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Reverse byte ordering of CRC in packet mode in M17 modem #1891

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merged 1 commit into from
Nov 15, 2023
Merged

Reverse byte ordering of CRC in packet mode in M17 modem #1891

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4 changes: 2 additions & 2 deletions modemm17/M17Modulator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -309,8 +309,8 @@ struct MODEMM17_API M17Modulator
if (last_packet)
{
packet_assembly[25] = 0x80 | ((packet_size+2)<<2); // sent packet size includes CRC
packet_assembly[packet_size] = crc_.get_bytes()[1];
packet_assembly[packet_size+1] = crc_.get_bytes()[0];
packet_assembly[packet_size] = crc_.get_bytes()[0];
packet_assembly[packet_size+1] = crc_.get_bytes()[1];
}
else
{
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2 changes: 1 addition & 1 deletion plugins/channelrx/demodm17/m17demodprocessor.cpp
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Expand Up @@ -328,7 +328,7 @@ bool M17DemodProcessor::decode_packet(modemm17::M17FrameDecoder::packet_buffer_t
crc16(*it);
}

uint16_t calcChecksum = crc16.get_bytes()[0] + (crc16.get_bytes()[1]<<8);
uint16_t calcChecksum = crc16.get_bytes()[1] + (crc16.get_bytes()[0]<<8);
uint16_t xmitChecksum = m_currentPacket.back() + (m_currentPacket.end()[-2]<<8);

if (calcChecksum == xmitChecksum) // (checksum == 0x0f47)
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