dispatch.h

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#ifndef _DISPATCH_H
#define _DISPATCH_H
#include <stdint.h>

#pragma pack(push, 1)
typedef union {
  uint8_t bytes[8];
  struct {
    uint32_t gps_minutes;
    uint8_t num_sats;
    uint8_t position_mode;
    uint8_t velocity_mode;
    uint8_t orientation_mode;
  } chan0;
  struct {
    uint16_t acc_position_north; // 1e-3 m
    uint16_t acc_position_east;
    uint16_t acc_position_down;
    uint8_t age;
  } chan3;
  struct {
    uint16_t acc_velocity_north; // 1e-3 m/s
    uint16_t acc_velocity_east;
    uint16_t acc_velocity_down;
    uint8_t age;
  } chan4;
  struct {
    uint16_t acc_heading; // 1e-5 rad
    uint16_t acc_pitch;
    uint16_t acc_roll;
    uint8_t age;
  } chan5;
  struct {
    int16_t base_station_age;
    int8_t base_station_id[4];
  } chan20;
  struct {
    uint16_t delay_ms;
  } chan23;
  struct {
    uint8_t heading_quality; // 0:None 1:Poor 2:RTK Float 3:RTK Integer
  } chan27;
  struct {
    int16_t heading_misalignment_angle; // 1e-4 rad
    uint16_t heading_misalignment_accuracy; // 1e-4 rad
    uint16_t :16;
    uint8_t valid;
  } chan37;
  struct {
    int16_t undulation; // 5e-3 m
    uint8_t HDOP; // 1e-1
    uint8_t PDOP; // 1e-1
  } chan48;
} Channel;
typedef struct {
  uint8_t sync;
  uint16_t time;
  int32_t accel_x :24; // 1e-4 m/s^2
  int32_t accel_y :24; // 1e-4 m/s^2
  int32_t accel_z :24; // 1e-4 m/s^2
  int32_t gyro_x :24; // 1e-5 rad/s
  int32_t gyro_y :24; // 1e-5 rad/s
  int32_t gyro_z :24; // 1e-5 rad/s
  uint8_t nav_status;
  uint8_t chksum1;
  double latitude;
  double longitude;
  float altitude;
  int32_t vel_north :24; // 1e-4 m/s
  int32_t vel_east :24; // 1e-4 m/s
  int32_t vel_down :24; // 1e-4 m/s
  int32_t heading :24; // 1e-6 rad
  int32_t pitch :24; // 1e-6 rad
  int32_t roll :24; // 1e-6 rad
  uint8_t chksum2;
  uint8_t channel;
  Channel chan;
  uint8_t chksum3;
} Packet;
enum {
  MODE_NONE = 0,
  MODE_SEARCH = 1,
  MODE_DOPPLER = 2,
  MODE_SPS = 3,
  MODE_DIFFERENTIAL = 4,
  MODE_RTK_FLOAT = 5,
  MODE_RTK_INTEGER = 6,
  MODE_WAAS = 7,
  MODE_OMNISTAR_VBS = 8,
  MODE_OMNISTAR_HP = 9,
  MODE_NO_DATA = 10,
  MODE_BLANKED = 11,
  MODE_DOPPLER_PP = 12,
  MODE_SPS_PP = 13,
  MODE_DIFFERENTIAL_PP = 14,
  MODE_RTK_FLOAT_PP = 15,
  MODE_RTK_INTEGER_PP = 16,
  MODE_OMNISTAR_XP = 17,
  MODE_CDGPS = 18,
  MODE_NOT_RECOGNISED = 19,
  MODE_DOPPLER_GX = 20,
  MODE_SPS_GX = 21,
  MODE_DIFFERENTIAL_GX = 22,
  MODE_RTK_FLOAT_GX = 23,
  MODE_RTK_INTEGER_GX = 24,
  MODE_DOPPLER_IX = 25,
  MODE_SPS_IX = 26,
  MODE_DIFFERENTIAL_IX = 27,
  MODE_RTK_FLOAT_IX = 28,
  MODE_RTK_INTEGER_IX = 29,
  MODE_PPP_CONVERGING = 30,
  MODE_PPP = 31,
  MODE_UNKNOWN = 32
};
#pragma pack(pop)

static bool validatePacket(const Packet *packet) {
  if (packet->sync == 0xE7) {
    const uint8_t *ptr = (uint8_t*)packet;
    uint8_t chksum = 0;
    for (unsigned int i = 1; i < sizeof(Packet) - 1; i++) {
      chksum += ptr[i];
    }
    return chksum == packet->chksum3;
  }
  return false;
}

#define BUILD_ASSERT(cond) do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)
static void dispatchAssertSizes() {
  BUILD_ASSERT(8 == sizeof(Channel));
  BUILD_ASSERT(72 == sizeof(Packet));
}
#undef BUILD_ASSERT

#endif // _DISPATCH_H