Milan, Italy
Originally published: 20/11/2017
TSDL (Tardy Serial Data Link) v2.0 specification
Invented by Giovanni Blu Mitolo,
released into the public domain

Related implementation: /src/strategies/ThroughSerial/
Compliant versions: PJON v10.0 and following
- Frame separation provided by SFSP v1.0

TSDL v2.0

TSDL (Tardy Serial Data Link) is a simplex or half-duplex serial data link that supports both master-slave and multi-master configuration. It supports collision avoidance, reliable frame separation and optional synchronous response to frame transmissions.

 ______ TX   RX ______
|      |-------|      |
        RX   TX

TSDL can be used to establish a point-to-point link between two devices if used with a bare serial link, or supporting one or many to many communication with physical layers that are supporting this feature, like serial radio or RS485 transceivers.

Basic concepts

  • Frame separation support provided by SFSP v1.0
  • Support collision avoidance
  • Support optional 1 byte synchronous response to frame transmissions

Collision avoidance

Before a frame transmission, the serial buffer is read, if not empty ongoing communication is detected and collision avoided, if empty for a duration longer than the time-in (that should be common on all connected devices) before transmission, plus a short random time, frame transmission starts in which the packet is entirely transmitted.

Synchronous response

A frame transmission can be optionally followed by a synchronous response by its recipient.

Transmission                                    Response
 _______  ______  ______  _____                   _____
|  149  ||  H   ||  I   || 234 | LATENCY         |  6  |
|_______||______||______||_____|                 |_____|

Between frame transmission and a synchronous response there is a variable timeframe influenced by latency and CRC computation time. The maximum time dedicated to potential acknowledgement reception must be shorter than the transmission time-in (to avoid other devices to disrupt a response exchange) and it is estimated adding the maximum frame length CRC computation time to the expected latency.

This document is automatically generated from the github repository. If you have noticed an error or an inconsistency, please report it opening an issue here

The PJON protocol handbook

This is the first publication about PJON, it contains the documentation, the specification, many application examples and troubleshooting techniques. The book is made in Italy and within its 216 pages the whole PJON network protocol stack and its strategies are accurately described with graphs and color pictures. If you are interested in the PJON protocol and you would like a printed copy, pre-order an early version personally signed by Giovanni Blu Mitolo filling in the form below: