Serial.flush() have a problem.

[jyzhkj]

void loop() { digitalWrite(12, 1); Serial.print("abcdffew"); Serial.flush(); digitalWrite(12, 0); delay(100); // wait for a second }

see the 12 pin when down, the last byte is not Send End.

so Change the HardwareSerial.cpp to:

void HardwareSerial::flush() { if(!_uart || !uart_tx_enabled(_uart)) { return; }

uart_wait_tx_empty(_uart);
long tt =uart_get_baudrate(_uart);
tt=12000000/tt;

delayMicroseconds(tt);

}