# 数据类型

有以下数据类型被在通信协议中使用。 协议中的数据类型都是 **小端序**。

## 数据帧组成

|        | 帧头 | 帧头     | 帧头     | 帧头     | 帧头     | 数据区    | 数据区    | 帧尾   |
|---     |---   |---       |---       |---       |---       |---        |---        |---     |
|        | 起始 | 指令类别 | 数据长度 | 流水序号 | 帧头CRC8 | 数据CRC16 | 载荷      | 结束   |
| 字节数 | 1    | 1        | 1        | 1        | 1        | 2         | 1-255     | 1      |
| 数值   | 0xFC | **A**    | **B**    | **C**    | **D**    | 高字节(E), 低字节(E) || 0xFD   |

- **A**: 指令的类别，如下表所示

| 指令类别 | | |
|---|---|---|
| 0x40 | 经过校准的IMU数据 | MSG_IMU |
| 0x41 | AHRS数据 | MSG_AHRS |
| 0x42 | INS/GPS数据 | MSG_INS/GPS |
| 0x58 | 传感器原始数据 | MSG_RAW_GNSS |

- **B**: 载荷的字节数
- **C**: 流水号，每发送一个数据帧数值加一，用于检测数据帧丢包
- **D**: 帧头CRC8校验，计算帧头部分（起始标志 + 指令类别 + 数据长度 + 流水序号）
- **E**: 数据CRC16校验，计算载荷数据的CRC16校验
- **F**: 0xF0 是上位机心跳请求

## CRC8校验

CRC 8校验位：标志位 + 指令类别 + 数据长度 + 流水序号

CRC 8校验程序如下：

```c
static const uint8_t CRC8Table[] = {
	0,  94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
	157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220,
	35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98,
	190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,
	70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7,
	219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154,
	101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36,
	248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185,
	140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205,
	17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80,
	175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238,
	50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115,
	202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139,
	87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22,
	233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168,
	116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53
};
uint8_t CRC8_Table(uint8_t* p, uint8_t counter)
{
	uint8_t crc8 = 0;
	for (int i = 0; i < counter; i++)
	{
		uint8_t value = p[i];
		uint8_t new_index = crc8 ^ value;
		crc8 = CRC8Table[new_index];
	}
	return (crc8);
}
```

CRC8 校验程序调用举例：

```c
uint8_t CRC8 = CRC8_Table(data, data_len);
```

## CRC16校验

CRC 16校验：载荷

CRC 16校验程序如下：

```c
static const uint16_t CRC16Table[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
};
uint16_t CRC16_Table(uint8_t* p, uint8_t counter)
{
	uint16_t crc16 = 0;
	for (int i = 0; i < counter; i++)
	{
		uint8_t value = p[i];
		crc16 = CRC16Table[((crc16 >> 8) ^ value) & 0xff] ^ (crc16 << 8);
	}
	return (crc16);
}
```

CRC16 校验程序调用举例：

```c
uint16_t CRC16 = CRC16_Table(payload, length);
```

## AN数据帧定义与自定义CAN_ID

打开 FDIGroundStation 上位机，连接设备后将 COMM 板块的 CAN 数据输出口设置为 **NAV** 选项后，用户即可通过CAN获取数据，输出数据帧定义与FDILink协议一致，如下表所示。

|        | 帧头 | 帧头     | 帧头     | 帧头     | 帧头     | 数据区    | 数据区    | 帧尾   |
|---     |---   |---       |---       |---       |---       |---        |---        |---     |
|        | 起始 | 指令类别 | 数据长度 | 流水序号 | 帧头CRC8 | 数据CRC16 | 载荷      | 结束   |
| 字节数 | 1    | 1        | 1        | 1        | 1        | 2         | 1-255     | 1      |
| 数值   | 0xFC | **A**    | **B**    | **C**    | **D**    | 高字节(E), 低字节(E) || 0xFD   |