Line data    Source code

       1             : /*
       2             :  * This file is free software: you can redistribute it and/or modify it
       3             :  * under the terms of the GNU General Public License as published by the
       4             :  * Free Software Foundation, either version 3 of the License, or
       5             :  * (at your option) any later version.
       6             :  *
       7             :  * This file is distributed in the hope that it will be useful, but
       8             :  * WITHOUT ANY WARRANTY; without even the implied warranty of
       9             :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
      10             :  * See the GNU General Public License for more details.
      11             :  *
      12             :  * You should have received a copy of the GNU General Public License along
      13             :  * with this program.  If not, see <http://www.gnu.org/licenses/>.
      14             :  */
      15             : /*
      16             :   soft serial receive implementation, based on pulse width inputs
      17             :  */
      18             : 
      19             : #include "SoftSerial.h"
      20             : #include <AP_Math/crc.h>
      21             : #include <stdio.h>
      22             : 
      23       20940 : SoftSerial::SoftSerial(uint32_t _baudrate, serial_config _config) :
      24       20940 :     baudrate(_baudrate),
      25       20940 :     half_bit((1000000U / baudrate)/2),
      26       20940 :     config(_config)
      27             : {
      28       20940 :     switch (config) {
      29       14658 :     case SERIAL_CONFIG_8N1:
      30             :     case SERIAL_CONFIG_8N1I:
      31       14658 :         data_width = 8;
      32       14658 :         byte_width = 10;
      33       14658 :         stop_mask = 0x200;
      34       14658 :         break;
      35        6282 :     case SERIAL_CONFIG_8E2I:
      36        6282 :         data_width = 9;
      37        6282 :         byte_width = 12;
      38        6282 :         stop_mask = 0xC00;
      39        6282 :         break;
      40             :     }
      41       20940 : }
      42             : 
      43             : /*
      44             :   process a pulse made up of a width of values at high voltage
      45             :   followed by a width at low voltage
      46             :  */
      47           0 : bool SoftSerial::process_pulse(uint32_t width_high, uint32_t width_low, uint8_t &byte)
      48             : {
      49             :     // convert to bit widths, allowing for a half bit error
      50           0 :     uint16_t bits_high = ((width_high+half_bit)*baudrate) / 1000000;
      51           0 :     uint16_t bits_low = ((width_low+half_bit)*baudrate) / 1000000;
      52             : 
      53           0 :     byte_timestamp_us = timestamp_us;
      54           0 :     timestamp_us += (width_high + width_low);
      55             : 
      56           0 :     if (bits_high == 0 || bits_low == 0) {
      57             :         // invalid data
      58           0 :         goto reset;
      59             :     }
      60             : 
      61           0 :     if (bits_high >= byte_width) {
      62             :         // if we have a start bit and a stop bit then we can have at
      63             :         // most 9 bits in high state for data. The rest must be idle
      64             :         // bits
      65           0 :         bits_high = byte_width-1;
      66             :     }
      67             : 
      68           0 :     if (state.bit_ofs == 0) {
      69             :         // we are in idle state, waiting for first low bit. swallow
      70             :         // the high bits
      71           0 :         bits_high = 0;
      72             :     }
      73             : 
      74           0 :     state.byte |= ((1U<<bits_high)-1) << state.bit_ofs;
      75             : 
      76           0 :     state.bit_ofs += bits_high + bits_low;
      77             : 
      78           0 :     if (state.bit_ofs >= byte_width) {
      79             :         // check start bit
      80           0 :         if ((state.byte & 1) != 0) {
      81           0 :             goto reset;
      82             :         }
      83             :         // check stop bits
      84           0 :         if ((state.byte & stop_mask) != stop_mask) {
      85           0 :             goto reset;
      86             :         }
      87           0 :         if (config == SERIAL_CONFIG_8E2I) {
      88             :             // check parity
      89           0 :             if (parity((state.byte>>1)&0xFF) != (state.byte&0x200)>>9) {
      90           0 :                 goto reset;
      91             :             }
      92             :         }
      93             : 
      94           0 :         byte = ((state.byte>>1) & 0xFF);
      95           0 :         state.byte >>= byte_width;
      96           0 :         state.bit_ofs -= byte_width;
      97           0 :         if (state.bit_ofs > byte_width) {
      98           0 :             state.byte = 0;
      99           0 :             state.bit_ofs = bits_low;
     100             :         }
     101             :         // swallow idle bits
     102           0 :         while (state.bit_ofs > 0 && (state.byte & 1)) {
     103           0 :             state.bit_ofs--;
     104           0 :             state.byte >>= 1;
     105             :         }
     106           0 :         return true;
     107             :     }
     108           0 :     return false;
     109             : 
     110           0 : reset:
     111           0 :     state.byte = 0;
     112           0 :     state.bit_ofs = 0;
     113             : 
     114           0 :     return false;
     115             : }
     116             :