source: rtems/cpukit/libnetworking/net/ppp_tty.c @ 1c6926c1

/*
 * ppp_tty.c - Point-to-Point Protocol (PPP) driver for asynchronous
 *             tty devices.
 *
 * Copyright (c) 1989 Carnegie Mellon University.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by Carnegie Mellon University.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Drew D. Perkins
 * Carnegie Mellon University
 * 4910 Forbes Ave.
 * Pittsburgh, PA 15213
 * (412) 268-8576
 * ddp@andrew.cmu.edu
 *
 * Based on:
 *      @(#)if_sl.c     7.6.1.2 (Berkeley) 2/15/89
 *
 * Copyright (c) 1987 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Serial Line interface
 *
 * Rick Adams
 * Center for Seismic Studies
 * 1300 N 17th Street, Suite 1450
 * Arlington, Virginia 22209
 * (703)276-7900
 * rick@seismo.ARPA
 * seismo!rick
 *
 * Pounded on heavily by Chris Torek (chris@mimsy.umd.edu, umcp-cs!chris).
 * Converted to 4.3BSD Beta by Chris Torek.
 * Other changes made at Berkeley, based in part on code by Kirk Smith.
 *
 * Converted to 4.3BSD+ 386BSD by Brad Parker (brad@cayman.com)
 * Added VJ tcp header compression; more unified ioctls
 *
 * Extensively modified by Paul Mackerras (paulus@cs.anu.edu.au).
 * Cleaned up a lot of the mbuf-related code to fix bugs that
 * caused system crashes and packet corruption.  Changed pppstart
 * so that it doesn't just give up with a "collision" if the whole
 * packet doesn't fit in the output ring buffer.
 *
 * Added priority queueing for interactive IP packets, following
 * the model of if_sl.c, plus hooks for bpf.
 * Paul Mackerras (paulus@cs.anu.edu.au).
 */

/* $FreeBSD: src/sys/net/ppp_tty.c,v 1.69 2005/10/16 20:44:18 phk Exp $ */
/* from if_sl.c,v 1.11 84/10/04 12:54:47 rick Exp */
/* from NetBSD: if_ppp.c,v 1.15.2.2 1994/07/28 05:17:58 cgd Exp */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "opt_ppp.h"            /* XXX for ppp_defs.h */

#if NPPP > 0

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/file.h>
#include <sys/kernel.h>

#include <net/if.h>
#include <net/if_types.h>

#ifdef VJC
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <net/slcompress.h>
#endif

#include <rtems.h>
#include <rtems/libio.h>
#include <sys/ttycom.h>
#include <termios.h>
#include <rtems/termiostypes.h>

#ifdef PPP_FILTER
#include <net/bpf.h>
#endif
#include <net/ppp_defs.h>
#include <net/if_ppp.h>
#include <net/if_pppvar.h>


void    pppasyncattach(void);
int     pppopen(struct rtems_termios_tty *tty);
int     pppclose(struct rtems_termios_tty *tty);
int     pppread(struct rtems_termios_tty *tty, rtems_libio_rw_args_t *rw_args);
int     pppwrite(struct rtems_termios_tty *tty, rtems_libio_rw_args_t *rw_args);
int     ppptioctl(struct rtems_termios_tty *tty, rtems_libio_ioctl_args_t *args);
int     pppinput(int c, struct rtems_termios_tty *tty);
int     pppstart(struct rtems_termios_tty *tp);
u_short pppfcs(u_short fcs, u_char *cp, int len);
void    pppallocmbuf(struct ppp_softc *sc, struct mbuf **mp);

static void pppasyncstart(struct ppp_softc *);
static void pppasyncctlp(struct ppp_softc *);
static void pppasyncrelinq(struct ppp_softc *);
/*static void ppp_timeout __P((void *)); */
/*static void pppdumpb __P((u_char *b, int l)); */
/*static void ppplogchar __P((struct ppp_softc *, int)); */

/*
 * Some useful mbuf macros not in mbuf.h.
 */
#define M_IS_CLUSTER(m) ((m)->m_flags & M_EXT)

#define M_DATASTART(m)  \
        (M_IS_CLUSTER(m) ? (m)->m_ext.ext_buf : \
            (m)->m_flags & M_PKTHDR ? (m)->m_pktdat : (m)->m_dat)

