Repository navigation
SoftwareSerial.flush() returns too early #2904
Description
Bug Description
SoftwareSerial.flush() returns before the last byte is sent, i.e. after sending 2nd last byte. This is unexpected and different from HardwareSerial.flush() and other core implementations
Reproduction
- flash this sketch SoftwareSerial_flush.zip
- measure pins D11(=TxD) and D3(=testpin) with logic analyzer
Expected behavior
SoftwareSerial.flush() should return after the last byte from SoftwareSerial.write(buf, len) has been sent. This is the behavior of HardwareSerial.flush() and also other core implementations
Screenshots
Expected behavior (from HardwareSerial.flush()):
Actual behavior of SoftwareSerial.flush()):
Desktop:
- OS: Linux / Ubuntu
- STM32 core v2.12.0
- Arduino IDE version: 2.3.7
- STM32 core version: 2.12.0
Board:
- Name: Nucleo-STM32L432KC
Activity
bugfix SoftwareSerial.flush(), see stm32duino#2904
gicking commentedon Jan 26, 2026
PS: I just added a pull request which addresses this issue
[-]SoftwareSerial.flush() returns too early[/-][+]SoftwareSerial.flush() returns too early (PR provided)[/+][-]SoftwareSerial.flush() returns too early (PR provided)[/-][+]SoftwareSerial.flush() returns too early[/+]fix: SoftwareSerial flush() issue
fix: SoftwareSerial flush() issue