The zs module supports the standard set of termio ioctl() calls.
If the CRTSCTS flag in the c_cflag field is set, output will be generated only if CTS is high; if CTS is low, output will be frozen. If the CRTSCTS flag is clear, the state of CTS has no effect.
If the CRTSXOFF flag in the c_cflag field is set, input will be received only if RTS is high; if RTS is low, input will be frozen. If the CRTSXOFF flag is clear, the state of RTS has no effect.
The termios CRTSCTS (respectively CRTSXOFF) flag and termiox CTSXON (respectively RTSXOFF)
can be used interchangeably.
Breaks can be generated by the TCSBRK, TIOCSBRK, and TIOCCBRK ioctl() calls.
The state of the DCD, CTS, RTS, and DTR interface signals may be queried through the use of the TIOCM_CAR, TIOCM_CTS, TIOCM_RTS, and TIOCM_DTR arguments to the TIOCMGET ioctl command, respectively. Due to hardware limitations, only the RTS and DTR signals may be set through their respective arguments to the TIOCMSET, TIOCMBIS, and TIOCMBIC ioctl commands.
The input and output line speeds may be set to any of the speeds supported by termio. The input and output line speeds cannot be set independently; for example, when you set the the output speed, the input speed is automatically set to the same speed.
When the driver is used to service the serial console port, it supports a BREAK condition that allows the system to enter the debugger or the monitor. The BREAK condition is generated by hardware and it is usually enabled by default. A BREAK condition originating from erroneous electrical signals
cannot be distinguished from one deliberately sent by remote DCE. The Alternate Break sequence can be used to remedy this.
Due to a risk of incorrect sequence interpretation, binary protocols such as PPP, SLIP, and others should not be run over the serial console port when Alternate Break sequence is in effect. By default, the Alternate Break sequence is three characters: carriage return, tilde and control-B (CR ~ CTRL-B),
but may be changed by the driver. For more information on breaking (entering the debugger or monitor, see kbd(1) and kb(7M).