The front end built for the PROTOS miniHIL, a small hardware-in-the-loop test rig. It is a React (Next.js) app that lets you watch a test run on the hardware as it happens: live logs, signal traces and execution state, all streamed from the device while the test executes. The harder problem behind the views was the data path and performance. A test run produces a lot of data on an MCU. Additionally, the goal was to allow the user to open multiple browser windows showing different aspects of the test run.
The data comes off the miniHIL hardware itself, an STM32-based MCU system that runs the test cases in real time. The hardware is connected to the PC via USB (1.1 full speed device). A Java backend on the PC owns that USB link, deserializes the low-level protocols, and exposes the result to the GUI over a WebSocket. Inside the browser a single shared worker holds the websocket connection and fans the decoded stream out to every open window.