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All the interface logic will be isolated in a class called USBInterface/UARTInterface. The class is described below.

USBInterface/UARTInterface

+read(endpointId): Issues a read command in either serial (UART) or pyusb (USB). EndpointId can be the specific serial port to use or the usb endpoint to be used.

+write(endpointId, data): Issues a write command in either serial or pyusb. Data parameter should be a buffer.

+create_endpoint_FC(): Returns a new endpoint, either a Serial object (UART) or Endpoint object (USB), that points to our flightcontroller.

-endpoints:

Array of dicts

Dictionary {endpointId: endpoint object (Serial object or Endpoint object)}. The first one is populated by calling the create_endpoint_FC() function in the constructor.

TODO: Data logic in FltConn module

Perform any data processing required to turn the return of read(…) or write(…) into the appropriate python object. Implemented as a set of functions in the FltConn modules. PIGOs and POGIs are constructed at this stage.

TODO: API logic in FltConn module

Exposes functionality to the worker function. Should just have get_pogi() and get_pigo() functions.

ReferenceA similar version of this will be used for the XBee Interface. This will not use the CommsInterface base class.

XBee Interface

+read_callback(): Sets up a callback that is executed when a message is recieved. self.function_dict is a dictionary of functions which are called when a message is receieved. When you get a message, decode it then call self.functionDict[device_id](data).

+write(deviceId, data): Issues a send command to that device_id

+create_device(read_function, device_port): This function should perform steps 2-3 from the tutorial, then call use add_data_recieved_callback, like in this tutorial to register read_callback as the callback function, then store the created xbee device in a dictionary with the ID as the key, {0: device, …}. Then it should set self.functionDict[device_id] = read_function. Return ID.

-device_dict: Dictionary {device_id: device object}. The first one is populated by calling the create_endpoint in the constructor.

-function_dict: Dictionary{device_id: function}, a dictionary of functions that the read callback can call once it receives a message, mapped by device_id. The default will just be {'main': main_read(…)} where main_read is whatever function is used in the GroundConnRecieve module.

Schema

To ensure ease of communication, we’ll define a specific schema for messages being sent out from the jetson as a request and messages being received by the jetson as a response. Therefore, any call to FltConnSend or GroundSend or FltConnReceive or FltConnSend will follow this schema.

Request/Response Schema (General):

Code Block

language	json

{
  "type": “QR_COORDINATES” | “QR_INFO”| “TARGET_COORDINATES” | "STATE_INFO", // Limited to a specific list of types
  "data": {...} // Dictionary whose schema depends on request type
}

Valid Types:

Request: “QR_COORDINATES”, “QR_INFO”, “TARGET_COORDINATES”
Response: “STATE_INFO”

Schemas by type

Schema for QR_COORDINATES, TARGET_COORDINATES and STATE_INFO are based off encodings with flight controller found here. Schema for QR_Info is also defined in CONOPS for 2021-2022.

Code Block

language	json

// QR_COORDINATES and TARGET_COORDINATES
{
  lattitude: double,
  longtitude: double
}

// QR_INFO
{
  info: string, // Encompasses the second line of the QR scan result
  date: string,
  time: string,
  device_id: string,
  sensor_id: string
}

//STATE_INFO
{
  lattitude: double,
  longtitude: double,
  altitude: double,
  yaw: double,
  pitch: double,
  roll: double
}

Reference

Exchanged Data

USB Protocol Overview

PyUSB implementation overview (see here for what the Endpoint object is etc.)

Jetson Nano UART overview

https://pyserial.readthedocs.io/en/latest/pyserial.html#overview

XBee Python

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