/*																www.mycal.com			
 *---------------------------------------------------------------------------
 * ahdlc.c - Ahdlc receive and transmit processor for PPP engine.
 *
 *---------------------------------------------------------------------------
 * Version  
 *		0.1 Original Version Jan 11, 1998
 *
 *--------------------------------------------------------------------------- 
 *  
 * Copyright (C) 1998, Mycal Labs www.mycal.com	
 *  
 *---------------------------------------------------------------------------
 */
/*
 * Copyright (c) 2003, Mike Johnson, Mycal Labs, www.mycal.net
 * All rights reserved. 
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met: 
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in the 
 *    documentation and/or other materials provided with the distribution. 
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Mike Johnson/Mycal Labs
 *		www.mycal.net.
 * 4. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.  
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
 *
 * This file is part of the Mycal Modified uIP TCP/IP stack.
 *
 * $Id: ahdlc.c,v 1.3 2005/01/26 23:36:22 oliverschmidt Exp $
 *
 */

/*			*/ 
/* include files 	*/
/*			*/ 
 
#include "uip.h"
#include "ppp.h"

#if 0
#define DEBUG1(x)
#else
#include <stdio.h>
#define DEBUG1(x) debug_printf x
#endif

#define	PACKET_TX_DEBUG	1

/*---------------------------------------------------------------------------
 * ahdlc flags bit defins, for ahdlc_flags variable
 ---------------------------------------------------------------------------*/
/* Escaped mode bit */
#define AHDLC_ESCAPED		0x1
/* Frame is ready bit */
#define	AHDLC_RX_READY		0x2				
#define	AHDLC_RX_ASYNC_MAP	0x4
#define AHDLC_TX_ASYNC_MAP	0x8
#define AHDLC_PFC		0x10
#define AHDLC_ACFC		0x20

/*---------------------------------------------------------------------------
 * Private Local Globals
 *	10 bytes	- standard
 *			- with counters
 ---------------------------------------------------------------------------*/
/* running tx CRC */
u16_t ahdlc_tx_crc;
/* running rx CRC */
u16_t ahdlc_rx_crc;
/* number of rx bytes processed, cur frame */
u16_t ahdlc_rx_count;
/* ahdlc state flags, see above */
u8_t ahdlc_flags;

/*
 * The following can be optimized out
 */
u8_t *ahdlc_rx_buffer;			/* What to do here? +++ */
u16_t ahdlc_max_rx_buffer_size;

/*
 * Optional statistics counters.
 */
#ifdef AHDLC_COUNTERS
u8_t ahdlc_rx_tobig_error;
#endif

/*---------------------------------------------------------------------------*/
/* Simple and fast CRC16 routine for embedded processors.
 *	Just slightly slower than the table lookup method but consumes
 *	almost no space.  Much faster and smaller than the loop and
 *	shift method that is widely used in the embedded space. 
 *	Can be optimized even more in .ASM
 *
 *	data = (crcvalue ^ inputchar) & 0xff;
 *	data = (data ^ (data << 4)) & 0xff;
 *	crc = (crc >> 8) ^ ((data << 8) ^ (data <<3) ^ (data >> 4))
 */
/*---------------------------------------------------------------------------*/
static u16_t
crcadd(u16_t crcvalue, u8_t c)
{
  u16_t b;

  b = (crcvalue ^ c) & 0xFF;
  b = (b ^ (b << 4) & 0xFF);
  b = (b << 8) ^ (b << 3) ^ (b >> 4);
  
  return ((crcvalue >> 8) ^ b);
}
/*---------------------------------------------------------------------------*/
/* ahdlc_init(buffer, buffersize) - this initializes the ahdlc engine to
 *	allow for rx frames.
 */
/*---------------------------------------------------------------------------*/
void
ahdlc_init(u8_t *buffer, u16_t maxrxbuffersize)
{
  ahdlc_flags = 0;
  ahdlc_rx_buffer = buffer;
  ahdlc_max_rx_buffer_size = maxrxbuffersize;
  /* ahdlc_async_map = 0; */
#ifdef AHDLC_COUNTERS
  ahdlc_rx_tobig_error = 0;
#endif
}
/*---------------------------------------------------------------------------*/
/* ahdlc_rx_ready() - resets the ahdlc engine to the beginning of frame 
 *	state.
 */
/*---------------------------------------------------------------------------*/
void
ahdlc_rx_ready(void)
{
  ahdlc_rx_count = 0;
  ahdlc_rx_crc = 0xffff;
  ahdlc_flags |= AHDLC_RX_READY;
}
/*---------------------------------------------------------------------------*/
/* ahdlc receive function - This routine processes incoming bytes and tries
 *	to build a PPP frame.
 *
 *	Two possible reasons that ahdlc_rx will not process characters:
 *		o Buffer is locked - in this case ahdlc_rx returns 1, char
 *			sending routing should retry.
 */
/*---------------------------------------------------------------------------*/
u8_t
ahdlc_rx(u8_t c)   
{    
  static u16_t protocol;
  
