# Ports

* `ROBOT_SDK_PORT_MIN = 10100`
* `ROBOT_SDK_PORT_MAX = 10500`
* `ROBOT_DEVICE_PORT = 20020`
* `ROBOT_PROXY_PORT = 30030`
* `ROBOT_BROADCAST_PORT = 40927`
* `ROBOT_DEFAULT_WIFI_ADDR = 192.168.2.1`

# Direct WIFI connection

Send a `SetSdkConnection` message to `192.168.2.1:30030` containing local IP
address (`0.0.0.0` is fine) and a random port between `10100` and `10500`. The
Robomaster responds with a state, which should be 2, and the IP address
`192.168.2.24` that the client should use. The client will then send further
messages to `192.168.2.1:20020` via `192.168.2.24:<random port>`.

# Commands

* UTF-8 encoded
* command
* version
* quit

[1]: https://github.com/dji-sdk/RoboMaster-SDK/blob/v0.1.2/sample_code/RoboMasterEP/connection/network/robot_connection.py
[2]: https://github.com/SMerrony/tello/blob/master/messages.go

# Message Format

All big-endian unless otherwise noted.

## Header

The preamble `0x55` indicates the start of every message and is part of the
message header along with the length and a checksum of the header. A header is
always 4 bytes long.

| bytes | description |
|-------|-------------|
| 1     | `0x55` preamble |
| 2     | length of message |
| 1     | 8-bit CRC   |

The CRC is a checksum of the preamble and message length together. The length
in bytes is of the entire message including the header.

## Body

The data is always at least one byte.

| bytes | description |
|-------|-------------|
| 1     | sender      |
| 1     | receiver    |
| 2     | seq ID      |
| 1     | attri       |
| 1     | cmdset      |
| 1     | cmdid       |
| >1    | data        |
| 2     | 16-bit CRC  |

The last two bits of the attri byte starting from the LSB represent if the
message is an ack and if an ack is needed. The other bits in the byte are
unused. Any request can specify if an ack is required, or not. If no ack is
required, the drone will not send a response.

| bit | set         | unset |
|-----|-------------|-------|
| 8   | is ack      | enc   |
| 7   | ack needed  | no ack needed |

### TODO

* What is a seq ID?
* What is the format of sender and receiver?
  * may not actually matter
  * index always seems to be 0
  * `index * 32 + host`
  * sender is `_client.hostbyte`
* What is the difference between cmdid and cmdset?

# Messages

| name | cmdset | cmdid  | bytes |
|------|--------|--------|-------|
| led  | `0x3f` | `0x33` | 15    |
| set sdk connection  | `0x3f` | `0xd4` | 10    |

## SetSdkConnection

| bytes | description |
|-------|-------------|
| 1     | control     |
| 1     | host        |
| 1     | connection  |
| 1     | protocol    |
| 4     | IP address  |

Response message.

| bytes | description |
|-------|-------------|
| 1     | Return code |
| 1     | state       |
| 4     | IP address  |

What is `config_ip`? What is `state`?

## LED

| bytes | description |
|-------|-------------|
| 4     | comp mask   |
| 2     | LED mask    |
| 1     | ctrl & effect mode |
| 1     | red         |
| 1     | green       |
| 1     | blue        |
| 1     | loop        |
| 2     | t1          |
| 2     | t2          |

Control and effect modes share one byte, in MSB and LSB respectively.