DROS Message Format Maintained by: David Austin

• 1.0 Introduction
• 2.0 Message Management
• 3.0 Message Template
• 4.0 Message Formats
• 4.1 General Messages

1.0 Introduction

For communication, a standard is required which both parties know. In the context of a software system with components that must communicate with each other, this means that, at the lowest level, there must be a standard for the bytes that are actually transmitted. This document outlines the template of the messages (in terms of bytes) and also describes how messages should be managed.

Note: you do not have to use GeneralComms: it is possible to communicate with any process within DROS using whatever communications library you wish, so long as you obey this message formatting protocol.

2.0 Message Management

The management of message formats over time is a crucial issue. DROS will exist for a period of years, meaning that we must think carefully about how new message formats are created, how they can be changed and finally, how obsolete message formats can be deleted. Thinking about this subject, I've decided on the following rules:

1. New message formats can be created as and when required. [The number of possible formats is large and can be made larger.]
2. Existing message formats cannot be altered. [If you change a message format that has been released, you will break someone else's system. Instead, create a new message and mark the old one as obsolete and begin phasing it out (over a fairly long period!).]
3. Obsolete message formats can be deleted after a period of not being used in the DROS code base. [I'd suggest 6 months. When a message is obsolete, note this and the date in GlobalHeaders/DROSMessages.h. ]

Note that every message should be replied to (I believe) and that the Id field from the original message should be copied to the response. A good idea would be for the Id to be a sequence number so that the client can have a lot of outstanding requests.

4.0 Message Formats

The message formats are listed here. However, for up to date information, check the file GlobalHeaders/DROSMessages.h.

General Messages

Invalid

This message has no data (aside from the header).

ConnectionlessPacket

Ack

GenString

Copyright 2001 David Austin