Messages Format

Introduction

Messages Format and how to use them

For the message definitions see http://docs.paparazziuav.org/latest/paparazzi_messages.html

Types

Paparazzi "PPRZ" standard message for direct serial connection

Pprzlink v1.0

PPRZ-message: ABCxxxxxxxDE
byte:    |   value:
    0        PPRZ_STX (0x99)
    1        LENGTH (PPRZ_STX->PPRZ_CHECKSUM_B)
    2        SENDER_ID
    3        MSG_ID
    4..(N-2) MSG_PAYLOAD (messages.xml)
    N-1      PPRZ_CHECKSUM_A (sum[B->C])
    N        PPRZ_CHECKSUM_B (sum[ck_a])

Pprzlink v2.0

Note that there is currently no explicit way to recognize whether the protocol is v1.0 or 2.0 so it has to be known before the communication.

PPRZ-message: ABCxxxxxxxDE
    A PPRZ_STX (0x99)
    B LENGTH (A->E)
    C PPRZ_DATA
      0 SOURCE (~sender_ID)
      1 DESTINATION (can be a broadcast ID)
      2 CLASS/COMPONENT
        bits 0-3: 16 class ID available
        bits 4-7: 16 component ID available
      3 MSG_ID
      4 MSG_PAYLOAD
      . DATA (messages.xml)
    D PPRZ_CHECKSUM_A (sum[B->C])
    E PPRZ_CHECKSUM_B (sum[ck_a])

Secure Paparazzi (S-PPRZ) for serial and transparent modem communication

The overhead is 16 bytes (4 bytes of counter, 16 bytes of tag), plus the necessary key exchange at the beginning of communication.

S-Pprzlink v1.0

PPRZ-message: ABCxxxxxxxDE
byte:      |     value:
   0             PPRZ_STX (0x99)
   1             LENGTH (PPRZ_STX->PPRZ_CHECKSUM_B)
   2-5           COUNTER (4 bytes)
   6             encrypted SENDER_ID
   7             encrypted MSG_ID
   8..(N-16)     encrypted MSG_PAYLOAD (messages.xml)
   (N-15)..(N-2) TAG (16 bytes)
   N-1           PPRZ_CHECKSUM_A (sum[B->C])
   N             PPRZ_CHECKSUM_B (sum[ck_a])

S-Pprzlink v1.0

byte	Value	Type
0	PPRZ_STX (0x99)	Header
1	length N (PPRZ_STX->checksum B)	Header
2	counter LSB 1	Authenticated data
3	counter LSB 2	Authenticated data
4	counter LSB 3	Authenticated data
5	counter LSB 4	Authenticated data
6	sender ID	Encrypted payload
7	message ID	Encrypted payload
8..(N-16)	(optional) message payload (0-234 bytes)	Encrypted payload
(N-15)..(N-2)	tag (16 bytes)	Authentication tag
N-1	checksum A	Header
N	checksum B	Header

S-Pprzlink v2.0

In this case we decrypt only packets with matching DESTINATION (or broadcast), to avoid decrypting unwanted data.

PPRZ-message: ABCxxxxxxxDE
    A PPRZ_STX (0x99)
    B LENGTH (A->E)
    C PPRZ_DATA
      0 SOURCE (~sender_ID)
      1 DESTINATION (can be a broadcast ID)
      2-5 COUNTER (4 bytes)
      // ciphertext start
      6 CLASS/COMPONENT
        bits 0-3: 16 class ID available
        bits 4-7: 16 component ID available
      7 MSG_ID
      8 MSG_PAYLOAD
      . DATA (messages.xml)
      // ciphertext end
      8-19 TAG (12 bytes)
    D PPRZ_CHECKSUM_A (sum[B->C])
    E PPRZ_CHECKSUM_B (sum[ck_a])

XBee API format

XBee-message: ABCDxxxxxxxE
    A XBEE_START (0x7E)
    B LENGTH_MSB (D->D)
    C LENGTH_LSB
    D XBEE_PAYLOAD
      0 XBEE_TX16 (0x01) / XBEE_RX16 (0x81)
      1 FRAME_ID (0)     / SRC_ID_MSB
      2 DEST_ID_MSB      / SRC_ID_LSB
      3 DEST_ID_LSB      / XBEE_RSSI
      4 TX16_OPTIONS (0) / RX16_OPTIONS
      5 PPRZ_DATA
        0 SENDER_ID
        1 MSG_ID
        2 MSG_PAYLOAD
        . DATA (messages.xml)
    E XBEE_CHECKSUM (sum[D->D])

   ID is AC_ID for aircraft, 0x100 for ground station

Telemetry storage format for data logger

TLM-message: ABCDEFGHxxxxxxxI
    A PPRZ_STX (0x99)
    B LENGTH (H->H)
    C SOURCE (0=uart0, 1=uart1, 2=i2c0, ...)
    D TIMESTAMP_LSB (100 microsecond raster)
    E TIMESTAMP
    F TIMESTAMP
    G TIMESTAMP_MSB
    H PPRZ_DATA
      0 SENDER_ID
      1 MSG_ID
      2 MSG_PAYLOAD
      . DATA (messages.xml)
    I CHECKSUM (sum[B->H])