Noisefloor Firmware

A couple of weeks ago, I started working on another of my infinite small projects.

This time, I needed a tool that could show me what was going on with another piece of firmware I was working on that was transmitting data regularly in the unlicensed 2.4 GHz frequency band.

The problem is this: I have multiple transmitters using the same frequency to send data to a single receiver. When the data rate starts to creep upward and the interval between transmissions decreases, you start getting serious resource contention.

It's a classic multi-user situation, which is solved in other wired and wireless standards using things like Carrier Sense Multiple Access / Collision Detection (CSMA/CD). (In Ethernet or Wi-Fi, example.)

I don't have access to the specialized off-the-shelf tooling needed to monitor the radio spectrum (it's pretty expensive). So I decided to build my own, very limited, very specific tool.

That tool is Noisefloor (broken link), a small tool to help me visualize and debug a Time Division Multiple Access multiplex scheme by sampling the TDMA timeslot and plotting out when the various nodes are transmitting.

It runs on Nordic Semiconductor nRF5 Series (broken link) chips using a single firmware executable.

Specifically: the nRF51422, nRF52832, and nRF52840.

That's right, there's a single binary file to load, compiled to the ARM v6-M specification, that runs on the off-the-shelf nRF51-DK, nRF52-DK, and nRF52840 Dongle development boards.

Part of the fun of developing this firmware was figuring out how to do write-once, run-anywhere code that dynamically adapts to the underlying microcontroller.

Anyways, thus far, I've pushed three posts out on the topic, and am documenting it as I go, including Requirements and Architecture specs. The code is almost feature-complete, and I'll be slowly writing that up, too.

For more info, please check out the project (broken link). Any feedback or questions would be welcome.