#define M_DATASIZE(m)   \
        (M_IS_CLUSTER(m) ? (m)->m_ext.ext_size : \
            (m)->m_flags & M_PKTHDR ? MHLEN: MLEN)

/*
 * We steal two bits in the mbuf m_flags, to mark high-priority packets
 * for output, and received packets following lost/corrupted packets.
 */
#define M_HIGHPRI       0x2000  /* output packet for sc_fastq */
#define M_ERRMARK       0x4000  /* steal a bit in mbuf m_flags */

/*
 * Does c need to be escaped?
 */
#define ESCAPE_P(c)     (sc->sc_asyncmap[(c) >> 5] & (1 << ((c) & 0x1F)))

/*
 * Procedures for using an async tty interface for PPP.
 */

/* This is a FreeBSD-2.0 kernel. */
#define CCOUNT(rb)      (((rb).Size+(rb).Head-(rb).Tail) % (rb).Size)
#define FCOUNT(rb)      ((rb).Size-CCOUNT(rb)-1)
#define PPP_LOWAT       100     /* Process more output when < LOWAT on queue */
#define PPP_HIWAT       400     /* Don't start a new packet if HIWAT on que */

/*
 * Define the PPP line discipline.
 */

static struct rtems_termios_linesw pppdisc = {
        pppopen, pppclose, pppread, pppwrite,
        pppinput, pppstart, ppptioctl, NULL
};

void
pppasyncattach(void)
{
    rtems_termios_linesw[PPPDISC] = pppdisc;
}

TEXT_SET(pseudo_set, pppasyncattach);

/*
 * Line specific open routine for async tty devices.
 * Attach the given tty to the first available ppp unit.
 * Called from device open routine or ttioctl.
 */
/* ARGSUSED */
int
pppopen(struct rtems_termios_tty *tty)
{
    int                        i;
    register struct ppp_softc *sc;
    struct mbuf *m = (struct mbuf *)0;

    if (tty->t_line == PPPDISC) {
        sc = (struct ppp_softc *)tty->t_sc;
        if (sc != NULL && sc->sc_devp == (void *)tty) {
            return (0);
        }
    }

    if ((sc = pppalloc(1)) == NULL) {
        return ENXIO;
    }

    if (sc->sc_relinq)
        (*sc->sc_relinq)(sc);   /* get previous owner to relinquish the unit */

    sc->sc_ilen = 0;
    sc->sc_m = NULL;
    bzero(sc->sc_asyncmap, sizeof(sc->sc_asyncmap));
    sc->sc_asyncmap[0] = 0xffffffff;
    sc->sc_asyncmap[3] = 0x60000000;
    sc->sc_rasyncmap = 0;
    sc->sc_devp = tty;
    sc->sc_start = pppasyncstart;
    sc->sc_ctlp = pppasyncctlp;
    sc->sc_relinq = pppasyncrelinq;
    sc->sc_outm = NULL;
    sc->sc_outmc = NULL;

    /* preallocate mbufs for free queue */
    rtems_bsdnet_semaphore_obtain();
    for (i=0; i<NUM_MBUFQ; i++) {
      pppallocmbuf(sc, &m);
      if ( i == 0 ) {
        /* use first mbuf for rx iterrupt handling */
        sc->sc_m = m;
      }
      else {
        /* enqueue mbuf for later use */
        IF_ENQUEUE(&sc->sc_freeq, m);
      }
      m = (struct mbuf *)0;
    }
    rtems_bsdnet_semaphore_release();

    /* initialize values */
    sc->sc_if.if_flags |= IFF_RUNNING;
    sc->sc_if.if_baudrate = tty->termios.c_ispeed;

    tty->t_sc = (void *)sc;

    return ( RTEMS_SUCCESSFUL );
}

/*
 * Line specific close routine, called from device close routine
 * and from ttioctl.
 * Detach the tty from the ppp unit.
 * Mimics part of ttyclose().
 */
int
pppclose(struct rtems_termios_tty *tty)
{
    register struct ppp_softc *sc;

    tty->t_line = 0;
    sc = (struct ppp_softc *)tty->t_sc;
    if (sc != NULL) {
        tty->t_sc = NULL;
        if (tty == (struct rtems_termios_tty *)sc->sc_devp) {
            rtems_bsdnet_semaphore_obtain();
            pppasyncrelinq(sc);
            pppdealloc(sc);
            rtems_bsdnet_semaphore_release();
        }
    }
    return ( RTEMS_SUCCESSFUL );
}

