcp_alloc(TCP_PRIO_NORMAL);
}

/*
 * tcp_arg():
 *
 * Used to specify the argument that should be passed callback
 * functions.
 *
 */ 

void
tcp_arg(struct tcp_pcb *pcb, void *arg)
{  
  pcb->callback_arg = arg;
}
#if LWIP_CALLBACK_API

/**
 * Used to specify the function that should be called when a TCP
 * connection receives data.
 *
 */ 
void
tcp_recv(struct tcp_pcb *pcb,
   err_t (* recv)(void *arg, struct tcp_pcb *tpcb, struct pbuf *p, err_t err))
{
  pcb->recv = recv;
}

/**
 * Used to specify the function that should be called when TCP data
 * has been successfully delivered to the remote host.
 *
 */ 

void
tcp_sent(struct tcp_pcb *pcb,
   err_t (* sent)(void *arg, struct tcp_pcb *tpcb, u16_t len))
{
  pcb->sent = sent;
}

/**
 * Used to specify the function that should be called when a fatal error
 * has occured on the connection.
 *
 */ 
void
tcp_err(struct tcp_pcb *pcb,
   void (* errf)(void *arg, err_t err))
{
  pcb->errf = errf;
}

/**
 * Used for specifying the function that should be called when a
 * LISTENing connection has been connected to another host.
 *
 */ 
void
tcp_accept(struct tcp_pcb *pcb,
     err_t (* accept)(void *arg, struct tcp_pcb *newpcb, err_t err))
{
  ((struct tcp_pcb_listen *)pcb)->accept = accept;
}
#endif /* LWIP_CALLBACK_API */


/**
 * Used to specify the function that should be called periodically
 * from TCP. The interval is specified in terms of the TCP coarse
 * timer interval, which is called twice a second.
 *
 */ 
void
tcp_poll(struct tcp_pcb *pcb,
   err_t (* poll)(void *arg, struct tcp_pcb *tpcb), u8_t interval)
{
#if LWIP_CALLBACK_API
  pcb->poll = poll;
#endif /* LWIP_CALLBACK_API */  
  pcb->pollinterval = interval;
}

/**
 * Purges a TCP PCB. Removes any buffered data and frees the buffer memory.
 *
 */
void
tcp_pcb_purge(struct tcp_pcb *pcb)
{
  if (pcb->state != CLOSED &&
     pcb->state != TIME_WAIT &&
     pcb->state != LISTEN) {

    LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge\n"));
    
    if (pcb->unsent != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: not all data sent\n"));
    }
    if (pcb->unacked != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->unacked\n"));
    }
#if TCP_QUEUE_OOSEQ /* LW */
    if (pcb->ooseq != NULL) {    
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->ooseq\n"));
    }
    
    tcp_segs_free(pcb->ooseq);
    pcb->ooseq = NULL;
#endif /* TCP_QUEUE_OOSEQ */
    tcp_segs_free(pcb->unsent);
    tcp_segs_free(pcb->unacked);
    pcb->unacked = pcb->unsent = NULL;
  }
}

/**
 * Purges the PCB and removes it from a PCB list. Any delayed ACKs are sent first.
 *
 */
void
tcp_pcb_remove(struct tcp_pcb **pcblist, struct tcp_pcb *pcb)
{
  TCP_RMV(pcblist, pcb);

  tcp_pcb_purge(pcb);
  
  /* if there is an outstanding delayed ACKs, send it */
  if (pcb->state != TIME_WAIT &&
     pcb->state != LISTEN &&
     pcb->flags & TF_ACK_DELAY) {
    pcb->flags |= TF_ACK_NOW;
    tcp_output(pcb);
  }  
  pcb->state = CLOSED;

  LWIP_ASSERT("tcp_pcb_remove: tcp_pcbs_sane()", tcp_pcbs_sane());
}

/**
 * Calculates a new initial sequence number for new connections.
 *
 */
u32_t
tcp_next_iss(void)
{
  static u32_t iss = 6510;
  
  iss += tcp_ticks;       /* XXX */
  return iss;
}

#if TCP_DEBUG || TCP_INPUT_DEBUG || TCP_OUTPUT_DEBUG
void
tcp_debug_print(struct tcp_hdr *tcphdr)
{
  LWIP_DEBUGF(TCP_DEBUG, ("TCP header:\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("|    %5u      |    %5u      | (src port, dest port)\n",
         ntohs(tcphdr->src), ntohs(tcphdr->dest)));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("|           %010lu          | (seq no)\n",
          ntohl(tcphdr->seqno)));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("|           %010lu          | (ack no)\n",
         ntohl(tcphdr->ackno)));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("| %2u |   |%u%u%u%u%u%u|     %5u     | (hdrlen, flags (",
       TCPH_HDRLEN(tcphdr),
         TCPH_FLAGS(tcphdr) >> 5 & 1,
         TCPH_FLAGS(tcphdr) >> 4 & 1,
         TCPH_FLAGS(tcphdr) >> 3 & 1,
         TCPH_FLAGS(tcphdr) >> 2 & 1,
         TCPH_FLAGS(tcphdr) >> 1 & 1,
         TCPH_FLAGS(tcphdr) & 1,
         ntohs(tcphdr->wnd)));
  tcp_debug_print_flags(TCPH_FLAGS(tcphdr));
  LWIP_DEBUGF(TCP_DEBUG, ("), win)\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
  LWIP_DEBUGF(TCP_DEBUG, ("|    0x%04x     |     %5u     | (chksum, urgp)\n",
         ntohs(tcphdr->chksum), ntohs(tcphdr->urgp)));
  LWIP_DEBUGF(TCP_DEBUG, ("+-------------------------------+\n"));
}

