RE: modifying line state manually on ttyS

RE: modifying line state manually on ttyS

[Ed Vance]

On Mon, Apr 07, 2003 at 8:42 AM, Michael Buesch wrote:
> On Monday 07 April 2003 16:16, Alan Cox wrote:
> > TxD is a bad choice. A lot of the hardware cannot control TXD this
> > way. DTR is the usual one because it is easy to handle but there
> > are other control lines you can drive directly (see TIOCGMODEM)
> 
> Oh great, you have just discovered the reason, why my driver 
> is working
> on my Pentium1-PC but not on my Pentium4-PC. It's simply not supported
> by hardware.  I've spent hours and hours about this. :)
> 
> My device is actually using DTR and RTS. What line could I 
> use instead of
> TxD? Is it possible to use CTS for this, although it is normally a
> "input-signal", but not a "output-signal" like RTS?
> 
No, CTS cannot operate as an output. 

The following ioctl calls are implemented in the generic serial driver,
/usr/src/linux*/drivers/char/serial.c:

  Modem Lines
     On special files representing serial ports, the  modem  con-
     trol  lines  supported  by the hardware can be read, and the
     modem status lines supported by the hardware can be changed.
     The  following  modem  control  and status lines may be sup-
     ported by a device; they are defined by <asm/termios.h>:

          TIOCM_DTR      data terminal ready  (DTE output)
          TIOCM_RTS      request to send      (DTE output)
          TIOCM_CTS      clear to send        (DTE input)
          TIOCM_CAR      carrier detect       (DTE input)
          TIOCM_RNG      ring                 (DTE input)
          TIOCM_DSR      data set ready       (DTE input)
          TIOCM_OUT1     UART OUT1 signal     (misc output)
          TIOCM_OUT2     UART OUT2 signal     (misc output)

     TIOCM_CD is a synonym  for  TIOCM_CAR,  and  TIOCM_RI  is  a
     synonym for TIOCM_RNG. Not all of these are necessarily sup-
     ported by any particular device; check the manual  page  for
     the device in question. Output signals OUT1 and OUT2 are not
     always  connected to  port interface  pins.  Often  they are
     dedicated to control of  UART special functions or loopback.

     TIOCMBIS       The argument is a pointer  to  an  int  whose
                    value  is  a  mask  containing  modem control
                    lines to be turned  on.   The  control  lines
                    whose bits are set in the argument are turned
                    on; no other control lines are affected.

     TIOCMBIC       The argument is a pointer  to  an  int  whose
                    value  is  a  mask  containing  modem control
                    lines to be turned off.   The  control  lines
                    whose bits are set in the argument are turned
                    off; no other control lines are affected.

     TIOCMGET       The argument is a pointer  to  an  int.   The
                    current  state  of  the modem status lines is
                    fetched and stored in the int pointed  to  by
                    the argument.

     TIOCMSET       The argument is a pointer to an int  contain-
                    ing  a  new  set of modem control lines.  The
                    modem control lines are  turned  on  or  off,
                    depending on whether the bit for that mode is
                    set or clear.

Cheers,
Ed

---------------------------------------------------------------- 
Ed Vance              edv (at) macrolink (dot) com
Macrolink, Inc.       1500 N. Kellogg Dr  Anaheim, CA  92807
----------------------------------------------------------------

Re: modifying line state manually on ttyS

[Michael Buesch]

On Monday 07 April 2003 18:22, Ed Vance wrote:
> No, CTS cannot operate as an output.
>
> The following ioctl calls are implemented in the generic serial driver,
> /usr/src/linux*/drivers/char/serial.c:
> [...]

puh, that's very bad. I have to modify the device.
(Better had informed before building it. :)

Thanks to all, who helped me (although this was not the
very correct list :)

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity

modifying line state manually on ttyS

[Michael Buesch]

Hi.

I have asked in many other mailing-lists, but I got no good
solution for my problem, so I try to ask here, although it may
not be the exaclty correct list for it.

I have developed my own device, that is connected to ttyS0.
To talk to my device, I need to set the state of the TxD line
manually to either 0 or 1 (+12v or -12v). What I try to say is,
I don't want to write a whole byte to the port, but only one single
bit, that then stays persistent on the line, until I reset its state.
Better sayed, I want to handle TxD line, like it's possible for
DTR-line for example.

Is kernel-support by the ttyS driver present for this, or do I
have to write my own driver for my device. I'm trying to
implement the driver in user-space, but I didn't find a solution
to set linestate of TxD.

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity

Re: modifying line state manually on ttyS

[Alan Cox]

On Llu, 2003-04-07 at 16:02, Michael Buesch wrote:
> I have developed my own device, that is connected to ttyS0.
> To talk to my device, I need to set the state of the TxD line
> manually to either 0 or 1 (+12v or -12v). What I try to say is,

TxD is a bad choice. A lot of the hardware cannot control TXD this
way. DTR is the usual one because it is easy to handle but there
are other control lines you can drive directly (see TIOCGMODEM)

Re: modifying line state manually on ttyS

[Michael Buesch]

On Monday 07 April 2003 16:16, Alan Cox wrote:
> TxD is a bad choice. A lot of the hardware cannot control TXD this
> way. DTR is the usual one because it is easy to handle but there
> are other control lines you can drive directly (see TIOCGMODEM)

Oh great, you have just discovered the reason, why my driver is working
on my Pentium1-PC but not on my Pentium4-PC. It's simply not supported
by hardware.  I've spent hours and hours about this. :)

My device is actually using DTR and RTS. What line could I use instead of
TxD? Is it possible to use CTS for this, although it is normally a
"input-signal", but not a "output-signal" like RTS?