/*
 * Relinquish the interface unit to another device.
 */
static void
pppasyncrelinq(struct ppp_softc *sc)
{
#ifdef XXX_XXX
    if (sc->sc_outm) {
        m_freem(sc->sc_outm);
        sc->sc_outm = NULL;
    }
    if (sc->sc_m) {
        m_freem(sc->sc_m);
        sc->sc_m = NULL;
    }
    if (sc->sc_flags & SC_TIMEOUT) {
        untimeout(ppp_timeout, (void *) sc);
        sc->sc_flags &= ~SC_TIMEOUT;
    }
#endif
}

/*
 * Line specific (tty) read routine.
 */
int
pppread(struct rtems_termios_tty *tty, rtems_libio_rw_args_t *rw_args)
{
    rtems_status_code            status  = RTEMS_UNSATISFIED;
    int                          count   = 0;
    int                          maximum = rw_args->count;
    char                        *buffer  = rw_args->buffer;
    register struct ppp_softc   *sc      = (struct ppp_softc *)tty->t_sc;
    struct mbuf                 *m;
    struct mbuf                 *m0;
    u_char                      *p;

    if (sc == NULL)
        return 0;

    /*
     * Loop waiting for input, checking that nothing disasterous
     * happens in the meantime.
     */
    if (tty != (struct rtems_termios_tty *)sc->sc_devp || tty->t_line != PPPDISC) {
        return ( status );
    }
    if (sc->sc_inq.ifq_head == NULL) {
      return ( status );
    }

    /* Get the packet from the input queue */
    rtems_bsdnet_semaphore_obtain();
    IF_DEQUEUE(&sc->sc_inq, m0);

    /* loop over mbuf chain */
    m = m0;
    while (( m != NULL ) && ( m->m_len > 0 ) && ( count+m->m_len < maximum )) {
      /* copy data into buffer */
      p = mtod(m, u_char *);
      memcpy(buffer, p, m->m_len);
      memset(p, 0, m->m_len);
      count  += m->m_len;
      buffer += m->m_len;

      /* increment loop index */
      m = m->m_next;
    }

    /* free mbuf chain */
    m_freem(m0);
    rtems_bsdnet_semaphore_release();

    /* update return values */
    rw_args->bytes_moved = count;
    if ( count >= 0 ) {
      status = RTEMS_SUCCESSFUL;
    }

    /* check to see if queue is empty */
    if (sc->sc_inq.ifq_head != NULL) {
      /* queue is not empty - post another event to ourself */
      rtems_event_send(sc->sc_pppdtask, PPPD_EVENT);
    }

    return ( status );
}

/*
 * Line specific (tty) write routine.
 */
int
pppwrite(struct rtems_termios_tty *tty, rtems_libio_rw_args_t *rw_args)
{
    struct sockaddr               dst;
    int                           n;
    int                           len;
    int                           maximum    = rw_args->count;
    char                         *out_buffer = rw_args->buffer;
    register struct ppp_softc    *sc         = (struct ppp_softc *)tty->t_sc;
    struct mbuf                  *m;
    struct mbuf                  *m0;
    struct mbuf                 **mp;

    rtems_bsdnet_semaphore_obtain();
    for (mp = &m0; maximum; mp = &m->m_next) {
        MGET(m, M_WAIT, MT_DATA);
        if ((*mp = m) == NULL) {
            m_freem(m0);
            return (ENOBUFS);
        }
        m->m_len = 0;
        if (maximum >= MCLBYTES / 2) {
            MCLGET(m, M_DONTWAIT);
        }
        len = M_TRAILINGSPACE(m);
        if (len > maximum) {
          memcpy(mtod(m, u_char *),out_buffer,maximum);
          m->m_len = maximum;
          maximum  = 0;
        }
        else {
          memcpy(mtod(m, u_char *),out_buffer,len);
          m->m_len    = len;
          maximum    -= len;
          out_buffer += len;
        }
    }

    dst.sa_family = AF_UNSPEC;
    bcopy(mtod(m0, u_char *), dst.sa_data, PPP_HDRLEN);
    m0->m_data += PPP_HDRLEN;
    m0->m_len  -= PPP_HDRLEN;

