kgdb debug with ttyUSB0 instead of ttyS0

[Joe Smith]

The options you suggested are not clear to me. Can you elaborate how I
would debug live kernel when all I have on the two systems is usb. Can you
list the cable that I can use/order.

Thanks.

On Wed, Apr 26, 2017 at 5:49 AM, Greg KH <greg at kroah.com> wrote:

> On Wed, Apr 26, 2017 at 01:23:55PM +0200, Oliver Graute wrote:
> > On 26/04/17, Greg KH wrote:
> > > On Tue, Apr 25, 2017 at 11:11:38PM +0200, Oliver Graute wrote:
> > > > Hello list,
> > > >
> > > > i'am using a null modem cable with two usb to serial converts on both
> > > > ends between my develop and my target machine. The connection is
> fine.
> > > > On both machines the serial interface is /dev/ttyUSB0 for this
> connection.
> > > >
> > > > On the target machine I try to enable kgdboc
> > > >
> > > > echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
> > > >
> > > > but only got:
> > > >
> > > > echo write error: No such device
> > > >
> > > > if I try:
> > > >
> > > > echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
> > > >
> > > > is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?
> > >
> > > USB needs interrupts in order to run properly, which kgdb doesn't
> enable
> > > when you stop the target, for obvious reasons :)
> >
> > ok that make sense
> >
> > > Stick to a "real" serial connection and you should be fine.
> >
> > thats not so easy. Even the old notebooks today lacks a "real" serial
> > connection. Perhaps I should use a raspberry as target. There I can get
> > a serial over the gpios.
>
> Why do you need to use a notebook where Linux works already for kgdb?
> That's traditionally only used to bring up new hardware platforms.
>
> Also, there is USB serial debugging cables as there is a special mode in
> the USB 2 and 3 controllers that can be enabled to handle serial
> messages without interrupts for console/printk early messages that
> people use.  The cables are not cheap to enable this, but worth it if
> you have to debug this type of target system.
>
> Good luck!
>
> greg k-h
>
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-- 
JS
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