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LibrePilot/flight/libraries/ubx_utils.c
2014-09-20 20:58:40 +02:00

78 lines
2.8 KiB
C

/**
******************************************************************************
*
* @file ubx_utils.c
* @author The OpenPilot Team, http://www.openpilot.org Copyright (C) 2014.
* @brief UBX Protocol utilities.
* --
* @see The GNU Public License (GPL) Version 3
*
*****************************************************************************/
/*
* 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 3 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.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include <ubx_utils.h>
bool ubx_getLastSentence(uint8_t *data, uint16_t bufferCount, uint8_t * *lastSentence, uint16_t *length)
{
const uint8_t packet_overhead = UBX_HEADER_LEN + 2;
uint8_t *current = data + bufferCount - packet_overhead;
while (current >= data) {
// look for a ubx a sentence
if (current[0] == UBX_SYN1 && current[1] == UBX_SYN2) {
// check whether it fits the current buffer (whole sentence is into buffer)
uint16_t len = current[4] + (current[5] << 8);
if (len + packet_overhead + current <= data + bufferCount) {
*lastSentence = current;
*length = len + packet_overhead;
return true;
}
}
current--;
}
// no complete sentence found
return false;
}
void ubx_buildPacket(UBXPacket_t *pkt, uint8_t packetClass, uint8_t packetId, uint16_t len)
{
pkt->packet.header.syn1 = UBX_SYN1;
pkt->packet.header.syn2 = UBX_SYN2;
// don't make any assumption on alignments...
((uint8_t *)&pkt->packet.header.len)[0] = len & 0xFF;
((uint8_t *)&pkt->packet.header.len)[1] = (len >> 8) & 0xFF;
pkt->packet.header.class = packetClass;
pkt->packet.header.id = packetId;
ubx_appendChecksum(pkt);
}
void ubx_appendChecksum(UBXPacket_t *pkt)
{
uint8_t chkA = 0;
uint8_t chkB = 0;
uint16_t len = ((uint8_t *)&pkt->packet.header.len)[0] | ((uint8_t *)&pkt->packet.header.len)[1] << 8;
// From class field to the end of payload
for (uint8_t i = 2; i < len + UBX_HEADER_LEN; i++) {
chkA += pkt->binarystream[i];
chkB += chkA;
}
;
pkt->packet.payload[len] = chkA;
pkt->packet.payload[len + 1] = chkB;
}