    n = pppoutput(&sc->sc_if, m0, &dst, (struct rtentry *)0);
    rtems_bsdnet_semaphore_release();

    return ( n );
}

/*
 * Line specific (tty) ioctl routine.
 * This discipline requires that tty device drivers call
 * the line specific l_ioctl routine from their ioctl routines.
 */
/* ARGSUSED */
int
ppptioctl(struct rtems_termios_tty *tty, rtems_libio_ioctl_args_t *args)
{
/*    int                 i;    */
    int                 error = RTEMS_SUCCESSFUL;
    ioctl_command_t     cmd   = args->command;
    caddr_t             data  = args->buffer;
    struct ppp_softc   *sc    = tty->t_sc;

    switch (cmd) {
    case TIOCGETA:
    case TIOCSETA:
    case TIOCSETAW:
    case TIOCSETAF:
    case TIOCDRAIN:
    case RTEMS_IO_SNDWAKEUP:
    case RTEMS_IO_RCVWAKEUP:
    case TIOCGETD:
    case TIOCSETD:
        error = rtems_termios_ioctl(args);
        break;

    case PPPIOCSASYNCMAP:
        sc->sc_asyncmap[0] = *(u_int *)data;
        break;

    case PPPIOCGASYNCMAP:
        *(u_int *)data = sc->sc_asyncmap[0];
        break;

    case PPPIOCSRASYNCMAP:
        sc->sc_rasyncmap = *(u_int *)data;
        break;

    case PPPIOCGRASYNCMAP:
        *(u_int *)data = sc->sc_rasyncmap;
        break;

    case PPPIOCSXASYNCMAP:
        bcopy(data, sc->sc_asyncmap, sizeof(sc->sc_asyncmap));
        sc->sc_asyncmap[1] = 0;             /* mustn't escape 0x20 - 0x3f */
        sc->sc_asyncmap[2] &= ~0x40000000;  /* mustn't escape 0x5e */
        sc->sc_asyncmap[3] |= 0x60000000;   /* must escape 0x7d, 0x7e */
        break;

    case PPPIOCGXASYNCMAP:
        bcopy(sc->sc_asyncmap, data, sizeof(sc->sc_asyncmap));
        break;

    default:
        rtems_bsdnet_semaphore_obtain();
        error = pppioctl(sc, cmd, data, 0, NULL);
        rtems_bsdnet_semaphore_release();
    }
    return error;
}

/*
 * FCS lookup table as calculated by genfcstab.
 */
static u_short fcstab[256] = {
        0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
        0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
        0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
        0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
        0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
        0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
        0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
        0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
        0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
        0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
        0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
        0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
        0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
        0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
        0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
        0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
        0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
        0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
        0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
        0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
        0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
        0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
        0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
        0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
        0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
        0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
        0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
        0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
        0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
        0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
        0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
        0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

/*
 * Calculate a new FCS given the current FCS and the new data.
 */
u_short
pppfcs(u_short fcs, u_char *cp, int len)
{
    while (len--)
        fcs = PPP_FCS(fcs, *cp++);
    return (fcs);
}

/*
 * This gets called at splsoftnet from if_ppp.c at various times
 * when there is data ready to be sent.
 */
void pppasyncstart(struct ppp_softc *sc)
{
  /* check to see if output is not active */
  if ( sc->sc_outflag == 0 ) {
    /* mark active and post tx event to daemon */
    sc->sc_outflag |= SC_TX_PENDING;
    rtems_event_send(sc->sc_txtask, TX_PACKET);
  }
}

/*
 * This gets called when a received packet is placed on
 * the inq, at splsoftnet.
 */
static void
pppasyncctlp(
    struct ppp_softc *sc)
{
  /* check to see if task id was set */
  if ( sc->sc_pppdtask != 0 ) {
    /* post event to daemon */
    rtems_event_send(sc->sc_pppdtask, PPPD_EVENT);
  }
}

/*
 * Start output on async tty interface.  If the transmit queue
 * has drained sufficiently, arrange for pppasyncstart to be
 * called later at splsoftnet.
 * Called at spltty or higher.
 */
int
pppstart(struct rtems_termios_tty *tp)
{
  u_char             *sendBegin;
  u_long              ioffset = (u_long       )0;
  struct mbuf        *m       = (struct mbuf *)0;
  struct ppp_softc   *sc      = tp->t_sc;
  rtems_termios_device_context *ctx = rtems_termios_get_device_context(tp);

