Serial console ports on systems with no console connected.

[Richard Williams]

I've had a board hang in the same place before. Can't remember exactly the
circumstances but it was triggered by me turning on a lot of debug messages
in kernel modules.

Perhaps buffer overrun on the console port?

Regards,
Richard

-----Original Message-----
From: Arun Dharankar [mailto:ADharankar at ATTBI.Com]
Sent: Wednesday, 10 July 2002 12:08 a.m.
To: Wolfgang Denk
Cc: linuxppc-embedded at lists.linuxppc.org
Subject: Re: Serial console ports on systems with no console connected.



Hello, and thanks for your reply!

The board has SCC4 and SMC1 based serial ports. I have
tried both of these as console ports under Linux and PPCBOOT.
PPCBOOT code is unmodified (as it is from the distribution) for
SCC4 and SMC1 code. The Linux code is unmodified for
SMC1, and I see this behavior in case of both these serial
ports.

The place where the BDI shows the PC to hang is in
serial_putc(...) waiting for the transmit buffer to be drained by the
8260:

    /* Wait for last character to go.
    */
    while (tbdf->cbd_sc & BD_SC_READY)
        ;

Ofcourse, when the cable is present, things work well.

Though I dont see any code path, or from hardware perspective
what could be wrong, I am open to any guesses/hints at
debugging it.


Best regards,
-Arun.



On Tuesday 09 July 2002 01:14 am, Wolfgang Denk wrote:
> In message <200207082127.16518.ADharankar at ATTBI.Com> you wrote:
> > This question is common to both ppcboot and ppc-linux.
> > The ppcboot I am using is 1.1.5 and Linux kernel 2.4.18.
> >
> > If there is no console connected to the serial console port,
> > is it true that a thread sending output to it hangs? If this is
>
> No, this is NOT true.
>
> Why should it? There is no flow control used - neither in the PPCBoot
> nor in the Linux UART drivers...
>
> > I have a MPC8260ADS based board, and see the above
>
> ...at least not in the standard MPC8xx and MPC8260 UART drivers.
>
> > behavior under ppcboot. Under Linux using a BDI debugger
> > the thread sending output to the console hangs. Perhaps
>
> You must be doing something wrong.
>
> Wolfgang Denk


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