serval-dna/mavlink.c

// -*- Mode: C; c-basic-offset: 2; -*-
//
// Copyright (c) 2012 Andrew Tridgell, All Rights Reserved
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
//
//  o Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
//  o 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.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "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
// COPYRIGHT HOLDER OR CONTRIBUTORS 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,
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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/*
Portions Copyright (C) 2013 Paul Gardner-Stephen
 
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
 
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

#include "serval.h"
#include "conf.h"
#include "overlay_buffer.h"

#define MAVLINK_MSG_ID_RADIO 166
#define MAVLINK_MSG_ID_DATASTREAM 67
int MAVLINK_MESSAGE_CRCS[]={72, 39, 190, 92, 191, 217, 104, 119, 0, 219, 60, 186, 10, 0, 0, 0, 0, 0, 0, 0, 89, 159, 162, 121, 0, 149, 222, 110, 179, 136, 66, 126, 185, 147, 112, 252, 162, 215, 229, 128, 9, 106, 101, 213, 4, 229, 21, 214, 215, 14, 206, 50, 157, 126, 108, 213, 95, 5, 127, 0, 0, 0, 57, 126, 130, 119, 193, 191, 236, 158, 143, 0, 0, 104, 123, 131, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 174, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 155, 0, 0, 0, 0, 0, 0, 0, 0, 0, 143, 29, 208, 188, 118, 242, 19, 97, 233, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 178, 224, 60, 106, 7};

// use '3D' for 3DRadio
#define RADIO_SOURCE_SYSTEM '3'
#define RADIO_SOURCE_COMPONENT 'D'

uint16_t mavlink_crc(unsigned char *buf,int length)
{
  uint16_t sum = 0xFFFF;
  uint8_t i, stoplen;
  
  stoplen = length + 6;
  
  // MAVLink 1.0 has an extra CRC seed
  buf[length+6] = MAVLINK_MESSAGE_CRCS[buf[5]];
  stoplen++;
  
  i = 1;
  while (i<stoplen) {
    uint8_t tmp;
    tmp = buf[i] ^ (uint8_t)(sum&0xff);
    tmp ^= (tmp<<4);
    sum = (sum>>8) ^ (tmp<<8) ^ (tmp<<3) ^ (tmp>>4);
    i++;
  }
  buf[length+6]=sum&0xff;
  buf[length+7]=sum>>8;
  
  return sum;
}


/*
  we use a hand-crafted MAVLink packet based on the following
  message definition
  
  <message name="RADIO" id="166">
  <description>Status generated by radio</description>
  <field type="uint8_t" name="rssi">local signal strength</field>
  <field type="uint8_t" name="remrssi">remote signal strength</field>
  <field type="uint8_t" name="txbuf">percentage free space in transmit buffer</field>
  <field type="uint8_t" name="noise">background noise level</field>
  <field type="uint8_t" name="remnoise">remote background noise level</field>
  <field type="uint16_t" name="rxerrors">receive errors</field>
  <field type="uint16_t" name="fixed">count of error corrected packets</field>
  </message>
*/
struct mavlink_RADIO_v09 {
  uint8_t rssi;
  uint8_t remrssi;
  uint8_t txbuf;
  uint8_t noise;
  uint8_t remnoise;
  uint16_t rxerrors;
  uint16_t fixed;
};
struct mavlink_RADIO_v10 {
  uint16_t rxerrors;
  uint16_t fixed;
  uint8_t rssi;
  uint8_t remrssi;
  uint8_t txbuf;
  uint8_t noise;
  uint8_t remnoise;
};

/*
  Each mavlink frame consists of 0xfe followed by a standard 6 byte header.
  Normally the payload plus a 2-byte CRC follows.
  We are replacing the CRC check with a Reed-Solomon code to correct as well
  as detect upto 16 bytes with errors, in return for a 32-byte overhead.

  The nature of the particular library we are using is that the overhead is
  basically fixed, but we can shorten the data section.  

  Note that the mavlink headers are not protected against errors.  This is a
  limitation of the radio firmware at present. One day we will re-write the
  radio firmware so that we can send and receive raw radio frames, and get
  rid of the mavlink framing altogether, and just send R-S protected payloads.

  Not ideal, but will be fine for now.
*/

#include "fec-3.0.1/fixed.h"
void encode_rs_8(data_t *data, data_t *parity,int pad);
int decode_rs_8(data_t *data, int *eras_pos, int no_eras, int pad);

int mavlink_encode_packet(struct overlay_interface *interface)
{
  int count = ob_remaining(interface->tx_packet);
  int startP = !ob_position(interface->tx_packet);
  int endP = 1;
  if (count+6+32 > 255){
    count = 255-6-32;
    endP = 0;
  }
  
  interface->txbuffer[0]=0xfe; // mavlink v1.0 frame
  /* payload len, excluding 6 byte header and 2 byte CRC.
     But we use a 4-byte CRC, so need to add two to count to make packet lengths
     be as expected.
     Note that this construction will result in CRC errors by non-servald
     programmes, which is probably more helpful than otherwise.
  */
  // we need 32 bytes for the parity, but this field assumes
  // that there is a 2 byte CRC, so we can save two bytes
  int len = count+32 - 2;
  interface->txbuffer[1]=len;
  interface->txbuffer[2]=0; // packet sequence
  interface->txbuffer[3]=0x00; // system ID of sender (MAV_TYPE_GENERIC)
  interface->txbuffer[4]=0x40; // component ID of sender: we are reusing this to mark start,end of MDP frames
  if (startP) interface->txbuffer[4]|=0x01;
  if (endP) interface->txbuffer[4]|=0x02;
  interface->txbuffer[5]=MAVLINK_MSG_ID_DATASTREAM; // message ID type of this frame: DATA_STREAM
  // payload follows (we reuse the DATA_STREAM message type parameters)
  ob_get_bytes(interface->tx_packet, &interface->txbuffer[6], count);
  
