CODEWITHSUNDEEP
linuxserial-portttytermios
user1284631
user1284631

Reputation: 4606

Command-line configurating a TTY device

My task at the moment is to port a driver for some 16550-compatible chip from QNX to Linux. The chip provides several UARTs, each one seen as a standard 16550 serial port, albeit with some extensions.

Now, in QNX, the whole device driver is packed into a standalone executable, that acts both as a driver and as an initial configurator for the provided UARTs (baud rates, loopback modes etc.) That is just natural in QNX because there device drivers run in user space and are little more than standard executables.

On Linux, OTOH, the driver is now implemented as a kernel module, loadable at will. More, that module is provided by the producer, so I would not want to modify or patch it too much.

For me, the remaining task is to provide some mechanism for setting up those UARTs' parameters. They are seen as /dev/ttyPREFIXX devices. I intend to do that through a standard C-programmed executable calling standard termios (ie tcsetattr() or ioctls) on the serial ports of interest.

Which leads me to the question: is my approach right? And, if yes, then how to achieve a persistent configuration? As I perceive the fact (from this example: http://www.easysw.com/~mike/serial/serial.html), the termios functions act on OPEN devices. In short: they open a device, they set up the parameters, they read or write, then close the port. After closing the port, is the configuration (baud rate etc.) lost? I hope it is not, because it is stored, already, into the hardware.

Can somebodey confirm to me that the configuration is persistent? And, if not, how to achieve that persistence, for the future applications that would open again that port and will expect it with some pre-established parameters? If not, should I modify the module kernel to accept some parameters and, then, do the configuration at the load time?

The approach that I intend for now is to write that C executable that opens the ports, sets up their configuration, then close the ports. I hope the latter applications will see the ports with the desired configuration.

Thank you.

Upvotes: 2

Views: 6774

Answers (2)

themel
themel

Reputation: 8895

You might want to have a look at stty and setserial. The venerable Serial-HOWTO (wow, when was the last time I actually recommended a HOWTO to anyone?) is probably also a good starting point.

Upvotes: 1

user1284631
user1284631

Reputation: 4606

Well, I found the answer here: http://www.gnu.org/software/libc/manual/html_node/Mode-Functions.html#Mode-Functions

Quote: "Although tcgetattr and tcsetattr specify the terminal device with a file descriptor, the attributes are those of the terminal device itself and not of the file descriptor. This means that the effects of changing terminal attributes are persistent; if another process opens the terminal file later on, it will see the changed attributes even though it doesn't have anything to do with the open file descriptor you originally specified in changing the attributes."

This clears the issue.

Upvotes: 0

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