This is a very minimal ESP32 program, inspired by nosdk8266. It is pure C with no SDK parts left apart from one function declaration. Also see the related esp8266-minimal project.
Code size on my version of the ESP32 toolchain (GCC 5.2.0):
| configuration | text | data | bss |
|---|---|---|---|
| UART enabled | 330 bytes | 0 | 0 |
| UART disabled | 267 bytes | 0 | 0 |
| only timer + LED | 211 bytes | 0 | 0 |
You could trim this down even further with a delay loop instead of using a timer.
Simply run:
make flash
I recommend picocom to see the serial output:
picocom --baud 115200 /dev/ttyUSB0
To understand how the ESP32 works, outside of the ESP-IDF. This was my first step towards porting the ESP32 to TinyGo. It may be useful to other people who would like to avoid the ESP-IDF, for reasons such as code size, compilation speed, or porting a new language.
Also see the esp8266-minimal project, which is very similar but for the ESP8266.
Two files include code derived from ESP-IDF. These are esp32.h (register
names) and esp32.ld (libgcc function definitions). Because they describe an
API and not an implementation I belive they cannot be copyrighted or at least
fall under fair use, but I'm not sure so use your own judgment on that. If they
are copyrightable, they are under the Apache 2.0 license.
All other files can be considered public domain, which means you can use them however you wish. If you want a bit more detail, you could consider them to be licensed under the Unlicense.