Saturday, 16 February 2019

ESP-Now BATMAN data encapsulation

I've been working on other stuff recently but haven't totally forgotten my mesh network library.

Over the last couple of days I've been fiddling around with encapsulating data in a way that's very easy for somebody writing an Arduino sketch.

The first third of this is done in that I've written a set of overloaded functions for the common Arduino data types including both char arrays and the much maligned String type.

There's a single function 'add' that starts building a packet for you and works out how to pack the data based off the type of the single argument.

To add some data then send it (flooding the network) it's just a few lines of code.

mesh.add(value1);
mesh.add(value2);
mesh.add(value3);
mesh.add(value4);
mesh.add(value5);
mesh.add(value6);
mesh.send();

Both functions return true or false depending on whether they are successful. You can add as many values as will fit in an ESP-Now packet and if there's no space left, 'add' returns false.

I've written a small sketch to send random amounts of random data of random types every ten seconds. It can fit about 30 values in each packet depending on exactly which types are involved.

This has been running for about eighteen hours without any hiccups so I'm happy with it.

My next task is to write a set of functions to give access to this data from a sketch when it arrives. I've written the logic to decode packets and print out the contents nicely but need to think through how to present it to a person writing their own code with the library.

It's not as easy as the 'add' function as I can't really overload it, unless I do something like make people send pointers to their variable. Which I don't think is very friendly, however efficient it might be.

There's also the matter of sending messages to specific nodes, which means a whole load more public functions to find out about the mesh and allow the retrieval of MAC addresses. Which again feels unfriendly because you're going to end up with hard coded MAC addresses unless somebody layers on their own way of mapping MAC addresses to their various nodes' identities or functions.

I might implement my idea of giving nodes names which are simple text strings. Who cares what the MAC address is after all, it's what code is running that matters.

So you could call one node 'Daylight sensor' and another 'Light switch' and the former tells the latter to switch on when it gets dark. I'm not expecting this library to be used for IoT type things like this but I think it's a good example of why having human readable names is desirable. I could just add the name to the 'status' protocol packets I already send.

It's slow discovery of requirements as I write that demonstrate why this isn't a professional piece of software engineering and also why it's taking me so long. :-)

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