gyro_board/src/usb/data_struct.h

// This isn't really a header file. It's designed to be #included directly into
// other code (possibly in a namespace or whatever), so it doesn't have include
// guards.
// This means that it can not #include anything else because it (sometimes) gets
// #included inside a namespace.
// <stdint.h> must be #included by the containing file.
// In the gyro board code, fill_packet.h #includes this file.
// In the fitpc code, frc971/input/gyro_board_data.h #includes this file.

#pragma pack(push, 1)
// Be careful with declaration order in here. ARM doesn't like unaligned
// accesses!
struct DATA_STRUCT_NAME {
  int64_t gyro_angle;

  // In units of 100,000 counts/second.
  uint64_t timestamp;

  union {
    struct {
      // This is a counter that gets incremented with each packet sent.
      uint32_t sequence;

      // Which robot (+version) the gyro board is sending out data for.
      // We should keep this in the same place for all gyro board software
      // versions so that the fitpc can detect when it's reading from a gyro
      // board set up for a different robot (or version) than it is.
      // The numbers listed below each robot are the values that have been used
      // for it.
      //
      // 2013 competition/practice robot
      //   0
      //   2 added battery measurement + drivetrain analog hall effects
      // 2013 3rd robot
      //   1
      uint8_t robot_id;
      // This information should also be kept in the same place from year to
      // year so that the fitpc code can record the dip switch values when it
      // detects the wrong robot id to make debugging easier.
      union {
        struct {
          uint8_t dip_switch0 : 1;
          uint8_t dip_switch1 : 1;
          uint8_t dip_switch2 : 1;
          uint8_t dip_switch3 : 1;
        };
        uint8_t dip_switches;
      };
      struct {
        // If the current gyro_angle has been not updated because of a bad
        // reading from the sensor.
        uint8_t old_gyro_reading : 1;
        // If we're not going to get any more good gyro_angles.
        uint8_t bad_gyro : 1;
      };
    };
    uint64_t header;
  };

  // We are 64-bit aligned at this point.

  union {
    struct {
      int32_t left_drive;
      int32_t right_drive;
      int32_t shooter_angle;
      int32_t shooter;
      int32_t indexer;
      int32_t wrist;

      int32_t capture_top_rise;
      int32_t capture_top_fall;
      int32_t capture_bottom_fall_delay;
      int32_t capture_wrist_rise;
      int32_t capture_shooter_angle_rise;

      uint16_t battery_voltage;
      uint16_t left_drive_hall;
      uint16_t right_drive_hall;

      int8_t top_rise_count;

      int8_t top_fall_count;

      int8_t bottom_rise_count;

      int8_t bottom_fall_delay_count;
      int8_t bottom_fall_count;

      int8_t wrist_rise_count;

      int8_t shooter_angle_rise_count;

      struct {
        uint8_t wrist_hall_effect : 1;
        uint8_t angle_adjust_bottom_hall_effect : 1;
        uint8_t top_disc : 1;
        uint8_t bottom_disc : 1;
        uint8_t loader_top : 1;
        uint8_t loader_bottom : 1;
      };
    } main;
    
    struct {
      union {
        struct {
        };
        uint16_t booleans;
      };
    } bot3;
  };
};
#pragma pack(pop)

// This is how big the isochronous packets that we're going to send are.
// This number is more painful to change than the actual size of the struct
// because the code on both ends has to agree on this (or at least that's what
// Brian found empirically 2013-10-24).
#define DATA_STRUCT_SEND_SIZE 128

#ifdef __cplusplus
// TODO(brians): Consider using C1X's _Static_assert once we have a compiler
// (GCC 4.6) + flags that support it.
static_assert(sizeof(DATA_STRUCT_NAME) <= DATA_STRUCT_SEND_SIZE,
              "The sensor data structure is too big.");
#endif  // defined(__cplusplus)