ESP-Now BATMAN/NHS progress

I'm still wrestling with making what I hope will be a fully featured mesh protocol for battery powered ESP8266 devices.

Having put in the main building blocks of ELP and OGM from BATMAN IV I wanted to add something of my own to monitor the 'health' of the devices. I've coined the term Node Health Status (NHS) for these packets. Because British.

This is relatively simple just now, it periodically sends uptime, free heap memory, starting heap memory, supply voltage, number of peers and radio transmission power to all its neighbours. Nodes store this and make it persistently available.

My reasoning for doing this is it will allow me to 'visualise' the network more accurately without having direct access to each node and certain features need an election process to decide which nodes to run on.

The first use I'll have for this is that nodes with fewer peers will run as a SoftAp to help discovery of new nodes. I'm hoping having fewer peers is a passable heuristic for being somewhere 'sparse' on the network.

Monitoring of supply voltage and uptime give simple measures of battery health and if a node has rebooted. Heap monitoring is something that may feed into feature elections.

I also spent a fair bit of time playing with management of transmission power. So long as it is not experiencing consequential packet loss each node lowers power until packet loss starts. Then it raises power and sets a 'floor' it will not go below. Periodically it lowers the floor slightly to see if power can go down further, but will immediately raise it again if packet loss starts. If we had an easily accessible RSSI measure for ESP-Now peers this wouldn't be necessary but the only RSSI information exposed to us in the standard libraries is the RSSI for an AP association.

It might be possible to infer from transmission power, number of peers and so on whether a node actually has to act as a router or not, switching that off/on to conserve resource. However that's probably out of scope for now and is making a big change to the BATMAN IV routing algorithm that would have big unintended consequences.

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