First prototype:

Git and documentation

The first prototype of the tokenbus is documented here: https://github.com/autotel/TokenBusHomogeneousNetwork

Media

Testing the speed of the prototyped network

Integrated prototype 1

The integrated prototype is developed in the branch COM_common_bus on the js-virtualModular git repository. It is based on the previous work, with some modifications

To reduce the amount of bytes to be transmitted, I decided to tweak the communication protocol from the one used in the JavaScript based prototype here

Bus communication syntax

the messages for the bus will be defined as follows: (each byte is separated by a comma)

msg mode | length , origin | destination [, payload]

the name of each byte is:

header byte, routing byte, payload …

In any given module, the first two bytes will define whether this message must be ignored or taken. It is also possible that the first byte indicates whether the message should be ignored.

Header byte:

modes:

ignore: message must be ignored
com: messages whose role is to establish or modify lower level parameters of the communication protocol (such as requesting id’s resetting the network, etc.)
payload, destination-targeted: the message is targeted to one specific module
payload, source-targeted: the message is targeted to every module that has the source module registered as input
payload, global-targeted: the message is targeted to every module in the network.
payload, link: register the origin module in the target module’s output list

length:

the header is shifted a nibble, and or’ed with the length (0-16). The length is inclusive of header and routing bytes. The message length format has not been defined, it can be:

number of bytes
number of words
2 exponential to the number of bytes (1,2,4,8,16 …, 32768)

Also, there is the option of using the F length as undefined length, in which case some number should be defined as terminator bytes, most likely an ASCII CR character. In such case, an escaping protocol should be deviced.

[https://en.wikipedia.org/wiki/ASCII]

Routing byte

Routing byte is only used for payload messages, since the com messages will have a different syntax. This byte results from (emitter_id)<<4 | (destination_id). Emitter id is the emitting module’s id within the current network. The destination and source bytes define whether to ignore the incoming payload, according to the indicated mode of message.

The bus network used in other network configurations

it is possible that in the future, with access to more complete micro-controllers or development tools, the connections between modules become physical (using mechanical connectors between modules) instead of virtual (where modules chose their targeted messages according to id’s in a bus). It is also possible that these modules may form more than one bus, to allow faster communications in a network that has many modules. There are reasons, however untested, that may lead to think that this protocol can be applied to such cases.

A device may define one connector as input, and the other connector as output. An example where there is a node that outputs to another node would form a parent-child network, in which the parent is constantly sending information to the child while passing the token to receive “upstream” information from the child.
- In this case, the routing bytes would become redundant. However, it could be integrated into the protocol that when a network has only two nodes, only global messages will be sent without routing bytes.

Many devices could be connected as parents of a device, whose roles would be defined by which connector is being used for this communication. The parent-child role is defined at a higher level of abstraction, since the communication is all-to-all, in all cases.
If the connection is node to node, most of the protocol can be stripped away by having the parent retain the send token constantly, and keeping the child in a constant listening mode. These modules could also be integrated in a token bus as far as the modules can detect being connected to a bus, and change their behaviour accordingly.

[The Complete MIDI 1.0 Detailed Specification]

Autotel

token bus design