No installation needed – it’s part of the core.

: You can create a new serial object by specifying which digital pins will act as RX (Receive) and TX (Transmit).

Each bit timing requires precise delayMicroseconds() calls. At 115200 baud, the bit time is ~8.68 µs. The Arduino’s 16 MHz clock executes ~1 instruction per 62.5 ns, but interrupt latency (even for millis() ) can be 4–10 µs – enough to miss a bit.