RF24Network Arduino/RPi Library - A New Development
What is RF24Network?
It is a library built upon the core RF24 driver for nrf24l01 radio modules that attempts to provide a simple interface for connecting anywhere from a few, to hundreds of wireless radio modules, connected to Arduino or Raspberry Pi devices. Uses don't need to know every detail of the radio modules in order to setup and operate a network of them. The library handles configuration, addressing, interconnections, and routing, so users can focus on creating household or long distance radio sensor networks, with data being routed automatically through the network to its intended destination.
I've been doing quite a bit of work on the core RF24 radio driver, including a wide range of changes and updates, and wanted to test out some of the more interesting features of the modules on a large scale. The existing network layer (originally by ManiacBug) provided a great foundation to begin, as it contained all of the required features of an RF24 radio network, and used a system of routing and addressing that is well suited to small devices like Arduino or ATTiny.
Some of the new features may seem unnecessary or overkill, and some will probably be, but others will support scenarios just not possible in the previous configuration. I've created a development repository and associated documentation that will be kept up roughly in accordance with development, since it will all take time to test fully, but it seems to work well and some of the features are pretty interesting.
RF24Network now supports fragmentation for all devices, including via multicasting and is enabled for all devices except ATTiny by default. The library is fairly stable at this point, and testing is ongoing with RF24Ethernet and RF24Mesh.
Fragmentation support was recently added for the RPi and Arduino Due. Standard AVR devices (Arduino Uno etc) are able to send large, fragmented payloads, but cannot yet reassemble them. See below to enable. Usage is exactly the same, but any very long payload lengths will be accepted.
Routing changes have been partially reverted to use a limited number of retries (auto-ack) where possible, and function similarly to the master branch, although network ACKs are still utilized.
Some defaults have been changed:
- Multicasting is enabled by default. This limits the number of normal child nodes/parent to 4.
- Fragmentation is totally disabled by default on AVR devices
- Uncomment defines in RF24Network_config.h to disable/enable these options
Fragmentation and reassembly support is enabled by default, with a maximum payload size of 120 bytes. Users can configure the memory buffers, or disable fragmentation by editing the config.h file. See here for the documenation. When enabled, data is sent as usual, and the network layer manages fragmenting and reassembling the data automatically.
The development version currently uses a different addressing format, using specific addressing chosen for use in radio transmission. See the datasheet and this blog post for more information. Users simply specify an octal address (01-05) as before for example, and the radio addresses will be configured accordingly.
Routing and Acknowledgement
Previously, payloads that were routed over one or more nodes were not acknowledged, so the transmitting radio had no way of knowing if payloads were delivered. *New: In the development version, users have the ability to specify whether or not the network will respond with an ACK, simply by choosing from a range of message types. Typical user message types of 65 through 127 will be acknowledged, and message types 1 through 64 will not be acknowledged. There are a few benefits to this arrangement, since network acks can automatically help to prevent nodes from flooding the network with traffic, and no-acks can be used when a response is desired from the recipient etc.
Direct Routing and Failovers
Network frames can now be logically addressed to one node, and sent to any other node for routing. This allows some dynamic topology, and can also be used to reduce routed traffic on a network. See the documentation links below for specifics and limitations.
A multicasting feature has also been added that allows, for example, the master node to send out a single network payload, and have it delivered to hundreds of network nodes very rapidly. Multicast relay nodes can be used to disperse messages throughout all or partial areas of the network. Multicasting is enabled by un-commenting #define RF24NetworkMulticast in the RF24Network_config.h file, since it requires additional program space and memory.
Performance on the network will be similar, but users will see a much higher error rate using the development version, as it gives a real indication of success or failure of payloads. Data throughput should be increased in most cases, due to reduced retry periods, and the new routing protocol.
Additional Technical Details and Information:
Documentation for the development version can be found here, and should be kept pretty consistent with changes. It contains information specific to the new routing and delivery protocols, as well as updated class documentation for usage.
The development repo is found here, and it can be downloaded here. Features and functions found to be stable and beneficial are likely to be merged into the master branch eventually. The development branch should be relatively stable at any given time, but is in no way guaranteed to be.