  /* check to see if PPP packet is useable, we should have hardware
     flow control set, but if host ignores it and sends us a char when
     the PPP Receive packet is in use, discard the character. +++ */
  
  if(ahdlc_flags & AHDLC_RX_READY) {
    /* check to see if character is less than 0x20 hex we really
       should set AHDLC_RX_ASYNC_MAP on by default and only turn it
       off when it is negotiated off to handle some buggy stacks. */
    if((c < 0x20) &&
       ((ahdlc_flags & AHDLC_RX_ASYNC_MAP) == 0)) {
      /* discard character */
      DEBUG1(("Discard because char is < 0x20 hex and asysnc map is 0\n"));
      return 0;
    }
    /* are we in escaped mode? */
    if(ahdlc_flags & AHDLC_ESCAPED) {
      /* set escaped to FALSE */
      ahdlc_flags &= ~AHDLC_ESCAPED;	
      
      /* if value is 0x7e then silently discard and reset receive packet */
      if(c == 0x7e) {
	ahdlc_rx_ready();
	return 0;
      }
      /* incomming char = itself xor 20 */
      c = c ^ 0x20;	
    } else if(c == 0x7e) {
      /* handle frame end */
      if(ahdlc_rx_crc == CRC_GOOD_VALUE) {
	DEBUG1(("\nReceiving packet with good crc value, len %d\n",ahdlc_rx_count));
	/* we hae a good packet, turn off CTS until we are done with
	   this packet */
	/*CTS_OFF();*/
	/* remove CRC bytes from packet */
	ahdlc_rx_count -= 2;		
	
	/* lock PPP buffer */
	ahdlc_flags &= ~AHDLC_RX_READY;
	/*
	 * upcall routine must fully process frame before return
	 *	as returning signifies that buffer belongs to AHDLC again.
	 */
	if((c & 0x1) && (ahdlc_flags & PPP_PFC)) {
	  /* Send up packet */
	  ppp_upcall((u16_t)ahdlc_rx_buffer[0],
		     (u8_t *)&ahdlc_rx_buffer[1],
		     (u16_t)(ahdlc_rx_count - 1));
	} else {
	  /* Send up packet */
	  ppp_upcall((u16_t)(ahdlc_rx_buffer[0] << 8 | ahdlc_rx_buffer[1]), 
		     (u8_t *)&ahdlc_rx_buffer[2], (u16_t)(ahdlc_rx_count - 2));
	}
	ahdlc_rx_ready();
	return 0;
      } else if(ahdlc_rx_count > 3) {	
	DEBUG1(("\nReceiving packet with bad crc value, was 0x%04x len %d\n",ahdlc_rx_crc, ahdlc_rx_count));
#ifdef AHDLC_COUNTERS
	++ahdlc_crc_error;
#endif
	/* Shouldn't we dump the packet and not pass it up? */
	/*ppp_upcall((u16_t)ahdlc_rx_buffer[0],
	  (u8_t *)&ahdlc_rx_buffer[0], (u16_t)(ahdlc_rx_count+2));
	  dump_ppp_packet(&ahdlc_rx_buffer[0],ahdlc_rx_count);*/
	
      }
      ahdlc_rx_ready();	
      return 0;
    } else if(c == 0x7d) {
      /* handle escaped chars*/
      ahdlc_flags |= PPP_ESCAPED;
      return 0;
    }
    
