mpc8xx-2.2.13 kernel hangs during boot.

Alan Mimms alan at
Tue Feb 1 12:49:16 EST 2000

On Tue, 01 Feb 2000, Brendan John Simon wrote:
> Alan Mimms wrote:
> > Brendan,
> >
> > We use a serial connection to debug our applications with GDB all the time
> > using stubs that are part of our "OS".  It certainly is possible.  We put the
> > devices on the end of a 24 port Livingston Portmaster terminal server and then
> > setup the ports as raw data ports to which we connect with GDB running on our
> > main build/debug box.  That way the user can debug something in another room or
> > across the planet very easily through the network.
> Cool.  A little overkill never hurt anybody :)
> I'll assume one build/debug box connected directly to the target via a serial cable
> or ethernet for now.

I see what you mean, but I still think it's a necessity.  It's not overkill if
it means I don't have to wander across the hall every 5 minutes to dink with the
platform or sit in a room full of LOUD fans to work and debug.

> > I debugged my initial port of the linux kernel to our platform using just this
> > kind of interface.  You have to commandeer the serial hardware away from the
> > driver - I simply didn't tell the kernel there was a device there and
> > configured it "manually" from the GDB nub initialization function which I
> > called early in main.c.  This works fine for KERNEL debugging.
> When you say configured manually what exactly do you mean.
> Is this in the kernel itself ?
> When you say main.c do you mean init/main.c in the linux kernel source tree ?
> Has this got anything to do with the kgdb option in the "make config" process ?
> Can ethernet be used to debug the kernel or is a serial port the only or best way to
> go ?

I DO mean init/main.c.  I mean "manually" in the sense that the low level
driver I used in my gdb nub has an "init" call made from init/main.c to
setup the UART registers properly (baud rate, etc.).  The nub UART driver simply
polls the UART and does simple one byte read/write operations to it.  The nub
has the necessary (simple) hex/unhex conversion routines for the GDB serial
protocol.  Doesn't use anything else so you can theoretically debug the
kernel's version of printf with breakpoints and everything without screwing up
the debugger by debugging code it depends upon.

> > For application debugging, you probably want to live in user space.  You COULD
> > use gdbserver, I think, although I have no experience or knowledge of this.
> I'm pretty sure gdbserver is the way to go for debugging applications.  A TCP
> connection is a nice way to debug this.
> Thanks,
> Brendan Simon.
Alan Mimms     Packet Engines, Inc.     Spokane, Washington [99214-0497]
  USA, Earth, Sol, Milky Way, The Local Group, Virgo Supercluster, U0
Despite the cost of living, have you noticed how popular it remains?
  -- Steven Wright?

** Sent via the linuxppc-embedded mail list. See

More information about the Linuxppc-embedded mailing list