  /* ensure input is valid and we are busy */
  if (( sc != NULL ) && ( sc->sc_outflag & SC_TX_BUSY )) {
    /* check to see if we need to get the next buffer */

    /* Ready with PPP_FLAG Character ? */
    if(sc->sc_outflag & SC_TX_LASTCHAR){
        sc->sc_outflag &= ~(SC_TX_BUSY | SC_TX_FCS | SC_TX_LASTCHAR);

        /* Notify driver that we have nothing to transmit */
        (*tp->handler.write)(ctx, NULL, 0);

        rtems_event_send(sc->sc_txtask, TX_TRANSMIT);   /* Ready for the next Packet */
        return(0);
    }

    if ( sc->sc_outoff >= sc->sc_outlen ) {
      /* loop to get next non-zero length buffer */
      if ( sc->sc_outmc != NULL ) {
        m = sc->sc_outmc->m_next;
      }

      /* check for next mbuf in chain */
      if ( m != NULL ) {
        /* update values to use this mbuf */
        sc->sc_outmc  = m;
        sc->sc_outbuf = mtod(m, u_char *);
        sc->sc_outlen = m->m_len;
        sc->sc_outoff = (short)0;
      }
      else if ( (sc->sc_outflag & SC_TX_FCS) == 0 ) {
        /* setup to use FCS buffer */
        sc->sc_outflag |= SC_TX_FCS;
        sc->sc_outbuf   = sc->sc_outfcsbuf;
        sc->sc_outlen   = sc->sc_outfcslen;
        sc->sc_outoff   = (short)0;
      }
      else {
        /* done with this packet */
        sc->sc_outflag |= SC_TX_LASTCHAR;
        sc->sc_outflag &=~(SC_TX_FCS);
                sc->sc_outchar = (u_char)PPP_FLAG;
        (*tp->handler.write)(ctx, (char *)&sc->sc_outchar, 1);
        return(0);
      }
    }

    /* check to see if there is some data to write out */
    if ( sc->sc_outoff < sc->sc_outlen ) {
      /* check to see if character needs to be escaped */
      sc->sc_outchar = sc->sc_outbuf[sc->sc_outoff];
      if ( ESCAPE_P(sc->sc_outchar) ) {
        if ( sc->sc_outflag & SC_TX_ESCAPE ) {
          /* last sent character was the escape character */
          sc->sc_outchar = sc->sc_outchar ^ PPP_TRANS;

          /* clear the escape flag and increment the offset */
          sc->sc_outflag &= ~SC_TX_ESCAPE;
          ioffset++;
        }
        else {
          /* need to send the escape character */
          sc->sc_outchar = PPP_ESCAPE;

          /* set the escape flag */
          sc->sc_outflag |= SC_TX_ESCAPE;
        }
        sendBegin = &sc->sc_outchar;
      }
      else {
        /* escape not needed - increment the offset as much as possible */
        while ((!ESCAPE_P(sc->sc_outchar)) && ((sc->sc_outoff + ioffset) < sc->sc_outlen)) {
            ioffset++;
            sc->sc_outchar = sc->sc_outbuf[sc->sc_outoff + ioffset];
        }
        sendBegin = &sc->sc_outbuf[sc->sc_outoff];
      }

      /* write out the character(s) and update the stats */
      (*tp->handler.write)(ctx, (char *)sendBegin, (ioffset > 0) ? ioffset : 1);
      sc->sc_stats.ppp_obytes += (ioffset > 0) ? ioffset : 1;
      sc->sc_outoff += ioffset;

      return (0);
    }
  }

  /* Notify driver that we have nothing to transmit */
  (*tp->handler.write)(ctx, NULL, 0);

  return (0);
}

#ifdef XXX_XXX
/*
 * Timeout routine - try to start some more output.
 */
static void
ppp_timeout(void *x)
{
    struct rtems_termios_tty *tty = (struct rtems_termios_tty *)x;
    struct ppp_softc         *sc  = tty->t_sc;
/*    struct rtems_termios_tty *tp  = (struct rtems_termios_tty *)sc->sc_devp; */

    sc->sc_flags &= ~SC_TIMEOUT;
/*    pppstart(tp); */
}
#endif

/*
 * Allocate enough mbuf to handle current MRU.
 */
#ifdef XXX_XXX
static void
pppgetm(struct ppp_softc *sc)
{
    struct mbuf *m, **mp;
    int len;

