boards
https://arduino.esp8266.com/stable/package_esp8266com_index.json
megaTinyCore - megaTinyAVR https://mcudude.github.io/MegaCoreX/package_MCUdude_MegaCoreX_index.json https://github.com/MCUdude/MegaCoreX
https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
http://drazzy.com/package_drazzy.com_index.json https://github.com/SpenceKonde/megaTinyCore
https://github.com/SpenceKonde/ATTinyCore
https://nulllab.coding.net/p/lgt/d/nulllab_lgt_arduino/git/raw/master/package_nulllab_boards_index_zh.json
https://cdn.jsdelivr.net/gh/nulllaborg/arduino_nulllab/package_nulllab_boards_index_zh.json
include
use include “test.h” to add variables
snippet
// Periodically blink the onboard LED while listening for serial commands
if ((int)(millis()/500) > lastPeriod)
{
lastPeriod++;
pinMode(LED, OUTPUT);
digitalWrite(LED, lastPeriod%2);
}