src/main/rx/frsky_crc.c

   1 /*
   2  * This file is part of Cleanflight and Betaflight.
   3  *
   4  * Cleanflight and Betaflight are free software. You can redistribute
   5  * this software and/or modify this software under the terms of the
   6  * GNU General Public License as published by the Free Software
   7  * Foundation, either version 3 of the License, or (at your option)
   8  * any later version.
   9  *
  10  * Cleanflight and Betaflight are distributed in the hope that they
  11  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  12  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  13  * See the GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this software.
  17  *
  18  * If not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <stdbool.h>
  22 #include <stdint.h>
  23
  24 #include "platform.h"
  25
  26 #include "rx/frsky_crc.h"
  27
  28 void frskyCheckSumStep(uint16_t *checksum, uint8_t byte)
  29 {
  30     *checksum += byte;
  31 }
  32
  33 void frskyCheckSumFini(uint16_t *checksum)
  34 {
  35     while (*checksum > 0xFF) {
  36         *checksum = (*checksum & 0xFF) + (*checksum >> 8);
  37     }
  38
  39     *checksum = 0xFF - *checksum;
  40 }
  41
  42 static uint8_t frskyCheckSum(uint8_t *data, uint8_t length)
  43 {
  44     uint16_t checksum = 0;
  45     for (unsigned i = 0; i < length; i++) {
  46         frskyCheckSumStep(&checksum, *data++);
  47     }
  48     frskyCheckSumFini(&checksum);
  49     return checksum;
  50 }
  51
  52 bool frskyCheckSumIsGood(uint8_t *data, uint8_t length)
  53 {
  54     return !frskyCheckSum(data, length);
  55 }