void
tcp_debug_print_state(enum tcp_state s)
{
  LWIP_DEBUGF(TCP_DEBUG, ("State: "));
  switch (s) {
  case CLOSED:
    LWIP_DEBUGF(TCP_DEBUG, ("CLOSED\n"));
    break;
 case LISTEN:
   LWIP_DEBUGF(TCP_DEBUG, ("LISTEN\n"));
   break;
  case SYN_SENT:
    LWIP_DEBUGF(TCP_DEBUG, ("SYN_SENT\n"));
    break;
  case SYN_RCVD:
    LWIP_DEBUGF(TCP_DEBUG, ("SYN_RCVD\n"));
    break;
  case ESTABLISHED:
    LWIP_DEBUGF(TCP_DEBUG, ("ESTABLISHED\n"));
    break;
  case FIN_WAIT_1:
    LWIP_DEBUGF(TCP_DEBUG, ("FIN_WAIT_1\n"));
    break;
  case FIN_WAIT_2:
    LWIP_DEBUGF(TCP_DEBUG, ("FIN_WAIT_2\n"));
    break;
  case CLOSE_WAIT:
    LWIP_DEBUGF(TCP_DEBUG, ("CLOSE_WAIT\n"));
    break;
  case CLOSING:
    LWIP_DEBUGF(TCP_DEBUG, ("CLOSING\n"));
    break;
  case LAST_ACK:
    LWIP_DEBUGF(TCP_DEBUG, ("LAST_ACK\n"));
    break;
  case TIME_WAIT:
    LWIP_DEBUGF(TCP_DEBUG, ("TIME_WAIT\n"));
   break;
  }
}

void
tcp_debug_print_flags(u8_t flags)
{
  if (flags & TCP_FIN) {
    LWIP_DEBUGF(TCP_DEBUG, ("FIN "));
  }
  if (flags & TCP_SYN) {
    LWIP_DEBUGF(TCP_DEBUG, ("SYN "));
  }
  if (flags & TCP_RST) {
    LWIP_DEBUGF(TCP_DEBUG, ("RST "));
  }
  if (flags & TCP_PSH) {
    LWIP_DEBUGF(TCP_DEBUG, ("PSH "));
  }
  if (flags & TCP_ACK) {
    LWIP_DEBUGF(TCP_DEBUG, ("ACK "));
  }
  if (flags & TCP_URG) {
    LWIP_DEBUGF(TCP_DEBUG, ("URG "));
  }
  if (flags & TCP_ECE) {
    LWIP_DEBUGF(TCP_DEBUG, ("ECE "));
  }
  if (flags & TCP_CWR) {
    LWIP_DEBUGF(TCP_DEBUG, ("CWR "));
  }
}

void
tcp_debug_print_pcbs(void)
{
  struct tcp_pcb *pcb;
  LWIP_DEBUGF(TCP_DEBUG, ("Active PCB states:\n"));
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    LWIP_DEBUGF(TCP_DEBUG, ("Local port %u, foreign port %u snd_nxt %lu rcv_nxt %lu ",
                       pcb->local_port, pcb->remote_port,
                       pcb->snd_nxt, pcb->rcv_nxt));
    tcp_debug_print_state(pcb->state);
  }    
  LWIP_DEBUGF(TCP_DEBUG, ("Listen PCB states:\n"));
  for(pcb = (struct tcp_pcb *)tcp_listen_pcbs.pcbs; pcb != NULL; pcb = pcb->next) {
    LWIP_DEBUGF(TCP_DEBUG, ("Local port %u, foreign port %u snd_nxt %lu rcv_nxt %lu ",
                       pcb->local_port, pcb->remote_port,
                       pcb->snd_nxt, pcb->rcv_nxt));
    tcp_debug_print_state(pcb->state);
  }    
  LWIP_DEBUGF(TCP_DEBUG, ("TIME-WAIT PCB states:\n"));
  for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
    LWIP_DEBUGF(TCP_DEBUG, ("Local port %u, foreign port %u snd_nxt %lu rcv_nxt %lu ",
                       pcb->local_port, pcb->remote_port,
                       pcb->snd_nxt, pcb->rcv_nxt));
    tcp_debug_print_state(pcb->state);
  }    
}

int
tcp_pcbs_sane(void)
{
  struct tcp_pcb *pcb;
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != CLOSED", pcb->state != CLOSED);
    LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != LISTEN", pcb->state != LISTEN);
    LWIP_ASSERT("tcp_pcbs_sane: active pcb->state != TIME-WAIT", pcb->state != TIME_WAIT);
  }
  for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {
    LWIP_ASSERT("tcp_pcbs_sane: tw pcb->state == TIME-WAIT", pcb->state == TIME_WAIT);
  }
  return 1;
}
#endif /* TCP_DEBUG */
#endif /* LWIP_TCP */