Re: GDB and Dragonball EZ.

[Stan Shebs <shebs at cygnus dot com>]

   From: David Williams <davidwilliams@ozemail.com.au>
   Date: Mon, 22 Nov 1999 22:30:45 +1100

   I need some help to get started in modifying the appropriate parts of GDB 
   so that I can remotely debug my system.
   I am using the Motorola MC68EZ328 (Dragonball EZ). It has a hardware 
   breakpoint capability built in (not BDM as Dragonball is a 68000 core not 
   CPU32). The hardware breakpoint capability would seem to be peculiar to 
   this processor so I believe I will have to modify some parts(drivers etc) 
   of GDB to use it. The processors breakpoint facility allows you to define a 
   single address (and mask for ranges) to set a break-point on for either 
   instruction or data accesses - read or write. This is great as can then set 
   break-points in code without having to have code in RAM! A small problem is 
   it only allows one hardware breakpoint to be set at a time.

Interesting!  There is some hardware breakpoint support in GDB
already, though it's mostly used for native systems.  Look for the
macro TARGET_HAS_HARDWARE_WATCHPOINTS to find some relevant sources.

   Another "small" problem is that I don't have a spare RS-232 port to 
   communicate to GDB with. I have only one on my system. I have two options, 
   as I see it. Firstly I could share the serial port between GDB and my 
   application. One problem with this approach is will make debugging the IrDA 
   part of my application more difficult. Secondly I could try and implement a 
   software UART using the handshaking lines. Currently I think this second 
   option may be better as long as a simple half duplex software UART can be 
   implemented and provide adequate communications.

The second option sounds harder to me, but mostly because it sounds like
some ugly driver hacking.  The latest GDB sources include a mechanism
to allow an application and GDB to share a single line when using the
remote protocol.  Look for the function minitelnet() in remote.c.

   Anyway what I would like to know is which parts of GDB to look at and what 
   existing drivers/stubs etc I should use as templates for modification? Are 
   DLDT drivers appropriate? Is GDB stub ("remote target") appropriate?

I would say so.  An example m68k stub is in gdb/m68k-stub.c.  It's not
the prettiest code in the world, but note that there's not even a GPL
on it; the expectation is that you take and modify for your own purposes.

   Please point me in the right direction I am currently lost in a sea of 
   documentation and source code with no maps!

   Note: I am currenty using ECGS 1.1.2 and have downloaded GDB 4.18 
   distribution.

GDB has evolved quite a bit since 4.18, and includes hardware
breakpoint ("Z packet") and the minitelnet features that you probably
want to use.  You can get a copy of the latest sources from
sourceware.cygnus.com/gdb.  Also check out the user's manuals and the
internals manuals (in gdb/doc), we've been adding to them recently.

								Stan