  encode_rs_8(&interface->txbuffer[2], &interface->txbuffer[6+count], 223 - (count+4));
  interface->tx_bytes_pending=len + 8;
  if (endP){
    ob_free(interface->tx_packet);
    interface->tx_packet=NULL;
    overlay_queue_schedule_next(gettime_ms());
  }
  return 0;
}

int mavlink_heartbeat(unsigned char *frame,int *outlen)
{
  int count=9;
  bzero(frame, count+8);
  
  frame[0]=0xfe; // mavlink v1.0 frame
  // Must be 9 to indicate heartbeat
  frame[1]=count; // payload len, excluding 6 byte header and 2 byte CRC
  frame[2]=0; // packet sequence
  frame[3]=0x00; // system ID of sender (MAV_TYPE_GENERIC)
  frame[4]=0xf1; // component ID of sender (MAV_COMP_ID_UART_BRIDGE)
  // Must be zero to indicate heartbeat
  frame[5]=0; // message ID type of this frame: DATA_STREAM

  // empty payload

  // two-byte CRC follows
  mavlink_crc(frame,count); // automatically adds 6 for header length
  
  *outlen=count+8;
  
  return 0;
}

extern unsigned long long last_rssi_time;
extern int last_radio_rssi;
extern int last_radio_temperature;
extern int last_radio_rxpackets;

int mavlink_parse(struct slip_decode_state *state)
{
  int packet_length=state->mavlink_payload[1];
  if (packet_length==9){
    if (state->mavlink_payload[5]==MAVLINK_MSG_ID_RADIO){
      // we can assume that radio status packets arrive without corruption
      last_radio_rssi=(1.0*state->mavlink_payload[10]-state->mavlink_payload[13])/1.9;
      last_radio_temperature=-999; // doesn't get reported
      last_radio_rxpackets=-999; // doesn't get reported
      if (config.debug.mavlink||gettime_ms()-last_rssi_time>30000) {
	INFOF("Link budget = %+ddB, remote link budget = %+ddB, buffer space = %d%%",
	      last_radio_rssi,
	      (int)((1.0*state->mavlink_payload[11]-state->mavlink_payload[14])/1.9),
	      state->mavlink_payload[12]);
	last_rssi_time=gettime_ms();
      }
    }
    return 0;
  }
  
  int data_bytes = packet_length - (32 - 2);
  
  int errcount=decode_rs_8(&state->mavlink_payload[2], NULL, 0, 223 - (data_bytes + 4));
  if (errcount==-1){
    if (config.debug.mavlink)
      DEBUGF("Reed-Solomon error correction failed");
    state->packet_length=sizeof(state->dst)+1;
    return 0;
  }
  
  if (config.debug.mavlink){
    DEBUGF("Received RS protected message, len: %d, errors: %d, flags:%s%s", 
      data_bytes,
      errcount,
      state->mavlink_payload[4]&0x01?" start":"",
      state->mavlink_payload[4]&0x02?" end":"");
  }
  
  if (state->mavlink_payload[4]&0x01)
    state->packet_length=0;
    
  if (state->packet_length + data_bytes > sizeof(state->dst)){
    if (config.debug.mavlink) 
      DEBUG("Fragmented packet is too long or a previous piece was missed - discarding");
    state->packet_length=sizeof(state->dst)+1;
    return 0;
  }
  
  bcopy(&state->mavlink_payload[6], &state->dst[state->packet_length], data_bytes);
  state->packet_length+=data_bytes;
    
  if (state->mavlink_payload[4]&0x02) {
    if (config.debug.mavlink) 
      DEBUGF("PDU Complete (length=%d)",state->packet_length);
    state->dst_offset=0;
    return 1;
  }
  return 0;
}

int mavlink_decode(struct slip_decode_state *state, uint8_t c)
{
  int ret=0;
  // skip all bytes until the next packet boundary
  if (state->mavlink_payload_offset==0 && c!=0xfe){
    if (config.debug.mavlink)
      DEBUGF("Waiting for valid header, skipped byte 0x%02x",c);
    return 0;
  }
    
  if (state->mavlink_payload_offset==1){
    // check that the length seems to be valid
    // radio heartbeats have length==9
    // RS protected frames must be >= (1 + 32 - 2) bytes
    if (c+8>255 || (c<31 && c!=9)){
      if (config.debug.mavlink)
	DEBUGF("Waiting for valid header, skipped byte 0x%02x",c);
      state->mavlink_payload_offset=0;
      return 0;
    }
  }
  
  state->mavlink_payload[state->mavlink_payload_offset++]=c;
  
  if (state->mavlink_payload_offset >= state->mavlink_payload[1]+8){
    ret = mavlink_parse(state);
    state->mavlink_payload_offset=0;
  }
  
  return ret;
}