    /* try to store char if not to big */
    if(ahdlc_rx_count >= ahdlc_max_rx_buffer_size /*PPP_RX_BUFFER_SIZE*/) { 
#ifdef AHDLC_COUNTERS			
      ++ahdlc_rx_tobig_error;
#endif
      ahdlc_rx_ready();
    } else {
      /* Add CRC in */
      ahdlc_rx_crc = crcadd(ahdlc_rx_crc, c);
      /* do auto ACFC, if packet len is zero discard 0xff and 0x03 */
      if(ahdlc_rx_count == 0) {
	if((c == 0xff) || (c == 0x03))
	  return 0;
      }
      /* Store char */
      ppp_rx_buffer[ahdlc_rx_count++] = c;
    }		
  } else {
    /* we are busy and didn't process the character. */
    DEBUG1(("Busy/not active\n"));
    return 1;
  }
  return 0;
}
/*---------------------------------------------------------------------------*/
/* ahdlc_tx_char(char) - write a character to the serial device, 
 * escape if necessary.
 *
 * Relies on local global vars	:	ahdlc_tx_crc, ahdlc_flags.
 * Modifies local global vars	:	ahdlc_tx_crc.
 */
/*---------------------------------------------------------------------------*/
void
ahdlc_tx_char(u16_t protocol, u8_t c)
{
  /* add in crc */
  ahdlc_tx_crc = crcadd(ahdlc_tx_crc, c);
  /*
   * See if we need to escape char, we always escape 0x7d and 0x7e, in the case
   * of char < 0x20 we only support async map of default or none, so escape if
   * ASYNC map is not set.  We may want to modify this to support a bitmap set
   * ASYNC map.
   */
  if((c == 0x7d) || (c == 0x7e) || 
     ((c < 0x20) && ((protocol == LCP) ||
		     (ahdlc_flags & PPP_TX_ASYNC_MAP) == 0))) {
    /* send escape char and xor byte by 0x20 */
    ppp_arch_putchar(0x7d);
    c ^= 0x20;
  }
  ppp_arch_putchar(c);
}
/*---------------------------------------------------------------------------*/
/* ahdlc_tx(protocol,buffer,len) - Transmit a PPP frame.
 *	Buffer contains protocol data, ahdlc_tx addes address, control and
 *	protocol data.
 *
 * Relies on local global vars	:	ahdlc_tx_crc, ahdlc_flags.
 * Modifies local global vars	:	ahdlc_tx_crc.
 */
/*---------------------------------------------------------------------------*/
u8_t
ahdlc_tx(u16_t protocol, u8_t *header, u8_t *buffer,
	 u16_t headerlen, u16_t datalen)
{
  u16_t i;
  u8_t c;

  DEBUG1(("\nAHDLC_TX - transmit frame, protocol 0x%04x, length %d\n",protocol,datalen+headerlen));
  
#if PACKET_TX_DEBUG
  DEBUG1(("\n"));
  for(i = 0; i < headerlen; ++i) {
    DEBUG1(("0x%02x ", header[i]));
  }
  for(i = 0; i < datalen; ++i) {
    DEBUG1(("0x%02x ", buffer[i]));
  }
  DEBUG1(("\n\n"));
#endif

  /* Check to see that physical layer is up, we can assume is some
     cases */
  
  /* write leading 0x7e */
  ppp_arch_putchar(0x7e);

  /* set initial CRC value */
  ahdlc_tx_crc = 0xffff;
  /* send HDLC control and address if not disabled or of LCP frame type */
  /*if((0==(ahdlc_flags & PPP_ACFC)) || ((0xc0==buffer[0]) && (0x21==buffer[1]))) */
  if((0 == (ahdlc_flags & PPP_ACFC)) || (protocol == LCP)) {
    ahdlc_tx_char(protocol, 0xff);
    ahdlc_tx_char(protocol, 0x03);
  }
  
  /* Write Protocol */
  ahdlc_tx_char(protocol,(u8_t)(protocol >> 8));
  ahdlc_tx_char(protocol,(u8_t)(protocol & 0xff));

  /* write header if it exists */
  for(i = 0; i < headerlen; ++i) {
    /* Get next byte from buffer */
    c = header[i];
    /* Write it...*/
    ahdlc_tx_char(protocol, c);
  }

  /* Write frame bytes */
  for(i = 0; i < datalen; ++i) {    
    /* Get next byte from buffer */
    c = buffer[i];
    /* Write it...*/
    ahdlc_tx_char(protocol, c);
  }
	
  /* send crc, lsb then msb */
  i = ahdlc_tx_crc ^ 0xffff;
  ahdlc_tx_char(protocol, (u8_t)(i & 0xff));
  ahdlc_tx_char(protocol, (u8_t)((i >> 8) & 0xff));

  /* write trailing 0x7e, probably not needed but it doesn't hurt*/
  ppp_arch_putchar(0x7e);
  return 0;
}
/*---------------------------------------------------------------------------*/