Initialize a serial device. unit is a number in the range 0-3
specifying which serial port to use; default is 0, which corresponds to
the port often called COM1. port is the I/O port where the UART
is to be found; if specified it takes precedence over unit.
speed is the transmission speed; default is 9600. word and
stop are the number of data bits and stop bits. Data bits must
be in the range 5-8 and stop bits must be 1 or 2. Default is 8 data
bits and one stop bit. parity is one of `no', `odd',
`even' and defaults to `no'. The option --device
can only be used in the grub shell and is used to specify the
tty device to be used in the host operating system (see Invoking the grub shell).
The serial port is not used as a communication channel unless the
terminal command is used (see terminal).
This command is only available if GRUB is compiled with serial
support. See also Serial terminal.