Here is a rundown of were we are:
We have 2 distinct issues:
1. The inability to read the "control lines" status without altering the
status of DTR/RTS
2. The simplification of working with the "control lines" from shell
scripts.
We have 3 ways to resolve this:
1. Add a new parameter to the open() call so you can open the device
file like:
fd = open(comPort,O_NO_ALTER_DTR_RTS)
Pros: Would open access to elaborate programs written in C
Cons: When I read
http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html its
seems that playing with the open() system call may be off limits. There
is an options called "O_TTY_INIT" but its seems unused.
Cons: Would not really simplify working with scripts.
2. Add a single file in sysfs something like:
/sys/class/tty/ttyUSB0/device/TIOCM
Pros: Access to everything with a single read from a shell script.
Cons: The script would needs to parse out the individual bits. You
would also need to read the state of DTR/RTS before you can write a new
value to /sys/class/tty/ttyUSB0/device/TIOCM if you want to change only
one of the two. Actually this is currently the case with TIOCMGET and
TIOCMSET.
3. Add multiple files to sysfs something like this:
/sys/class/tty/ttyUSB0/device/RTS (rw, Request To Send)
/sys/class/tty/ttyUSB0/device/CTS (r, Clear To Send)
/sys/class/tty/ttyUSB0/device/DSR (r, Data Set Ready)
/sys/class/tty/ttyUSB0/device/DCD (r, Data Carrier Detect)
/sys/class/tty/ttyUSB0/device/DTR (rw, Data Terminal Ready)
/sys/class/tty/ttyUSB0/device/RI (r, Ring Indicator)
Pros: Very easy to script. Ability to set DTR directly without any
prior read.
Cons: Could have race conditions when needing to read multiple pins.
At this point we need some heavy hitters like Greg to let us know what
they think.
Gérald
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