Serial console temporarily garbled

Serial console temporarily garbled

[Neil Baylis]

I'm working on an embedded system running a 2.6.32 kernel originally
derived from RHEL6.

The hardware architecture is similar to a PC. The device is a specialized
server. It uses an 8250 compatible serial port for the console.

When it's booting up, everything looks fine until it initializes the serial
driver. At that point the output to the console becomes garbled until (I
think...) getty runs for the console port. Then it's readable again.

It looks as though the initialization of the serial driver is setting the
wrong baud rate, or perhaps some other configuration. During the boot
process, this garbled output happens for about 1 second, during which
probably a few thousand characters of garbage are output.

The grub boot parameter specifies "console=ttys0,57600"
The getty line for the console specifies "T0:23:respawn:/sbin/getty -L
ttys0 57600 vt100"

It's not clear to me how the serial driver is supposed to be initialized to
the right baud rate. Is the parameter from the boot line supposed to be
used?

(Just to complicate matters, we're using a Debian userspace with this
kernel).

Here's how it looks on the console:

[    4.429923] Non-volatile memory driver v1.3

[    4.438325] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled

?[    4.615305] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a ST16650V2

;s?6T=$?????;s?v?=????P%1D?????K ??- %1??;s?5V=????!?E?)???

U000&?P%19)$%??;s61v=? 0?0?1r2C?J ???0424??6/F3d ?0 ??4!



Much garbage deleted...



???!V??D???'??;?s?W?G=d????5?V$????Y? ??&V%j?;?s1&??=t?E%??i?)?D!6f???Loading,
please wait...

PuTTYPuTTYPuTTYBegin: Loading essential drivers ... done.

Begin: Running /scripts/init-premount ...
PuTTYPuTTYPuTTYPuTTYPuTTYPuTTYPuTTYPuTTYdone.

Begin: Mounting root file system ... Begin: Running /scripts/local-top ...
done.

If anyone can point me in the right direction to understand this, that
would be great. I think the repeated 'PuTTY' strings result from control
characters being sent to the terminal, which is PuTTY. It's answerback
string is 'PuTTY' by default.

Thanks,

Neil Baylis
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Serial console temporarily garbled

[Dave Hylands]

Hi Neil,

On Tue, Nov 22, 2011 at 10:20 AM, Neil Baylis <neil.baylis@gmail.com> wrote:
> I'm working on an embedded system running a 2.6.32 kernel originally derived
> from RHEL6.
>
> The hardware architecture is similar to a PC. The device is a specialized
> server. It uses an 8250 compatible serial port for the console.
>
> When it's booting up, everything looks fine until it initializes the serial
> driver. At that point the output to the console becomes garbled until (I
> think...) getty runs for the console port. Then it's readable again.
>
> It looks as though the initialization of the serial driver is setting the
> wrong baud rate, or perhaps some other configuration. During the boot
> process, this garbled output happens for about 1 second, during which
> probably a few thousand characters of garbage are output.
>
> The grub boot parameter specifies "console=ttys0,57600"

Did you mean ttyS0? The capital S is significant.

The serial ports default to 9600 baud, which is probably what the
garbage coming out is.

> The getty line for the console specifies "T0:23:respawn:/sbin/getty -L ttys0
> 57600 vt100"

This should probably also be ttyS0

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com

Serial console temporarily garbled

[Neil Baylis]

My apologies for the confusion, I meant ttyS0. I mistyped when composing
the email.

Neil

On Tue, Nov 22, 2011 at 10:43 AM, Dave Hylands <dhylands@gmail.com> wrote:

> Hi Neil,
>
> On Tue, Nov 22, 2011 at 10:20 AM, Neil Baylis <neil.baylis@gmail.com>
> wrote:
> > I'm working on an embedded system running a 2.6.32 kernel originally
> derived
> > from RHEL6.
> >
> > The hardware architecture is similar to a PC. The device is a specialized
> > server. It uses an 8250 compatible serial port for the console.
> >
> > When it's booting up, everything looks fine until it initializes the
> serial
> > driver. At that point the output to the console becomes garbled until (I
> > think...) getty runs for the console port. Then it's readable again.
> >
> > It looks as though the initialization of the serial driver is setting the
> > wrong baud rate, or perhaps some other configuration. During the boot
> > process, this garbled output happens for about 1 second, during which
> > probably a few thousand characters of garbage are output.
> >
> > The grub boot parameter specifies "console=ttys0,57600"
>
> Did you mean ttyS0? The capital S is significant.
>
> The serial ports default to 9600 baud, which is probably what the
> garbage coming out is.
>
> > The getty line for the console specifies "T0:23:respawn:/sbin/getty -L
> ttys0
> > 57600 vt100"
>
> This should probably also be ttyS0
>
> --
> Dave Hylands
> Shuswap, BC, Canada
> http://www.davehylands.com
>
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