Many modern RS-485 serial devices such as the ones from FTDI already
operate in RS-485 mode by default and will work with tio out of the box.
However, there are some RS-232/485 devices which need to be switched
from e.g. RS-232 to RS-485 mode to operate accordingly on the physical
level.
This commit implements the switching mechanism and interface required to
enable RS-485 mode. It only works on Linux and with serial devices which
use device drivers that support the Linux RS-485 control interface.
The RS-485 feature is detailed via the following options:
--rs-485 Enable RS-485 mode
--rs-485-config <config> Set RS-485 configuration
Set the RS-485 configuration using the following key or key value pair
format in the configuration field:
RTS_ON_SEND=value Set logical level (0 or 1) for RTS pin when sending
RTS_AFTER_SEND=value Set logical level (0 or 1) for RTS pin after sending
RTS_DELAY_BEFORE_SEND=value Set RTS delay (ms) before sending
RTS_DELAY_AFTER_SEND=value Set RTS delay (ms) after sending
RX_DURING_TX Receive data even while sending data
If defining more than one key or key value pair, they must be comma
separated.
Example use:
$ tio /dev/ttyUSB0 --rs-485 --rs-r485-config=RTS_DELAY_AFTER_SEND=50,RX_DURING_TX
Optional arguments, as parsed by the getopt_long mechanism, are
inherently inconsistent with how you define required arguments.
To avoid confusion we decide to avoid this inconsistency by replacing
optional options with additional options with required argmuments.
