PSAS Packet Serializer¶

Message¶

A PSAS Message has a header with an ASCII four character code (e.g., ‘ADIS’) that identifies it. This is followed by a 6 byte timestamp in nanoseconds. This is always nanosecond since beginning of a program, which is usually the same as boot time for a device. This is followed by two bytes that give the size of the rest of the message. The remainder of the message is a collection of Data.

Data¶

Data can be almost anything, even other messages. Usually it’s a pre-defined set of fixed sized numbers

A Message with a header and pre-defined container

ADIS¶

ADIS16405

Format Description:

BMP1¶

Pressue

Format Description:

FCFH¶

FCFHealth

Format Description:

GPS1¶

GPSFix

Format Description:

GPS2¶

GPSFixQuality

Format Description:

GPS80¶

GPSWAASMessage

Format Description:

GPS93¶

GPSWAASEphemeris

Format Description:

GPS94¶

GPSIonosphereUTC

Format Description:

GPS95¶

GPSEphemeris

Format Description:

GPS96¶

GPSPsudorange

Format Description:

GPS97¶

GPSProcessor

Format Description:

GPS98¶

GPSAlmanac

Format Description:

GPS99¶

GPSSatellite

Format Description:

LTCH¶

LaunchTowerComputer

Format Description:

MPL3¶

MPL3115A2

Format Description:

RNHH¶

RNHHealth

Format Description:

RNHP¶

RNHPower

Format Description:

RNHU¶

RNHUmbilical

Format Description:

ROLL¶

RollServo

Format Description:

SEQE¶

SequenceError

Format Description:

SEQN¶

SequenceNo

Format Description:

V8A8¶

Venus8Navigation

Format Description:

VSTE¶

State

Format Description:

Message Class¶

The message class can be initialized with information about the data that can be packed in it. This will make an object with encode and decode methods available for packing and unpacking.

class psas_packet.messages.Message(definition)¶

Definition of a message type

Parameters:	definition (dict) – Dictionary defining data in a message
Returns:	Message instance

Suitable metadata can be passed in and this class will perform necessary pre-compute steps and create a usable message instance for a specific data source.

decode(raw)¶

Decode a single message body (the data lines). Header info and message boundaries are solved in network

Parameters:	raw (bytestr) – Raw string of bytes the length of
Returns:	A dictionary of values in normal units

encode(data)¶

Encode a set of data into binary

Parameters:	data (dict) – A dictionary of values to encode
Returns:	Binary ecoded data

Uses the struct package to encode into byte array. The dictionary should have values who’s keys match the members list.

typedef()¶

Autogen c style typedef structs

Returns:	String c code for the data and header for this packet

Header¶

Encodes and decodes message headers

class psas_packet.messages.Head¶

Encode and decodes message headers

decode(raw)¶

Take a buffer of bytes and attempt to decode a header

Parameters:	raw (bytes[]) – byte array to decode
Returns:	tuple of the fourcc, timestamp, and lenght

encode(message_class, time)¶

Make a header for a given message class. Headers also contain timestamps of the local time a data was created.

Parameters:	message_class (Message) – Type message to encode time (int) – Timestamp in nanoseconds
Returns:	array of raw bytes the size of a Head.struct.size

Exceptions¶

class psas_packet.messages.MessageSizeError(expected, got)¶

Raised when the byte str to be unpacked does not match the expected size for this type. Check your message boundaries.

Parameters:	expected (int) – correct size got (int) – attempted size
Returns:	MessageSizeError exception

Send A Telemetry Packet¶

Open a UDP socket, and send a message of type “ADIS” to port 25000 on localhost

from psas_packet import io, messages
from contextlib import closing
import socket
import time

# Data type we're going to use
ADIS = messages.MESSAGES['ADIS']

# Data to pack
data = {
    'VCC': 5.0,
    'Gyro_X': 0.0,
    'Gyro_Y': 0,
    'Gyro_Z': 1,
    'Acc_X': -9.8,
    'Acc_Y': 0,
    'Acc_Z': 0,
    'Magn_X': 53e-6,
    'Magn_Y': 0,
    'Magn_Z': 0,
    'Temp': 20,
    'Aux_ADC': 0,
}

# Open a UDP socket
with closing(socket.socket(socket.AF_INET, socket.SOCK_DGRAM)) as sock:
    sock.bind(('', 0))
    sock.connect(('127.0.0.1', 25000))

    # Network IO class, with our socket as connection
    net = io.Network(sock)

    # send just data (no header)
    #             type, sequence no, data
    net.send_data(ADIS,           0, data)