    mp = &sc->sc_m;
    for (len = sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN; len > 0; ){
        if ((m = *mp) == NULL) {
            MGETHDR(m, M_DONTWAIT, MT_DATA);
            if (m == NULL)
                break;
            *mp = m;
            MCLGET(m, M_DONTWAIT);
        }
        len -= M_DATASIZE(m);
        mp = &m->m_next;
    }
}
#endif

void
pppallocmbuf(struct ppp_softc *sc, struct mbuf **mp)
{
  int            ilen;
  struct mbuf   *m;

  /* loop over length value */
  ilen = sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN;
  while ( ilen > 0 ) {
    /* see if this is end of the chain */
    m = *mp;
    if ( m == NULL ) {
      /* get mbuf header */
      MGETHDR(m, M_WAIT, MT_DATA);
      MCLGET(m, M_WAIT);
      *mp = m;
    }

    /* update loop variables */
    mp    = &m->m_next;
    ilen -= M_DATASIZE(m);
  }
}

/*
 * tty interface receiver interrupt.
 */
static uint32_t paritytab[8] = {
    0x96696996L, 0x69969669L, 0x69969669L, 0x96696996L,
    0x69969669L, 0x96696996L, 0x96696996L, 0x69969669L
};

int
pppinput(int c, struct rtems_termios_tty *tp)
{
    register struct ppp_softc *sc = tp->t_sc;
    struct mbuf *m;
    int ilen;

    if (sc == NULL || tp != (struct rtems_termios_tty *)sc->sc_devp)
        return 0;
    if (sc->sc_m == NULL) {
        rtems_event_send(sc->sc_rxtask, RX_EMPTY);
        IF_DEQUEUE(&sc->sc_freeq, sc->sc_m);
        if ( sc->sc_m == NULL ) {
          return 0;
        }
    }

    ++sc->sc_stats.ppp_ibytes;

    c &= 0xff;
    if (c & 0x80)
        sc->sc_flags |= SC_RCV_B7_1;
    else
        sc->sc_flags |= SC_RCV_B7_0;
    if (paritytab[c >> 5] & (1 << (c & 0x1F)))
        sc->sc_flags |= SC_RCV_ODDP;
    else
        sc->sc_flags |= SC_RCV_EVNP;

    if (c == PPP_FLAG) {
        ilen = sc->sc_ilen;
        sc->sc_ilen = 0;

        /*
         * If SC_ESCAPED is set, then we've seen the packet
         * abort sequence "}~".
         */
        if (sc->sc_flags & (SC_FLUSH | SC_ESCAPED)
            || (ilen > 0 && sc->sc_fcs != PPP_GOODFCS)) {
            sc->sc_flags |= SC_PKTLOST; /* note the dropped packet */
            if ((sc->sc_flags & (SC_FLUSH | SC_ESCAPED)) == 0){
                /* bad fcs error */
                sc->sc_if.if_ierrors++;
                sc->sc_stats.ppp_ierrors++;
            } else
                sc->sc_flags &= ~(SC_FLUSH | SC_ESCAPED);
            return 0;
        }

        if (ilen < PPP_HDRLEN + PPP_FCSLEN) {
            if (ilen) {
                /* too short error */
                sc->sc_if.if_ierrors++;
                sc->sc_stats.ppp_ierrors++;
                sc->sc_flags |= SC_PKTLOST;
            }
            return 0;
        }

        /* Remove FCS trailer.  Somewhat painful... */
        ilen -= 2;
        if (--sc->sc_mc->m_len == 0) {
            for (m = sc->sc_m; m->m_next != sc->sc_mc; m = m->m_next);
            sc->sc_mc = m;
        }
        sc->sc_mc->m_len--;

        /* excise this mbuf chain - place on raw queue */
        m = sc->sc_m;
        if ( sc->sc_flags & SC_PKTLOST ) {
          m->m_flags   |= M_ERRMARK;
          sc->sc_flags &= ~SC_PKTLOST;
        }
        IF_ENQUEUE(&sc->sc_rawq, m);

        /* setup next mbuf chain */
        IF_DEQUEUE(&sc->sc_freeq, sc->sc_m);

