STC

STC (Serial Transmission Control) is a serial protocol. It was designed to establish communication between a Raspberry Pi and an Arduino Nano.
This repository contains the source of the protocol. It is implemented for Linux (#define _LINUX) and Arduino (#define _ARDUINO).

Also included is a Sniffer, which can be used to monitor the traffic.

Concept

The STC protocol sends data in form of packets (messages) similarly to how Ethernet works. To prevent data loss a packet (SYN) gets resend until a corresponding ACK packets is received (similar to TCP).

Structure

A packet can be split into three parts:

• The magic number, which is used to determine the start of a packet
• The header, which contains control field
• The body, which contains the data to be sent

Magic Number

 0                   1                   2                   3   
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Magic Number                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                                  (in bits)

• Magic Number (0xDECAFBAD): Indicates start of frame

Header

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             ID                |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              TCN                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      TCF      |      CRC      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                                  (in bits)

• ID: Indicates type of message and corresponding body
• Length: Length of body in bytes
• TCN(Transmission Control Number): Increments with each message
• TCF(Transmission Control Flags):
  • 0b00000001: SYN
  • 0b00000010: ACK
  • 0b00000100: RST
• CRC: Checksum over complete message except CRC field

Sniffer