Re: proposed extension for jtag debugging

[Chris Johns <chris@contemporary.net.au>]

Edward L. Hepler wrote:
> 
> I'd very much like to hear about this as it sounds similar to what I
> have done.   I added a target to the "mips" code to directly control
> a JTAG cable connected to a PC parallel port.   It did not use
> gdbserver.   As an aside, I also use GDB to control a "C" based
> emulator and a VHDL based simulator.
> 
> Since then, I have been looking into using gdbserver so I won't have
> to apply patches to GDB...  I'm also hoping that since gdbserver is
> a separate process, some of the control issues that arise when trying
> to control a separate VHDL simulator may be more easy handled...
> 

The move to the remote protocol and a gdbserver has all been positive and 
worth the effort. For us the key feature added to gdb that enabled a smooth 
transition has been the ability to define registers overs the remote protocol. 
As new processors are added we can add support without the need to rebuild gdb.

Our gdbserver code is in CVS in a directory m68k/gdbserver. The project link 
was posted earlier but here it is again:

  http://bdm.sourceforge.net/

The gdbserver code was taken from a recent gdb and has a number of changes to 
suite an embedded target rather than a host OS like Linux. They are:

  1. Builds for Unix and Windows (MinGW).
  2. Supports the GDB remote pipe mode.
  3. Ability to control the XML register definition based on the
     detected processor.
  4. Register cache changes to support hardware mapped register. The
     register cache only updated the hardware when a go, step etc
     was issues and this causes problems when initialising hardware.
     The cache has been extended to allow a back end to define which
     registers need to be passed directly to hardware.

I am sure there are other things I have forgotten.

I plan to get paper work in place and to send patches but time has been limited.

Regards
Chris