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The MicroCART project uses custom packets to communicate with the quad. This may seem complex at first
but the structure of all packets is the same it is just the way the data is formatted that changes
between packets.
## Introduction ##
All packets are the same in the sense that they have consistent headers with a start character and all end with a checksum as well as
a end character. The basic structure is shown below.
| Index | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|:-----------------:|:---------------:|:------------:|:----------:|:-----------:|:----:|:--------:|:-------------:|
| Message Parameter | Begin Character | Message Type | Message ID | Data Length | Data | Checksum | End Character |
| Bytes | 1 | 2 | 2 | 2 | var | 1 | 1 |
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Both the begin and end characters are defined in the Message enum in [commands.h](../../quad/src/commands/commands.h). Message types
are defined within the MessageTypeID enum in [commands.h](../../quad/src/commands/commands.h). Message ID is managed within the backend
[backend.c](../../groundStation/src/backend/backend.c) and is just a counter that is used in client_recv to number packets. Data length
varies with the command that is being sent, but the length of a command is constant. The data is sent in a specific format set by commands.
Lastly, checksum is computed within [packet.c](../../groundStation/src/backend/packet.c).
All packets sent within the system are commands, defined by the MessageTypeID enum referenced earlier, or a VPRN packet. Much of the time when
flying autonomously the commands that the user is responsible for are the getparam and setparam packets that are used to set waypoints or change
values within the computation graph, see [control_algorithm.c](../../quad/src/quad_app/control_algorithm.c) for the PID blocks.
## Adding a new packet ##
//TODO - Matt
## Data Format ##
For all commands other than the message bundle packet there is a defined length and format for sending and receiving packets. Many of the formats
will be discussed below. These packet formats are referenced from [callbacks.c](../../quad/src/quad_app/callbacks.c).
**Note:** this document may get out of date, [callbacks.c](../../quad/src/quad_app/callbacks.c) should have all the up to data packet formats.
### setparam ###
** Sent from Ground Station **
| data index | 0 - 1 | 2 - 3 | 4 - 7 |
|:----------:|:-----------:|:-----------:|:-----------:|
| parameter | node ID | node parmID | param val |
| bytes | 2 | 2 | 4 |
Does not send any response.
### getparam and getoutput ###
** Sent from Ground Station **
| data index | 0 - 1 | 2 - 3 |
|:-----------:|:-------------:|:-----------:|
| parameter | node ID | node parmID |
| bytes | 2 | 2 |
** Response to Ground Station **
The response will be of type RESPPARAM_ID.
| data index | 0 - 1 | 2 - 3 | 4 - 7 |
|:-----------:|:------------:|:-----------:|:-----------:|
| parameter | node ID | node parmID | param val |
| bytes | 2 | 2 | 4 |
### setsource ###
** Sent from Ground Station **
| data index | 0 - 1 | 2 - 3 | 4 - 5 | 6 - 7 |
|:----------:|:------------:|:-------------:|:-----------:|:-------------:|
| parameter | dest node ID | dest input ID | src node ID | src output ID |
| bytes | 2 | 2 | 2 | 2 |
Does not send any response.
### getsource ###
** Sent from Ground Station **
| data index | 0 - 1 | 2 - 3 |
|:-----------:|:-------------:|:-----------:|
| parameter | node ID | node parmID |
| bytes | 2 | 2 |
** Response to Ground Station **
The response will be of type RESPSOURCE_ID.
| data index | 0 - 1 | 2 - 3 | 4 - 5 | 6 - 7 |
|:----------:|:------------:|:-------------:|:-----------:|:-------------:|
| parameter | dest node ID | dest input ID | src node ID | src output ID |
| bytes | 2 | 2 | 2 | 2 |
### getnodes ###
** Sent from Ground Station **
//TODO - Does not list in callbacks.c, does this exist?
** Response to Ground Station **
| data index | 0 - 2*N-1 | 2*N - 4*N-1 | 4*N - (< 4096) |
|:-----------:|:------------:|:--------------:|:---------------:|
| parameter | Node IDs | Node type Is | Node names |
| bytes | 2*N | 2*N | < 4096 |
### addnode ###
** Sent from Ground Station **
| data index | 0 - 1 | 2 + |
|:-----------:|:------------:|:-------------:|
| parameter | type ID | New node name |
| bytes | 2 | var |
** Response to Ground Station **
| data index | 0 - 1 |
|:-----------:|:------------:|
| parameter | node ID |
| bytes | 2 |