ESP32 Serial Demo

Demo of serial protocols for use in evaluating oscilloscope serial decoders.

Protocols supported:

• I2C
• SPI
• UART

Setup

Minimal setup is required to use with a scope. With the exception of I2C, no wiring is required. Flash a dev board using ESP-IDF or PlatoformIO and attach scope probes to the GPIO pins as documented below.

Optionally connect GPIO 4 to GPIO 6 (I2C SCA) and GPIO 5 to GPIO 7 (I2C SCK) if you want to observe the controller sending data to a simulated peripheral. If this isn't done, you will only able to observe the controller initiating a write to the device's address, but it won't transmit the payload.

Signals

Payload:

All of the protocols write a raw 16bit integer followed by series of bytes from 0x00 to 0x40. The integer is incremented with every packet. Note: the integer is sent little endian, so you will see the first byte rapidly moving from 0x00 to 0xFF, and then the second byte increments. You can use this to play with triggering on the data of the first byte.

I2C

The controller writes the payload described above on SCA. The peripheral does not respond other than the I2C ack.

Pins

• SCA: GPIO 4
• SCL: GPIO 5

Signal parameters

• Clock frequency: 100KHz
• I2C address: 0x28
• Delay between packets: 10ms

SPI

The controller writes the payload described above on MOSI. The peripheral does not respond.

Pins:

• CS: GPIO 9
• CLK: GPIO 10
• MISO: GPIO 11
• MOSI: GPIO 12

Signal parameters:

• Clock frequency: 10MHz
• Delay between packets: 10ms

UART

The controller writes the payload described above on TX. The peripheral does not respond.

Pins:

• TX: GPIO 17
• RX: GPIO 16

Signal parameters:

• Baud rate: 115200
• Data bits: 8
• Parity: None
• Stop bits: 1
• Delay between packets: 1000ms

Compiling

ESP-IDF

Set the target and build.

# only need to set the target once
idf.py idf.py set-target esp32s3

idf.py build
idf.py flash -p <path to your device>

PlatformIO

pio run -t upload

Misc Notes

The main uart is initialized to 115200 8/N/1 and prints the GPIO and speed settings on startup for easy reference.

I developed this on an ESP32S3, but it should be easily portable to any other ESP chip and dev board. As I just whipped this together to evaluate a new scope, the pins and clock speeds are not configurable other than in the source files directly. Maybe one day I'll add user input and turn it into a real scope demo board.

If you are a nix user, there is a flake.nix and .envrc that will install the version of esp-idf and platformio I used during development.

The payload is lengthy in order to test signal decoding of packets that don't fully fit on the screen of the scope. Annoyingly, there are some scopes that will only decode from what's currently shown on the screen despite having the full packet in memory.