        /* send rx packet event */
        rtems_event_send(sc->sc_rxtask, RX_PACKET);
        return 0;
    }

    if (c < 0x20 && (sc->sc_rasyncmap & (1 << c)))
        return 0;

    if (sc->sc_flags & SC_ESCAPED) {
        sc->sc_flags &= ~SC_ESCAPED;
        c ^= PPP_TRANS;
    } else if (c == PPP_ESCAPE) {
        sc->sc_flags |= SC_ESCAPED;
        return 0;
    }

    /*
     * Initialize buffer on first octet received.
     * First octet could be address or protocol (when compressing
     * address/control).
     * Second octet is control.
     * Third octet is first or second (when compressing protocol)
     * octet of protocol.
     * Fourth octet is second octet of protocol.
     */
    if (sc->sc_ilen == 0) {
        m = sc->sc_m;
        m->m_len = 0;
        m->m_data = M_DATASTART(sc->sc_m);
        sc->sc_mc = m;
        sc->sc_mp = mtod(m, char *);
        sc->sc_fcs = PPP_INITFCS;
        if (c != PPP_ALLSTATIONS) {
            if (sc->sc_flags & SC_REJ_COMP_AC) {
                /* garbage received error */
                goto flush;
            }
            *sc->sc_mp++ = PPP_ALLSTATIONS;
            *sc->sc_mp++ = PPP_UI;
            sc->sc_ilen += 2;
            m->m_len += 2;
        }
    }
    if (sc->sc_ilen == 1 && c != PPP_UI) {
        /* missing UI error */
        goto flush;
    }
    if (sc->sc_ilen == 2 && (c & 1) == 1) {
        /* a compressed protocol */
        *sc->sc_mp++ = 0;
        sc->sc_ilen++;
        sc->sc_mc->m_len++;
    }
    if (sc->sc_ilen == 3 && (c & 1) == 0) {
        /* bad protocol error */
        goto flush;
    }

    /* packet beyond configured mru? */
    if (++sc->sc_ilen > sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN) {
        /* packet too big error */
        goto flush;
    }

    /* is this mbuf full? */
    m = sc->sc_mc;
    if (M_TRAILINGSPACE(m) <= 0) {
        if (m->m_next == NULL) {
          /* get next available mbuf for the chain */
          IF_DEQUEUE(&sc->sc_freeq, m->m_next);
          if (m->m_next == NULL) {
            /* too few mbufs */
            goto flush;
          }
          else {
            /* send rx mbuf event */
            rtems_event_send(sc->sc_rxtask, RX_MBUF);
          }
        }
        sc->sc_mc = m = m->m_next;
        m->m_len  = 0;
        m->m_next = 0;
        m->m_data = M_DATASTART(m);
        sc->sc_mp = mtod(m, char *);
    }

    ++m->m_len;
    *sc->sc_mp++ = c;
    sc->sc_fcs = PPP_FCS(sc->sc_fcs, c);
    return 0;

 flush:
    if (!(sc->sc_flags & SC_FLUSH)) {
        sc->sc_if.if_ierrors++;
        sc->sc_stats.ppp_ierrors++;
        sc->sc_flags |= SC_FLUSH;
    }
    return 0;
}

#ifdef XXX_XXX
#define MAX_DUMP_BYTES  128

static void
ppplogchar(struct ppp_softc *sc, int c)
{
    if (c >= 0)
        sc->sc_rawin[sc->sc_rawin_count++] = c;
    if (sc->sc_rawin_count >= sizeof(sc->sc_rawin)
        || (c < 0 && sc->sc_rawin_count > 0)) {
        printf("ppp%d input: ", sc->sc_if.if_unit);
        pppdumpb(sc->sc_rawin, sc->sc_rawin_count);
        sc->sc_rawin_count = 0;
    }
}

static void
pppdumpb(u_char *b, int l)
{
    char buf[3*MAX_DUMP_BYTES+4];
    char *bp = buf;
    static char digits[] = "0123456789abcdef";

    while (l--) {
        if (bp >= buf + sizeof(buf) - 3) {
            *bp++ = '>';
            break;
        }
        *bp++ = digits[*b >> 4]; /* convert byte to ascii hex */
        *bp++ = digits[*b++ & 0xf];
        *bp++ = ' ';
    }

    *bp = 0;
    printf("%s\n", buf);
}
#endif

#endif  /* NPPP > 0 */