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78 lines
2.8 KiB
C
78 lines
2.8 KiB
C
/**
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******************************************************************************
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*
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* @file ubx_utils.c
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* @author The OpenPilot Team, http://www.openpilot.org Copyright (C) 2014.
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* @brief UBX Protocol utilities.
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* --
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* @see The GNU Public License (GPL) Version 3
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*
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*****************************************************************************/
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/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <ubx_utils.h>
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bool ubx_getLastSentence(uint8_t *data, uint16_t bufferCount, uint8_t * *lastSentence, uint16_t *length)
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{
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const uint8_t packet_overhead = UBX_HEADER_LEN + 2;
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uint8_t *current = data + bufferCount - packet_overhead;
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while (current >= data) {
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// look for a ubx a sentence
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if (current[0] == UBX_SYN1 && current[1] == UBX_SYN2) {
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// check whether it fits the current buffer (whole sentence is into buffer)
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uint16_t len = current[4] + (current[5] << 8);
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if (len + packet_overhead + current <= data + bufferCount) {
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*lastSentence = current;
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*length = len + packet_overhead;
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return true;
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}
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}
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current--;
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}
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// no complete sentence found
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return false;
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}
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void ubx_buildPacket(UBXPacket_t *pkt, uint8_t packetClass, uint8_t packetId, uint16_t len)
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{
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pkt->packet.header.syn1 = UBX_SYN1;
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pkt->packet.header.syn2 = UBX_SYN2;
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// don't make any assumption on alignments...
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((uint8_t *)&pkt->packet.header.len)[0] = len & 0xFF;
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((uint8_t *)&pkt->packet.header.len)[1] = (len >> 8) & 0xFF;
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pkt->packet.header.class = packetClass;
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pkt->packet.header.id = packetId;
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ubx_appendChecksum(pkt);
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}
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void ubx_appendChecksum(UBXPacket_t *pkt)
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{
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uint8_t chkA = 0;
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uint8_t chkB = 0;
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uint16_t len = ((uint8_t *)&pkt->packet.header.len)[0] | ((uint8_t *)&pkt->packet.header.len)[1] << 8;
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// From class field to the end of payload
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for (uint8_t i = 2; i < len + UBX_HEADER_LEN; i++) {
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chkA += pkt->binarystream[i];
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chkB += chkA;
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}
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;
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pkt->packet.payload[len] = chkA;
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pkt->packet.payload[len + 1] = chkB;
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}
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