ardupilot/libraries/SITL/SIM_GPS_SBF.cpp

#include "SIM_config.h"

#if AP_SIM_GPS_SBF_ENABLED

#include "SIM_GPS_SBF.h"

#include <SITL/SITL.h>
#include <time.h>

using namespace SITL;

static const uint16_t CRC16_LOOK_UP[256] = {
    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129,
    0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210, 0x3273, 0x2252,
    0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c,
    0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672,
    0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738,
    0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861,
    0x2802, 0x3823, 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
    0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5,
    0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b,
    0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9,
    0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3,
    0x5004, 0x4025, 0x7046, 0x6067, 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c,
    0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3,
    0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
    0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676,
    0x4615, 0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c,
    0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, 0x4a75, 0x5a54, 0x6a37, 0x7a16,
    0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b,
    0x9de8, 0x8dc9, 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36,
    0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
};

void GPS_SBF::send_sbf(uint16_t msgid, uint8_t *buf, uint16_t size)
{
    if ((size % 4) != 0) {
        AP_HAL::panic("Invalid SBF packet length");
    }

    //HEADER
    const uint8_t PREAMBLE1 = 0x24;
    const uint8_t PREAMBLE2 = 0x40;
    uint8_t hdr[8];
    uint16_t crc = 0;
    hdr[0] = PREAMBLE1;
    hdr[1] = PREAMBLE2;
    hdr[4] = msgid & 0xFF;
    hdr[5] = (msgid >> 8) & 0xFF;
    hdr[6] = (size+8) & 0xFF;
    hdr[7] = ((size+8) >> 8) & 0xFF;
    for (uint8_t i = 4; i<8; i++) {
        crc = (crc << 8) ^ CRC16_LOOK_UP[uint8_t((crc >> 8) ^ hdr[i])]; //include id and length
    }
    for (uint16_t i = 0; i<size; i++) {
        crc = (crc << 8) ^ CRC16_LOOK_UP[uint8_t((crc >> 8) ^ buf[i])];
    }
    hdr[2] = crc & 0xFF;
    hdr[3] = (crc >> 8) & 0xFF;

    write_to_autopilot((char*)hdr, sizeof(hdr));
    write_to_autopilot((char*)buf, size);
}

void GPS_SBF::publish(const GPS_Data *d) {
    publish_PVTGeodetic(d);
    publish_DOP(d);
}

// public PVTGeodetic message, ID 4007
void GPS_SBF::publish_PVTGeodetic(const GPS_Data *d)
{
    const double DNU_DOUBLE = -2e10;
    const float DNU_FLOAT = -2e10;
    const uint8_t DNU_UINT8 = 255;
    const uint16_t DNU_UINT16 = 65535;

    struct PACKED timestamp_t {
        uint32_t tow;
        uint16_t wnc;
    };

    struct PACKED sbf_pvtGeod_t
    {
        timestamp_t time_stamp;
        uint8_t mode;
        uint8_t error;
        double latitude;
        double longitude;
        double height;
        float undulation;
        float vn;
        float ve;
        float vu;
        float cog;
        double rxclkbias;
        float rxclkdrift;
        uint8_t timesystem;
        uint8_t datum;
        uint8_t nrsv;
        uint8_t wacorrinfo;
        uint16_t referenceid;
        uint16_t meancorrage;
        uint64_t signalinfo;
        uint8_t alertflag;
        uint8_t __PADDING__[3];  // packets must be zero-mod-4
    } pvtGeod_buf {} ;
    assert_storage_size<sbf_pvtGeod_t, 84> assert_storage_size_pvt_Geod_buf;
    (void)assert_storage_size_pvt_Geod_buf;

    const uint16_t PVTGEO_0_MSG_ID = 0x0FA7;    

    const auto gps_tow = gps_time();
    pvtGeod_buf.time_stamp.tow = gps_tow.ms;
    pvtGeod_buf.time_stamp.wnc = gps_tow.week;
    
    pvtGeod_buf.mode = 4; //Mode: default to rtk fixed
    pvtGeod_buf.error= 0; //Error: no error
    pvtGeod_buf.latitude = radians(_sitl->state.latitude);
    pvtGeod_buf.longitude = radians(_sitl->state.longitude);
    pvtGeod_buf.height = d->altitude;
    pvtGeod_buf.undulation = DNU_DOUBLE;
    pvtGeod_buf.vn = d->speedN;
    pvtGeod_buf.ve = d->speedE;
    pvtGeod_buf.vu = -d->speedD;
    pvtGeod_buf.cog = degrees(d->ground_track_rad());
    pvtGeod_buf.rxclkbias = DNU_DOUBLE;
    pvtGeod_buf.rxclkdrift = DNU_FLOAT;
    pvtGeod_buf.timesystem = DNU_UINT8; 
    pvtGeod_buf.datum = DNU_UINT8; 
    pvtGeod_buf.nrsv = d->num_sats;
    pvtGeod_buf.wacorrinfo = 0; //default value
    pvtGeod_buf.referenceid = DNU_UINT16; 
    pvtGeod_buf.meancorrage = DNU_UINT16; 
    pvtGeod_buf.signalinfo = 0;
    pvtGeod_buf.alertflag = 0;

    send_sbf(PVTGEO_0_MSG_ID, (uint8_t*)&pvtGeod_buf, sizeof(pvtGeod_buf));
}

// public DOP message, ID 4001
void GPS_SBF::publish_DOP(const GPS_Data *d)
{
    struct PACKED timestamp_t {
        uint32_t tow;
        uint16_t wnc;
    };

    const auto gps_tow = gps_time();

    // swiped from the driver:
    const struct PACKED {
        timestamp_t time_stamp;
        uint8_t NrSV;
        uint8_t Reserved;
        uint16_t PDOP;
        uint16_t TDOP;
        uint16_t HDOP;
        uint16_t VDOP;
        float HPL;
        float VPL;
        // uint8_t __PADDING__[2];
    } packet {
        { gps_tow.ms, gps_tow.week },  // timestamp
        17,  // NrSV
        0,  // reserved
        1,  // PDOP
        1,  // TDOP
        1,  // HDOP
        1,  // VDOP
        1.0,  // HPL
        1.0  // VPL
    };

    send_sbf(4001, (uint8_t*)&packet, sizeof(packet));
}

#endif //AP_SIM_GPS_SBF_ENABLED