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity

Re: modifying line state manually on ttyS

[Sergei Organov]

Michael Buesch <freesoftwaredeveloper@web.de> writes:
> Hi.
> 
> I have asked in many other mailing-lists, but I got no good
> solution for my problem, so I try to ask here, although it may
> not be the exaclty correct list for it.
> 
> I have developed my own device, that is connected to ttyS0.
> To talk to my device, I need to set the state of the TxD line
> manually to either 0 or 1 (+12v or -12v). What I try to say is,
> I don't want to write a whole byte to the port, but only one single
> bit, that then stays persistent on the line, until I reset its state.
> Better sayed, I want to handle TxD line, like it's possible for
> DTR-line for example.

Do ioctl(fd, TIOCSBRK, 0) / ioctl(fd, TIOCCBRK, 0) help?

-- 
Sergei.

Re: modifying line state manually on ttyS

[Michael Buesch]

On Monday 07 April 2003 17:34, Sergei Organov wrote:
> Do ioctl(fd, TIOCSBRK, 0) / ioctl(fd, TIOCSBRK, 0) help?

What does it do? I haven't found a description for TIOCSBRK, TIOCSBRK.

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity

Re: modifying line state manually on ttyS

[Sergei Organov]

Michael Buesch <freesoftwaredeveloper@web.de> writes:
> On Monday 07 April 2003 17:34, Sergei Organov wrote:
> > Do ioctl(fd, TIOCSBRK, 0) / ioctl(fd, TIOCSBRK, 0) help?
> 
> What does it do? I haven't found a description for TIOCSBRK, TIOCSBRK.

Changes the state of TxD line, I believe. Did you hear about "break
condition"? It sets/clears the "break condition", at least for me ;)

-- 
Sergei.

Re: modifying line state manually on ttyS

[Michael Buesch]

On Monday 07 April 2003 19:01, Sergei Organov wrote:
> Michael Buesch <freesoftwaredeveloper@web.de> writes:
> > What does it do? I haven't found a description for TIOCSBRK, TIOCSBRK.
>
> Changes the state of TxD line, I believe. Did you hear about "break
> condition"? It sets/clears the "break condition", at least for me ;)

Oh my goodness, it works. Thank you *very* much!

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity

Re: modifying line state manually on ttyS

[Richard B. Johnson]

On Mon, 7 Apr 2003, Michael Buesch wrote:

> Hi.
>
> I have asked in many other mailing-lists, but I got no good
> solution for my problem, so I try to ask here, although it may
> not be the exaclty correct list for it.
>
> I have developed my own device, that is connected to ttyS0.
> To talk to my device, I need to set the state of the TxD line
> manually to either 0 or 1 (+12v or -12v). What I try to say is,
> I don't want to write a whole byte to the port, but only one single
> bit, that then stays persistent on the line, until I reset its state.
> Better sayed, I want to handle TxD line, like it's possible for
> DTR-line for example.
>
> Is kernel-support by the ttyS driver present for this, or do I
> have to write my own driver for my device. I'm trying to
> implement the driver in user-space, but I didn't find a solution
> to set linestate of TxD.
>
> Regards
> Michael Buesch.

Well ttyS0 is connected to the rest of the machine using a UART.
This means that you can't control TxD directly. I suggest that
you use the parallel printer-port. This port allows you to set
individual bits and they remain <forever> in the last state set.
An ordinary (old-fashioned) printer-port allows you to set or
reset 8 data bits plus three control bits. The newer ones allow
you to read and write up to 16 bits.

Now, if you really need the +/- 12 volts that you think you
will get out of a UART, please measure it first. Many new computers
use I/O chips that only provide +/- 5 volts! Anyway, you can use the
modem-control bits if you need that kind of voltage swing. You can
set/reset modem control bits using the TIOCMGET/TIOCMSET ioctl()
calls. You probably want to disable the SIGHUP signal before
you muck with those bits. Some versions of Linux will send the
hangup signal to the TTY owner even though it's not the controlling
terminal for the process. This could cause your program to exit
for "unknown" reasons; signal(SIGHUP, SIG_IGN) prevents such problems.


Cheers,
Dick Johnson
Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.

Re: modifying line state manually on ttyS

[Michael Buesch]

On Monday 07 April 2003 17:51, Richard B. Johnson wrote:
> This means that you can't control TxD directly. I suggest that
> you use the parallel printer-port. This port allows you to set

That's my problem. parallel-port is used by a printer and I don't
wanna by an expensive extension card for second parport. :)

> Now, if you really need the +/- 12 volts that you think you
> will get out of a UART, please measure it first. Many new computers
> use I/O chips that only provide +/- 5 volts! Anyway, you can use the

That's no problem, because I "down-volt" it to 4.7V before using it.

> calls. You probably want to disable the SIGHUP signal before
> you muck with those bits. Some versions of Linux will send the
> hangup signal to the TTY owner even though it's not the controlling
> terminal for the process. This could cause your program to exit
> for "unknown" reasons; signal(SIGHUP, SIG_IGN) prevents such problems.

Thanks for this important information.

Regards
Michael Buesch.

-- 
My homepage: http://www.8ung.at/tuxsoft
fighting for peace is like fu**ing for virginity