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AIS Packet refactor, consolidating duplicate packet length code.

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This commit is contained in:
Jared Boone 2015-12-08 11:14:00 -08:00
parent 7cded79b59
commit af74daf092
2 changed files with 31 additions and 30 deletions
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54
firmware/application/app_ais.cpp
View File

@ -130,23 +130,6 @@ struct PacketTooLong {
} }
}; };
struct CRCCheck {
bool operator()(const ::Packet& packet) {
const size_t fcs_length = 16;
const size_t data_and_fcs_length = packet.size() - 7;
const size_t data_length = data_and_fcs_length - fcs_length;
CRCFieldReader field_crc { packet };
CRC<uint16_t> ais_fcs { 0x1021, 0xffff, 0xffff };
for(size_t i=0; i<data_length; i+=8) {
ais_fcs.process_byte(field_crc.read(i, 8));
}
return ais_fcs.checksum() == field_crc.read(data_length, fcs_length);
}
};
static std::string format_latlon_normalized(const int32_t normalized) { static std::string format_latlon_normalized(const int32_t normalized) {
const int32_t t = (normalized * 5) / 3; const int32_t t = (normalized * 5) / 3;
const int32_t degrees = t / (100 * 10000); const int32_t degrees = t / (100 * 10000);
@ -200,30 +183,21 @@ size_t Packet::length() const {
} }
bool Packet::is_valid() const { bool Packet::is_valid() const {
// Subtract end flag (8 bits) - one unstuffing bit (occurs during end flag). if( data_and_fcs_length() < 38 ) {
const size_t data_and_fcs_length = length() - 7;
if( data_and_fcs_length < 38 ) {
return false; return false;
} }
const size_t extra_bits = data_and_fcs_length & 7; const size_t extra_bits = data_and_fcs_length() & 7;
if( extra_bits != 0 ) { if( extra_bits != 0 ) {
return false; return false;
} }
const size_t data_length = data_and_fcs_length - 16;
PacketLengthValidator packet_length_valid; PacketLengthValidator packet_length_valid;
if( !packet_length_valid(message_id(), data_length) ) { if( !packet_length_valid(message_id(), data_length()) ) {
return false; return false;
} }
CRCCheck crc_ok; return crc_ok();
if( !crc_ok(packet_) ) {
return false;
}
return true;
} }
rtc::RTC Packet::received_at() const { rtc::RTC Packet::received_at() const {
@ -285,6 +259,26 @@ Longitude Packet::longitude(const size_t start_bit) const {
return static_cast<int32_t>(field_.read(start_bit, 28) << 4) / 16; return static_cast<int32_t>(field_.read(start_bit, 28) << 4) / 16;
} }
bool Packet::crc_ok() const {
CRCFieldReader field_crc { packet_ };
CRC<uint16_t> ais_fcs { 0x1021, 0xffff, 0xffff };
for(size_t i=0; i<data_length(); i+=8) {
ais_fcs.process_byte(field_crc.read(i, 8));
}
return (ais_fcs.checksum() == field_crc.read(data_length(), fcs_length));
}
size_t Packet::data_and_fcs_length() const {
// Subtract end flag (8 bits) - one unstuffing bit (occurs during end flag).
return length() - 7;
}
size_t Packet::data_length() const {
return data_and_fcs_length() - fcs_length;
}
} /* namespace ais */ } /* namespace ais */
} /* namespace baseband */ } /* namespace baseband */

7
firmware/application/app_ais.hpp
View File

@ -95,10 +95,17 @@ public:
Latitude latitude(const size_t start_bit) const; Latitude latitude(const size_t start_bit) const;
Longitude longitude(const size_t start_bit) const; Longitude longitude(const size_t start_bit) const;
bool crc_ok() const;
private: private:
const ::Packet packet_; const ::Packet packet_;
const rtc::RTC received_at_; const rtc::RTC received_at_;
const FieldReader field_; const FieldReader field_;
const size_t fcs_length = 16;
size_t data_and_fcs_length() const;
size_t data_length() const;
}; };
} /* namespace ais */ } /* namespace ais */