Explore SoftwareSerial and using Arduino Uno as a proxy for ATtiny85

.gitignore

.pio/
include/
lib/
src/
test/

main.cpp

// https://www.arduino.cc/en/Tutorial/LibraryExamples/SoftwareSerialExample
/*
  Software serial multple serial test

 Receives from the hardware serial, sends to software serial.
 Receives from software serial, sends to hardware serial.

 The circuit:
 * RX is digital pin 2 (connect to TX of other device)
 * TX is digital pin 3 (connect to RX of other device)

 Note:
 Not all pins on the Mega and Mega 2560 support change interrupts,
 so only the following can be used for RX:
 10, 11, 12, 13, 50, 51, 52, 53, 62, 63, 64, 65, 66, 67, 68, 69

 Not all pins on the Leonardo support change interrupts,
 so only the following can be used for RX:
 8, 9, 10, 11, 14 (MISO), 15 (SCK), 16 (MOSI).

 created back in the mists of time
 modified 25 May 2012
 by Tom Igoe
 based on Mikal Hart's example

 This example code is in the public domain.

 */
#include <Arduino.h>
#include <SoftwareSerial.h>

SoftwareSerial mySerial(PB1, PB2); // RX, TX

void setup()
{
  // set the data rate for the SoftwareSerial port
  mySerial.begin(9600);
}

void loop() // run over and over
{
  mySerial.print("Hello world!");
  // digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  // mySerial.print("Hello world!");
  // digitalWrite(LED_BUILTIN, LOW);
  // delay(1000);
}

platformio.ini

; PlatformIO Project Configuration File
;
;   Build options: build flags, source filter
;   Upload options: custom upload port, speed and extra flags
;   Library options: dependencies, extra library storages
;   Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html
[platformio]
default_envs = attiny85

[env:attiny85]
platform = atmelavr
board = attiny85
framework = arduino

; Default fuses
; avrdude: safemode: Fuses OK (E:FF, H:DF, L:62)
; https://docs.platformio.org/en/latest/platforms/atmelavr.html#fuses-programming
; To update, run: platformio run -t fuses
; Default
; board_fuses.efuse = 0b11111111
; board_fuses.hfuse = 0b11011111
; board_fuses.lfuse = 0b01100010
board_fuses.efuse = 0b11111111
board_fuses.hfuse = 0b11011111
board_fuses.lfuse = 0b11100010 ; CKDIV8 disabled (now delay is same as an out of the box Arduino)

; Set same timing across boards (not quite perfectly in sync, likely RC issues but close enough)
board_build.f_cpu = 8000000L ; 8MHz

[env:arduino_uno]
platform = atmelavr
board = uno
framework = arduino

; Set same timing across boards (not quite perfectly in sync, likely RC issues but close enough)
board_build.f_cpu = 8000000L ; 8MHz