USB-CDC Speed Test

You can watch a video of this in action here.

ESP32-S3 USB serial experiments and host-side tests:

• Echo firmware (Arduino): uppercase-echo any received bytes via USB-CDC
• Echo firmware (ESP-IDF): uppercase-echo using usb_serial_jtag
• Bandwidth TX firmware (Arduino): stream 4 MiB payload over USB-CDC on BOOT press
• Bandwidth TX firmware (ESP-IDF): stream 4 MiB payload via TinyUSB CDC ACM on BOOT press
• Python echo test: iterate common host baud rates and verify echo
• Python throughput receiver: receive payload, verify CRC32, report throughput

Prerequisites

• PlatformIO (VS Code extension or pio CLI)
• uv for Python package/runtime management (curl -LsSf https://astral.sh/uv/install.sh | sh)
• Python 3.10+

Echo firmware (Arduino)

Folder: echo-firmware-arduino/ targeting esp32-s3-devkitc-1 with Arduino USB-CDC enabled.

Build and upload:

cd echo-firmware-arduino
pio run -t upload

Behavior: configures Serial at 115200; echoes incoming bytes back in uppercase.

Echo firmware (ESP-IDF)

Folder: echo-firmware-idf/ using the ESP-IDF usb_serial_jtag driver.

Build and upload:

cd echo-firmware-idf
pio run -t upload

Behavior: prints a ready line and uppercase-echoes any incoming data.

Bandwidth TX firmware (Arduino)

Folder: bandwidth-tx-firmware-arduino/.

Sends a 4 MiB payload when the BOOT button (GPIO0) is pressed.

Data format:

• 4 bytes magic: TXT1
• 4 bytes little-endian payload length
• payload bytes (repeating 0..255 pattern)
• 4 bytes little-endian CRC32 (IEEE/ZIP, poly 0xEDB88320)

Build and upload:

cd bandwidth-tx-firmware-arduino
pio run -t upload

Press BOOT once to start a transfer.

Bandwidth TX firmware (ESP-IDF)

Folder: bandwidth-tx-firmware-idf/ using TinyUSB CDC ACM.

Build and upload:

cd bandwidth-tx-firmware-idf
pio run -t upload

Device prints a ready message. Press BOOT to start a 4 MiB transfer with the same header/payload/CRC format as above.

Python echo test

Path: test-scripts/echo_baud_test.py. Dependencies are declared in test-scripts/pyproject.toml and will be resolved automatically by uv.

Run (auto-detects an Espressif device when possible):

cd test-scripts
uv run echo_baud_test.py

Specify a port explicitly if auto-detection fails (macOS example):

uv run echo_baud_test.py --port /dev/cu.usbmodemXXXX

Customize the message or baud rates:

uv run echo_baud_test.py --message "hello world\n" --baud-rates 9600 115200 230400 460800 921600

Notes:

• The device echoes bytes in uppercase; the script compares case-insensitively by uppercasing both sent/received data.
• Exit code is non-zero if any baud rate fails the echo check.

Python throughput receive test

Path: test-scripts/throughput_read_test.py.

Receive and measure the transfer from either TX firmware (auto-detects port when possible):

cd test-scripts
uv run throughput_read_test.py

Explicit port:

uv run throughput_read_test.py --port /dev/cu.usbmodemXXXX

Options:

• --baud: host setting (CDC ignores it), default 115200
• --timeout: overall timeout for a single transfer (seconds), default 60

Example output:

Received 4194304 bytes in 0.832s => 40.32 Mbit/s

Serial port auto-detection

Both scripts prefer devices with USB VID 0x303A (Espressif). If none are found, they fall back to common /dev/cu.* or /dev/tty.* candidates. You can always override with --port.