No idea why the ESP32-C3 needed to be written starting at 0x0, rather than 0x1000, but sure enough it did. I couldn't figure out why nothing could seem to be written successfully to my STAMP-C3, but basically nothing was working. Now, thanks to a blog post I found, it's successfully running the generic ESP32-C3 MicroPython binary.

Successful esptool.py commands:

esptool.py -p COMx -b 1500000 --before default_reset erase_flash
esptool.py -p COMx -b 1500000 --before default_reset write_flash -z 0x0 esp32c3-20210902-v1.17.bin

Result on REPL:

ESP-ROM:esp32c3-api1-20210207
Build:Feb 7 2021
rst:0x1 (POWERON),boot:0xc (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fcd6100,len:0x121c
load:0x403ce000,len:0x744
load:0x403d0000,len:0x26c4
entry 0x403ce000
MicroPython v1.17 on 2021-09-02; ESP32C3 module with ESP32C3
Type "help()" for more information.

@didier9 said in M5Stamp C3 - I2C interface:

Now I just have to find out how to configure and access it from the Arduino IDE :)

Good luck! I've had a dilly of a time trying to consistently get something (useful!) loaded to the device. Generic Micropython for ESP32 doesn't work, the generic Micropython builds for the ESP32-C3 don't work, not does building the package from scratch and loading it. I thought perhaps it was faulty, but I did get the below sketch to load and run, giving me functional serial output...so I know it's not dead, but I'm glad I bought multiple devices.

Examples for STAMP-C3 -> ESP32 -> ChipID -> GetChipID

FYI, on the STAMP-PICO, I used the below in Arduino to run I2C on the Grove port, to talk with an adapter cable to Adafruit StemmaQT sensors. Obviously it doesn't DO anything, but it's what was required to use specific pins for I2C.

#include <Wire.h>
// Declare alternate I2C pins
#define I2C_SDA 32
#define I2C_SCL 33
void setup(void) {

// Initialize I2C using alternate pins

I2CMS.begin(I2C_SDA, I2C_SCL, 400000);
}