Telemetry — USB example (→ Serial Plotter web app)

Streams synthetic float channels from an ESP32-S3 to the browser Serial Plotter web app over USB, using espp::Telemetry (a binary telemetry emitter carried on the stream_frame framing, dispatcher module 3 by default).

The hosted app — https://esp-cpp.github.io/espp/apps/telemetry.html — connects on the vendor (WebUSB) interface, reads the channel schema, and plots the live sample stream. It is the binary, higher-rate, device-timestamped counterpart to the app’s text/CSV Web Serial transport.

What it does

  • Declares four channels — sine, cosine, noise, ramp — as the schema.

  • A producer task emits one sample (a float per channel) every ~10 ms (100 Hz), timestamped with the device clock.

  • Exposes the stream over the USB vendor (WebUSB) interface; a Dispatcher routes the emitter’s module (Telemetry::Config::module, 3 by default; only a routing key, the hosted Serial Plotter finds it through discovery by its protocol id) to it and serves capability discovery so the browser Device Hub lists this device and links to telemetry.html.

  • The web app can pause/resume the stream and request a rate (SET_STREAM), and requests the schema on connect (GET_SCHEMA).

espp::Telemetry itself is transport-agnostic (the stream_frame framing works over CDC / UART / a socket too); this example streams over WebUSB because that is what the web app’s binary path consumes.

Swap the synthetic generator for your real signals: build a std::array<float, N> in channel order and call telemetry.emit(...).

Build & run

idf.py -p /dev/ttyACM0 flash          # target esp32s3 (set in sdkconfig.defaults)
idf.py -p /dev/ttyUSB0 monitor        # console is on UART0 (USB-UART adapter)

Then open the Serial Plotter web app, click Connect (USB), and pick the “espp Serial Plotter” device. The system console/logs go to UART0: on the S3 / P4, USB-Serial-JTAG shares the native USB port’s PHY with USB-OTG, which TinyUSB takes over.

Standard USB services

Like every espp USB example, this one serves the standard service set on its framed USB link(s) next to its own protocol, so the hosted consoles and the Device Hub (which finds each service through discovery, by protocol id) work against it:

Service

Module (default)

Protocol id

Console

espp::SystemService – device info, reboot, reboot into the bootloader

7

espp.system

system console

espp::MonitorService – heap regions + task table, on request or streamed

8

espp.monitor

system console

espp::OtaService – firmware update (host-driven rollback confirmation)

0

espp.ota

OTA console

espp::CoreDumpService – last-crash report, core dump download / erase

4

espp.coredump

coredump console

partitions.csv therefore carries the OTA layout (otadata, ota_0, ota_1) plus a coredump partition, and sdkconfig.defaults enables core dumps to flash, OTA rollback and the FreeRTOS run-time statistics the task monitor reads. Every device->host write on a transport goes through one mutex, so the services (and any streaming) never interleave frames.

Notes

  • Native USB (vendor / WebUSB) needs an ESP32-S3 (also S2 / P4) — not the classic ESP32. sdkconfig.defaults pins esp32s3 and enables the TinyUSB vendor class.

  • WebUSB / Web Serial are Chromium-only and need a secure context (https, http://localhost, or file://).