SPI        UART
DWM1000 <===> STM32 <===> Host(PC/Android/MCU)

类SLIP转义:
0xDB为转义标志, '\n'为结束标志
0xDB被转义成0xDB, 0xDC
'\n'被转义成0xDB, 0xDD


MSG
+-------+--------+--------+-----------------+
| Bytes |    0   |    1   |        N        |
+-------+--------+--------+-----------------+
|  def  |  TYPE  |  LEN   | Payload(126MAX) |
+-------+--------+--------+-----------------+

消息最大长度为128 (126 + 2) 字节
  1. 消息类型 Type
    0x00: 消息
    0x01: 测距以及Beacon
    0x02: 设置MAC地址以及PANID
    0x03: RESET
    0x04: Auto Beacon
    0x05: Log Msg
  2. Packet Length
    Payload长度，以无符号8位整型(unsigned char)表示
  3. Payload
    不同消息参照不同的内容

0x00 消息

Payload的基础格式参照`IEEE 802.15.4a`标准。
我们尽量采用短地址以节约资源。
Frame Control: 一定要采用 0x41, 0x88
Sequence Num: Place Holder
Dest PANID, Dest Addr, Src Addr: 注意字节序，如果目标地址设置成了"KI" 则要填 "IK"
FCS: 自动添加，但是需要留位置，两个0x00就行。
原则上来说，这些都是在驱动层来处理的，app层无需关心。
+---------------+--------------+------------+-----------+-----------+----------+---------+
| Frame Control | Sequence Num | Dest PANID | Dest Addr | Src Addr  |  Payload |   FCS   |
+---------------+--------------+------------+-----------+-----------+----------+---------+
| 2 Bytes       | 1 Byte       | 2 Bytes    | 2 Bytes   | 2 Bytes   | Var Bytes| 2 Bytes |
+---------------+--------------+------------+-----------+-----------+----------+---------+
| 0x41, 0x88    | 0x00         | 0xDECA     | "YU"      | "KI"      | "Hello!" |   Auto  |
+---------------+--------------+------------+-----------+-----------+----------+---------+

0x01 测距以及Beacon

不需要填len
Payload为空则为广播。
若Payload为目标PANID以及MAC地址，则单播。(尚未实现)

接收到的下位机到PC的Payload消息格式:
+------------+---------------+
|    Addr    |   Distance    |
+------------+---------------+
|  2 Bytes   |   4 bytes     |
+------------+---------------+
| 0xCA, 0xDE | 低字节在前(int)|
+------------+---------------+

由于下位机的浮点数处理有点问题，此处得到的距离并不是真正的距离。
真实距离 = distance / 2.0 * 1.0 / 499.2e6 / 128.0 * 299702547

0x02 设置MAC地址以及PANID

Payload 格式:
+------------+-----------+
|    PANID   |   Addr    |
+------------+-----------+
|  2 Bytes   |  2 Bytes  |
+------------+-----------+
| 0xCA, 0xDE | 'U', 'Y'  |
+------------+-----------+

0x03 RESET:
尚未实现

0x04 Auto Beacon:

Payload 格式:
+------------+
|   Enable   |
+------------+
|  1 Bytes   |
+------------+
|0x00 or 0x01|
+------------+

802.15.4a Frame:
+---------------+--------------+------------+-----------+-----------+----------+-----------+---------+
| Frame Control | Sequence Num | Dest PANID | Dest Addr | Src PANID | Src Addr |  Payload  |   FCS   |
+---------------+--------------+------------+-----------+-----------+----------+-----------+---------+
| 2 Bytes       | 1 Byte       | 2 Bytes    | 8 Bytes   | 2 Bytes   | 8 Bytes  | Var Bytes | 2 Bytes |
+---------------+--------------+------------+-----------+-----------+----------+-----------+---------+

Frame Control:
+------+---+---+---+----------+---------+--------+----------+---+---+---+-----+-----+----+----+-----+----+
| Bits | 0 | 1 | 2 |    3     |    4    |   5    |    6     | 7 | 8 | 9 | 10  | 11  | 12 | 13 | 14  | 15 |
+------+---+---+---+----------+---------+--------+----------+---+---+---+-----+-----+----+----+-----+----+
|      | Frame     | Security | Frame   | ACK    | PANID    | Reserved  | Dest Addr | Frame   | Src Addr |
|      | Type      | Enabled  | Pending | Requst | Compress |           | Mode      | Version | Mode     |
+------+-----------+----------+---------+--------+----------+-----------+-----------+---------+----------+
1. Frame Type
        100 - Location Service (802.15.4a Reserved).
                Then the first byte of Payload is used to identify the LS message type.
                0x00 - LS Req
                        Request for Location Service.
                0x01 - LS ACK
                        ACK for LS Req, and mark the receive time of LS Req(T_Req) and the sent time of LS ACK(T_ACK).
                0x02 - LS Data
                        Return T_ACK - T_Req.
                0x03 - LS Information Return
                        Return the distance data to the ACK node.
                0x04 - LS Forward
                        Forward the Location data to a specific node.
2. Other Fields
        Please reference 802.15.4a.