From mboxrd@z Thu Jan  1 00:00:00 1970
From: greg@kroah.com (Greg KH)
Date: Wed, 26 Apr 2017 14:49:19 +0200
Subject: kgdb debug with ttyUSB0 instead of ttyS0
In-Reply-To: <20170426112355.GA16804@graute-opti>
References: <20170425211138.GA3230@ripley> <20170426043701.GB5734@kroah.com>
	<20170426112355.GA16804@graute-opti>
Message-ID: <20170426124919.GA12061@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

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