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RE: dz console serial

To: linux-mips@fnet.fr
Subject: RE: dz console serial
From: Harald Koerfgen <harald.koerfgen@netcologne.de>
Date: Wed, 09 Sep 1998 18:36:29 +0200 (MEST)
In-reply-to: <Pine.LNX.3.96.980908233834.21792G-100000@apt4g.a3nyc.com>
Organization: none
Reply-to: "Harald Koerfgen" <harald.koerfgen@netcologne.de>
Sender: harry@franz.no.dom
Hi Thomas,

On 09-Sep-98 Thomas Riemer wrote:
> Thanks for the helpful hints - I've actually managed to get characters
> flowing through the serial line at this point.
> 
> I noticed in my debugging that the kernel was generating an error
> that it couldn't open /dev/console  - it looked like it was failing
> on dz_open.  Anyone tell me the vague story on how /dev/console
> gets mapped to the serial port?  Or at least point me at the right
> file.

linux/Documentation/serial_console.txt :-).

--- begin quote ---

If no console device is specified [in the command line options], the first
device found capable of acting as a system console will be used. At this time,
the system first looks for a VGA card and then for a serial port. So if you
don't have a VGA card in your system the first serial port will automatically
become the console.

--- end quote ---

The first serial port is usually /dev/ttyS0.

>From dz_init():

..
  i = 0;
  for (info = &multi[i]; i < DZ_NB_PORT;  i++) {
    info->magic = SERIAL_MAGIC;
    info->port = (unsigned) dec_serial_base;
    info->line = i;
    info->tty = 0;
    ...
  }
..

>From dz_open():

static int dz_open (struct tty_struct *tty, struct file *filp)
{
  struct dz_serial *info;
  int retval, line;

  line = MINOR(tty->device) - tty->driver.minor_start;
  /* The dz lines for the mouse/keyboard must be
   * opened using their respective drivers.
   */
  if ((line < 0) || (line >= DZ_NB_PORT))
    return -ENODEV;

  if ((line == DZ_KEYBOARD) || (line == DZ_MOUSE))
    return -ENODEV;

  ... 
}

>From dz.h:

#define DZ_KEYBOARD      0x0000               /* line 0 = keyboard */

That means:

  open("/dev/console") -> dz_open(line 0) -> line == DZ_KEYBOARD
    -> return -ENODEV;

You can try passing a commandline option to the kernel:

<insert_your_boot_command_here> nbImage console=ttyS3

or change the mapping of line numbers to actual lines.

Hope this helps.
---
Regards,
Harald

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